Jabbur, N. S. (2003). "Endothelial cell studies in patients after photorefractive keratectomy for hyperopia." J Refract Surg 19(2): 142-8.
PURPOSE: To report central and peripheral corneal endothelial cell studies performed as part of the VISX hyperopic photorefractive keratectomy (PRK) clinical trial. METHODS: During this prospective, multicenter clinical trial, which was part of an FDA investigation, endothelial cell specular microscopy was done at five centers. Non-contact central and peripheral cell density, percent hexagonality, and coefficient of variability of cell size were obtained using the Konan Noncon Robo SP-8000FA with BAMBI analysis software. Data were gathered at baseline and at 1, 6, and 12 months after hyperopic PRK. RESULTS: Analysis of results of 171 eyes demonstrated no statistically significant detrimental changes in the corneal endothelium at any postoperative time point. The statistically significant changes noted were interpreted as an improvement in cell morphology and were attributed to the cessation of contact lens wear following treatment. CONCLUSION: Hyperopic PRK with the VISX STAR S2 Excimer Laser System produced no statistically significant adverse effect on the corneal endothelium.
Resch, M. and M. Popper (2003). "[Results of scanning and flying spot technologies in photorefractive keratectomy (PRK) for hypermetropia]." Orv Hetil 144(4): 179-85.
AIM OF THE STUDY: To compare the results of scanning and flying spot laser beam technologies of photorefractive keratectomy (PRK) in eyes with hypermetropic refractive error. PATIENTS AND METHODS: In Group I (n = 800) eyes were treated with scanning technology (Aesculap-Meditec MEL 60), in Subgroup I/1 (n = 482) those eyes, which had a preoperative refractive error between +1.0 and +3.5 D; in Subgroup I/2 (n = 318) the eyes between +3.75 and +6.5 D. In Group II (n = 200) eyes treated with flying spot technology (Aesculap-Meditec MEL 70 G-Scan) were evaluated; in Subgroup II/1 (n = 106) eyes between +1.0 and +3.5 D; in subgroup II/2 (n = 94) eyes between +3.75 and +7.5 D. Follow-up time was 12 months. RESULTS: The preoperative correction need decreased in Group I/1 from +2.88 +/- 1.34 D to +1.26 +/- 1.24 D; in Group I/2 from 64 +/- 2.96 D to +2.46 +/- 1.84 D; in Group II/1 from +2.94 +/- 1.42 D to +0.42 +/- 0.14 D and in Group II/2 from 48 +/- 2.62 D to +0.86 +/- 0.6 D 12 months after PRK. Postoperative uncorrected visual acuity (UCVA) was 1.0 or better in 75.7% within the eyes of Group I/1; it was 22.3% in Group I/2; 80% in Group II/1 and 64.8% in Group II/2. The percentage of the eyes within +/- 1.0 D of targeted refraction was: In Group I/1 86.1%, in Group I/2 45.3%, in Group II/1 92.4% and in Group II/2 78.7%. The best spectacle-corrected visual acuity (BSCVA) decreased by 2 or more Snellen lines among the eyes of Group I/1 in 12%; in Group I/2 in 21%; in Group II/1 in 2.8% and in Group II/2 in 9.6%. In Group I/1 2%, in Group II/1 3.8% of the treated eyes gained 2 or more lines of BSCVA. Among the eyes treated with the scanning model (Group I/2) a central bump-like opacity was observed in 4 eyes (1.2%); among the eyes treated with the flying spot model no similar complication occurred. The postoperative increase of intraocular pressure was observed in 7.5% in Group I/1; in 6.8% in Group I/2; in 7.0% in Group II/1; and in 6.4% in Group II/2. CONCLUSIONS: Flying spot technology was superior to scanning method in each treatment group, difference was greatest in eyes treated with a preoperative refractive error higher than +3.75 D. The upper limit of hypermetropic treatments has increased to +6.0 D in case of flying spot treatments from the previous +3.5 D upper limit of scanning technology.
Liu, S., X. Wu, et al. (2000). "[Analysis of refractive state after excimer laser photorefractive keratectomy in myopia]." Yan Ke Xue Bao 16(2): 143-5, 148.
OBJECTIVE: To evaluate refractive state after excimer laser photorefractive keratectomy (PRK) in patients with myopia. METHODS: 234 cases(391 eyes) followed up for two years were divided into two groups, group I: mild and moderate myopia(< or = -6.00 D), 228 eyes; group II: High myopia(> -6.00 D), 163 eyes. The refractive state of patients at three, six, twelve and twenty-four months postoperatively were monitored. RESULTS: At two years after photorefractive keratectomy (PRK), refractive regression (> -0.5 D), overcorrection(> 1.00 D), undercorrection(> 1.00 D), postoperative residual astigmatism postoperative astigmatism and hyperopia shift in group I were 1.7%, 4.4%, 5.7%, 12.8%, 7.4% and 7.5% respectively, while in high myopia group were 15.9%, 4.9%, 23.3%, 29.7%, 31.1% and 6.7% respectively. CONCLUSION: The results prove that photorefractive keratectomy is an effective, precise, stable and safe method for correction of mild and moderate myopia, but insufficient for high myopia.
Murphy, P. J., D. P. O'Brart, et al. (2003). "Effect of hyperopic photorefractive keratectomy on corneal sensitivity: a longitudinal study." J Refract Surg 19(1): 34-9.
PURPOSE: To investigate corneal sensitivity after photorefractive keratectomy (PRK) for low hyperopia, as measured with a non-invasive stimulus. METHODS: Two experimental groups were recruited: a control group of 17 patients (mean age 61.65 years) who underwent no treatment, and a PRK group of 11 patients (mean age 58.64 years) who underwent one of three attempted hyperopic corrections: +2.00 D (two patients), +3.00 D (four patients), +4.00 D (five patients). Corneal sensitivity was assessed centrally and peripherally, at temporal, medial, and inferior locations, approximately 1 mm from the limbus, using the Non-Contact Corneal Aesthesiometer (NCCA). Measurements were taken at each location for the control group and at preoperative, and postoperative weeks 1 and 2, 1, 3, and 6 months for the PRK group. RESULTS: Comparison of control and PRK groups (preoperative sensation threshold) (t-test): central P=.715, temporal P=.719, medial P=.943, inferior P= .920. Comparison of longitudinal changes in PRK group (one-way ANOVA): central P=.612, temporal P=.997, medial P=.981, inferior P=.993. CONCLUSIONS: Using the Non-Contact Corneal Aesthesiometer, no significant difference was found between the control and PRK groups for preoperative sensation thresholds, and no significant change in corneal sensitivity was found between any of the test time periods at any of the four corneal test locations for the PRK group.
Seitz, B., A. Langenbucher, et al. (2002). "[Pitfalls of IOL Power Prediction After Photorefractive Keratectomy for High Myopia]." Klin Monatsbl Augenheilkd 219(12): 840-50.
BACKGROUND AND PURPOSE: Published experience with eyes after keratorefractive correction of myopia indicates that insertion of the average keratometric readings into standard IOL power predictive formulas will frequently result in substantial undercorrection and postoperative hyperopic refraction or anisometropia after cataract surgery depending on the amount of myopia corrected previously. The purpose of this paper is to discuss the accentuated differences of various approaches to minimize IOL power miscalculations by describing a case report of a patient with excessive myopia as well as a review of the literature. PATIENT AND METHODS: A 50-year old lady presented for cataract surgery on her left eye after having PRK seven years ago elsewhere (refraction - 25.5 - 3.0/20 degrees, central keratometric power 43.0 diopters [D]). Central power before cataract extraction was measured to be 35.5 D (Zeiss Keratometer) and 36.5 D (TMS-1 topography analysis) and refraction was - 3.0 D (before onset of index myopia). Orbscan slit scanning topography analysis displayed an anterior surface power of 36.8 D and a posterior surface power of - 9.3 D. Total axial length was 31.93 mm (optical biometry using Zeiss IOL-Master). The contralateral eye after PRK suffering from a comparable excessive myopia had required an exchange of the IOL implant because of intolerable anisohyperopia of + 6.0 D after primary cataract extraction elsewhere. RESULTS: Corrected corneal power values for the left eye were calculated as follows: (1) spherical equivalent (SEQ) change at spectacle plane 19.0 D, (2) SEQ change at corneal plane 26.2 D, (3) separate consideration of anterior and posterior curvature 27.5 D, (4) consideration of the IOL power misprediction on the fellow eye 29.5 D, (5) subtraction of 24 % of the SEQ change at the spectacle plane from the actually measured keratometry value 29.7 D, (6) clinical estimate from regression analysis performed earlier 30.5 D, (7) change of anterior surface power 34.5 D. Deciding for a presumably "real" corneal power of 28.0 D the Haigis formula was used to aim for - 2.0 D since the patient preferred to read uncorrected. Thus, a 21.0 D IOL was implanted uneventfully in the capsular bag. The stable refraction postoperatively was - 3.5 - 1.0/20 degrees and visual acuity increased to 20/30. Therefore, the "real" power of that cornea must have been around 30 D. CONCLUSIONS: After corneal refractive surgery, various techniques to determine the current corneal power should be compared and the value around which results tend to cluster should be relied on to avoid hyperopia after cataract surgery with lens implantation. In those cases where keratometry and refraction before PRK/LASIK are available, the gold standard is still to subtract the change of the SEQ at the corneal plane from the preoperative central keratometric power, although in the present case report the subtraction of 24 % of the SEQ change at the spectacle plane from the measured corneal power value seemed to produce the best result. Pure subtraction of the SEQ change at the spectacle plane from the corneal power value before refractive surgery has to be avoided in eyes with excessive myopia. The most reliable corrected power value should be inserted in more than one modern third-generation formula (such as Haigis, Hoffer Q, Holladay 2, SRK/T) and the highest power IOL should be implanted. In all instances, the cataract surgeon has to make sure that the corrected K-reading is not wrongly re-converted within the IOL power calculation formula used.
Jankov, M., M. C. Mrochen, et al. (2002). "Experimental results of preparing laser-shaped stromal implants for laser-assisted intrastromal keratophakia in extremely complicated laser in situ keratomileusis cases." J Refract Surg 18(5): S639-43.
PURPOSE: To evaluate the feasibility of laser-shaped stromal implants from a donor eye for correcting extreme high hyperopia with irregular astigmatism and an exceptionally thin corneal bed. METHODS: Thirty-one fresh enucleated porcine eyes were used. The procedure was initiated with mechanical de-epithelialization followed by a lamellar cut with a microkeratome, resulting in a hinged flap (thickness 150 microm, diameter 9.5 mm). The cornea was photoablated with PRK treatment for +8.00 D sphere (hyperopic lenticule group) and -5.00 D sphere (myopic group) by a scanning spot excimer laser. A customized scanning software algorithm was used to create a circumferential cut with a 6.5-mm internal diameter. The lenticule was removed from the stromal bed and measured by a surface profiling system. A clinical case was performed on a patient with previous LASIK and highly irregular hyperopic astigmatism to verify the clinical utility of the experimental setup. RESULTS: Under the microscope, lenticules seemed round, regular, and transparent. The average surface profile of porcine corneas demonstrated good parabolic shape with individual variations as large as 30 microm, probably due to the corneal size and curvature differences between the porcine eye and the human eye--for which the microkeratome is designed. The patient underwent a topography-guided treatment after laser-assisted intrastromal keratophakia (LAIK) and 1-month follow-up showed an increase of UCVA, BSCVA, and central corneal thickness. CONCLUSIONS: The use of modern scanning-spot excimer lasers and microkeratomes enabled us to produce stromal lenticules of good quality, which might be acceptable to implant into a human eye.
Nagy, Z. Z., I. Palagyi-Deak, et al. (2002). "First results with wavefront-guided photorefractive keratectomy for hyperopia." J Refract Surg 18(5): S620-3.
PURPOSE: To compare the results of traditional laser photoablation and wavefront-supported customized ablation (WASCA) in hyperopic photorefractive keratectomy (H-PRK). METHODS: This was a prospective study, comparing two treatment groups, each comprising 40 eyes of 20 patients. Wavefront aberrations were examined using a Shack-Hartmann aberrometer. Preoperative refraction was similar in the two groups; in the traditional H-PRK group (Group 1) it was +3.10 +/- 0.85 D, and in the WASCA-guided group (Group 2) it was +2.90 +/- 0.80 D. H-PRK was performed with the Asclepion-Meditec MEL 70 flying-spot excimer laser. The follow-up time was 6 months. RESULTS: In Group 1, mean postoperative refraction was +0.14 +/- 0.24 D, and in Group 2, -0.10 +/- 0.25 D; mean uncorrected visual acuity was 0.92 +/- 0.16 in Group 1 and 0.95 +/- 0.18 in Group 2. Mean best spectacle-corrected visual acuity was 0.96 +/- 0.04 in Group 1 and 1.06 +/- 0.13 in Group 2. In Group 1, 67.5% (27 of 40 eyes), and in Group 2, 85% (34 of 40 eyes) were within +/-0.50 D of target refraction. Regarding change of spectacle-corrected visual acuity in Group 1, 5% (2 of 40 eyes), and in Group 2, 20% (8 of 40 eyes) gained one Snellen line compared to the preoperative; in Group 1, 10% (4 of 40 eyes), and in Group 2, 12.5% (5 of 40 eyes) lost two Snellen lines. In Group 2, the root mean square value for the higher order aberration increased from the initial 0.134 to 0.257 microm at 6 months after surgery. CONCLUSIONS: WASCA-guided hyperopic-PRK treatment was found to be safe and predictable. The results were better than those achieved with traditional PRK performed using the same flying-spot type excimer laser.
Nagy, Z. Z., G. Munkacsy, et al. (2002). "Photorefractive keratectomy using the meditec MEL 70 G-scan laser for hyperopia and hyperopic astigmatism." J Refract Surg 18(5): 542-50.
PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) using Gaussian flying spot technology in the treatment of hyperopia and hyperopic astigmatism. METHODS: Two hundred eyes were evaluated with 12-month follow-up. An Asclepion-Meditec MEL 70 G-scan flying spot ArF excimer laser with a Gaussian scanner was used (6.0-mm treatment zone and 9.0-mm transition zone). Eyes were divided into four groups: Group 1 (spherical hyperopia up to +3.50 D and astigmatism less than 1.00 D, n=62); Group 2 (hyperopia up to +3.50 D and astigmatism of 1.00 D or more, n=44); Group 3 (hyperopia greater than +3.50 D and astigmatism less than 1.00 D, n=56); and Group 4 (hyperopia greater than +3.50 D and astigmatism of 1.00 D or more, n=38). RESULTS: In Group 1, 82.2% (51/62 eyes) were within +/-0.50 D of target refraction; 88.7% (55/62 eyes) had 20/20 or better uncorrected visual acuity; 1.6% (1/62 eye) lost two or more lines, 3.2% (2/62 eyes) gained two or more lines of spectacle-corrected visual acuity. In Group 2, 68.1% (30/44 eyes) were within +/-0.50 D; 77.2% (34/44 eyes) had 20/20 or better uncorrected visual acuity; 9.1% (4/44 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 3, 76.8% (43/56 eyes) were within +/-0.50 D; 78.6% (44/56 eyes) had 20/20 or better uncorrected visual acuity; 5.4% (3/56 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 4, 42% (16/38 eyes) were within +/-0.50 D; 60.5% (23/38 eyes) had 20/20 or better uncorrected visual acuity; 15.8% (6/38 eyes) lost two or more Snellen lines. CONCLUSION: PRK with the flying spot Meditec MEL 70 G-scan was most safe and effective for low hyperopia.
Ruckhofer, J. (2002). "[Clinical and histological studies on the intrastromal corneal ring segments (ICRS(R), Intacs(R))]." Klin Monatsbl Augenheilkd 219(8): 557-74.
Intrastromal corneal ring segments (ICRS(R), Intacs(R)) are corneal inlays made of PMMA with an arc length of 150 degrees for the correction of low to moderate myopia. This additive and potentially reversible method has recently been developed to clinical usefulness during the last few years. Besides the historical development und the results of the US FDA studies, we focus on the results of the European experience with this technique. For the first time, long-time follow-up results (5 years from a single surgical center) are presented. Morphological changes after implantation of Intacs(R) were investigated in a series of patients by confocal microscopy. Weeks and months after implantation "lamellar channel deposits" regularly appear around the segments. This material consists of intracellular lipids (cholesterol ester, triglyceride and unesterified cholesterol), as we could show in new histological studies on rabbit eyes. New developments of this technique include short arc length segments (130 degrees ) for the correction of myopia concurrent with astigmatism and radially placed corneal inlays (Intrastromal Corneal Segments, ICS(R)) for the correction of hyperopia. In recent years, Intacs(R) have also been implanted in eyes with keratoconus and keratectasia after LASIK. These early results seem to indicate that in certain cases of early keratoconus, these implants can indeed improve corneal geometry and vision. Even in cases of regression or undercorrection after LASIK (with thin corneas), Intacs(R) seem to give promising results in selected cases. Although Intacs(R) do give comparable results regarding both safety and efficacy when compared with PRK and LASIK, this technology has not yet been widely accepted among refractive surgeons. Whether Intacs(R) will play a greater role in routine refractive surgery in the future or will just remain a special device for the correction of keratectasia, keratoconus or regression after LASIK cannot yet be decided with certainty.
Wang, X., J. Shen, et al. (2002). "Intraocular pressure measurement after hyperopic LASIK." Clao J 28(3): 136-9.
PURPOSE: Previous studies have shown that Goldmann applanation tonometry (GAT) underestimates intraocular pressure (IOP) following photorefractive keratometry (PRK) and myopic laser in situ keratomileusis (LASIK). The purpose of this study was to evaluate the reliability of intraocular pressure (IOP) measurements by Goldmann applanation tonometry and pneumotonometry (PT) after hyperopic LASIK. METHODS: The IOPs of 20 eyes of 15 patients who underwent hyperopia LASIK were prospectively evaluated. Central and peripheral IOP were measured with GAT and PT, and central and peripheral corneal thicknesses were measured with ultrasonographic pachymetry. Patients were evaluated preoperatively and at 12 months postoperatively. RESULTS: Postoperative GAT measurements of IOP made from the central (13.1+/-2.7 mm Hg) and peripheral (13.9+/-3.3 mm Hg) corneal areas were significantly lower (P <0.001) than central IOP measured preoperatively (17.0+/-2.5 mm Hg). Postoperative PT measurements from the central (17.4+/-3.2 mm Hg) and peripheral (17.6+/-2.9 mm Hg) corneal areas were slightly lower than preoperative central IOP (18.4+/-2.4 mm Hg), but not statistically significant. There were no significant differences between central and peripheral IOP measurements using either method. CONCLUSION: The data demonstrate that GAT may underestimate IOP measurement, following hyperopic LASIK.
Vinciguerra, P. and F. I. Camesasca (2002). "Treatment of hyperopia: a new ablation profile to reduce corneal eccentricity." J Refract Surg 18(3 Suppl): S315-7.
PURPOSE: Hyperopic treatment normally increases corneal eccentricity (the measure of corneal asphericity). Information derived from treating corneal white scars occurring after hyperopic ablations suggests that reducing corneal eccentricity through central corneal flattening followed by smoothing eliminates scarring and prevents its recurrence. METHODS: We treated two groups of patients; Group 1 included 18 eyes of 18 patients with whitish corneal scar due either to photorefractive keratectomy (PRK) (n = 16, 88.9%) or laser in situ keratomileusis (LASIK) (n = 2, 11.1%). Mean preoperative spherical equivalent refraction was +1.20 +/- 2.30 D, and mean corneal eccentricity was +1.2 +/- 0.8. We performed phototherapeutic keratectomy (PTK) to achieve central corneal flattening and decrease corneal eccentricity, coupled with smoothing, using the Nidek EC-5000 excimer laser. Group 2 included 27 eyes of 27 consecutive patients with mean preoperative spherical equivalent refraction of +2.40 +/- 1.30 D; these patients had laser epithelial keratomileusus (LASEK) with the Nidek EC-5000 excimer laser. A new Nidek aspheric ablation profile with a wider optical zone (6.7 mm) and transition zone (9.5 to 10.00 mm) was applied. RESULTS: In Group 1 eyes, the apical scar disappeared in all eyes. Postoperative spherical equivalent refraction was +1.8 +/- 1.02 D and mean postoperative eccentricity was +0.9. In Group 2 eyes after 9 months of follow-up, mean postoperative spherical equivalent refraction was -0.30 +/- 0.30 D, with no loss of lines of BSCVA. Low corneal eccentricity values were maintained, which created a gradual change in the rate of curvature. CONCLUSIONS: The new Nidek profile for hyperopia treatment allowed successful refractive correction and maintained low eccentricity values that approached those of a normal cornea.
Hori-Komai, Y., I. Toda, et al. (2002). "Reasons for not performing refractive surgery." J Cataract Refract Surg 28(5): 795-7.
PURPOSE: To analyze the reasons that laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) were not performed in patients who requested surgical correction of their refractive errors. SETTING: Minamiaoyama Eye Clinic, Tokyo, Japan. METHODS: This retrospective review comprised 2784 consecutive patients who visited our clinic between June 1997 and August 2000. The reasons they did not receive refractive surgery (PRK or LASIK) were analyzed. RESULTS: Among the 2784 patients who requested surgery for refractive errors, 2079 patients (74.7%) had PRK or LASIK and 705 patients (25.3%) did not. The most common reasons for not treating patients surgically were myopia greater than -12.0 diopters and/or high astigmatism (20.7%), insufficient corneal thickness (8.2%), keratoconus (6.4%), cataract (5.7%), and hyperopia and/or hyperopic astigmatism (4.1%). CONCLUSIONS: Patients who request surgery have a variety of problems. Attention must be given to these individual problems, and the indications must be considered.
Odenthal, M. T., C. A. Eggink, et al. (2002). "Clinical and theoretical results of intraocular lens power calculation for cataract surgery after photorefractive keratectomy for myopia." Arch Ophthalmol 120(4): 431-8.
OBJECTIVES: To describe the refractive results of cataract surgery after photorefractive keratectomy (PRK) for patients with myopia, and to find a more accurate method to predict intraocular lens (IOL) power in these cases. DESIGN: Nonrandomized, retrospective clinical study. PATIENTS AND METHODS: Nine patients (15 eyes) who underwent cataract surgery after prior PRK to correct myopia were identified. The medical records of both the laser and cataract surgery centers were reviewed. MAIN OUTCOME MEASURES: Eight different keratometric values (K values; measured or calculated) were entered into 3 different IOL calculation formulas: SRK/T, Holladay 1, and Hoffer Q. The actual biometry and IOL parameters were used to predict postoperative refraction, which was compared with the actual refractive outcome. Also, the relative underestimation of the refractive change in corneal dioptric power by keratometry after PRK was calculated. RESULTS: In 7 of 15 eyes, IOL exchange or piggybacking was performed because of hyperopia. Retrospectively, the most accurate K value for IOL calculation was found to be the pre-PRK K value corrected by the spectacle plane change in refraction. Use of the Hoffer Q formula would have avoided postoperative hyperopia in more cases than the other formulas. The mean underestimation of the change in corneal power after PRK varied from 42% to 74%, depending on the method of calculation. CONCLUSION: The predictability of IOL calculation for cataract surgery after PRK can be improved by using a corrected, refraction-derived K value instead of the measured, preoperative K value.
Guarnieri, F. A. and J. C. Guarnieri (2002). "Comparison of Placido-based, rasterstereography, and slit-scan corneal topography systems." J Refract Surg 18(2): 169-76.
PURPOSE: Elevation-based topography systems have received growing recognition. We compared a Placido-based (EyeSys), a rasterstereography (PAR), and a slit-scan system (Orbscan) for human subjects. METHODS: Measurements were obtained from 221 eyes of 119 human subjects. We made statistical comparisons central curvature, keratometric curvatures, and meridians between the three systems. We also compared the optical pachymetry of the slit-scan system with an ultrasonic device. We analyzed cases of subclinical keratoconus, central island, photorefractive keratectomy for myopia, and hyperopia correction with arcuate keratotomy. RESULTS: The statistical comparison showed better correlation between the Placido-based and the rasterstereography systems in measurement of central curvature (R=0.95). The slit-scan system showed better correlation with the Placido system in the preoperative and postoperative radial keratotomy group (R=0.73) than in the group that included postoperative PRK eyes (R=0.69). Similar results were obtained for keratometric curvatures and meridians. The Orbscan pachymetry correlation with ultrasonic was R=0.69 and increased when the postoperative PRK eyes were excluded (R=0.95). CONCLUSIONS: Slit-projection topography and pachymetry seemed to be affected by hydration in the postoperative PRK group. The pachymetric map was useful in predicting the final outcome of refractive surgery and in the diagnosis of keratoconus.
Stevens, J. D. and L. A. Ficker (2002). "Results of photorefractive keratectomy for hyperopia using the VISX star excimer laser system." J Refract Surg 18(1): 30-6.
PURPOSE: To evaluate safety, efficacy, and predictability of photorefractive keratectomy (PRK) for hyperopic astigmatism of +1.75 to 00 D manifest refractive sphere and up to -2.50 D manifest refractive astigmatism using the VISX Star excimer laser system, version 2.5 software. METHODS: Treatment was performed on 32 eyes of 21 patients. Eighteen of 21 patients were 45 years of age or older. Manifest and cycloplegic refraction together with Pelli-Robson contrast sensitivity assessment was performed prior to surgery and 1, 3, 6, 12, and 24 months after treatment. RESULTS: Twenty-seven of 32 surgical procedures were reviewed 1 year after treatment (84%). Corneal epithelial healing was complete between day 4 and 10. Twelve months after treatment, 25 of 27 eyes (93%) achieved 20/40 or better uncorrected visual acuity and 19 eyes (70%) achieved 20/20. No patient lost two or more lines of Snellen visual acuity assessed 6 months and later after treatment. The mean spherical equivalent refraction was reduced from +2.90 at baseline to +0.10 D at 1 year and +0.40 D at 2 years; 65% of eyes had a refraction within +/- 0.50 D. Four patients had further treatment by laser in situ keratomileusis for undercorrection in three eyes and overcorrection in one eye. Pelli-Robson contrast acuity was significantly reduced 12 months after treatment from a mean 1.72 before to 1.66 after PRK (P = .02, t-test). CONCLUSIONS: PRK for hyperopia using the VISX Star excimer laser system was effective in the treatment of hyperopic astigmatism. Although no patient lost two or more lines of high contrast best spectacle-corrected Snellen visual acuity 1 year after treatment, there was a significant decrease in Pelli-Robson contrast acuity.
Dupps, W. J., Jr. and C. Roberts (2001). "Effect of acute biomechanical changes on corneal curvature after photokeratectomy." J Refract Surg 17(6): 658-69.
PURPOSE: Unintended hyperopic shift is a common yet poorly understood complication of phototherapeutic keratectomy (PTK) that raises fundamental questions about the etiology of corneal curvature change in PRK and LASIK. We investigated the relative contributions of ablation profile and peripheral stromal thickening to intraoperative PTK-induced central flattening, and propose a biomechanical model of the acute corneal response to central ablation. METHODS: Fourteen de-epithelialized eye bank globes from seven donors underwent either broadbeam ablation (approximately 100-microm depth, no programmed dioptric change) or sham photoablation in paired-control fashion. Peripheral stromal thickness changes and the pattern of thickness loss across each ablation zone were evaluated by optical section image analysis as predictors of acute corneal flattening. RESULTS: Relative to sham ablation, keratectomy caused significant anterior corneal flattening (-6.3+/-3.2 D, P = .002). Concomitant peripheral stromal thickening (+57+/-43 microm, P = .01) was a significant predictor of acute hyperopic shift (r = 0.68, P = .047). Ablation pattern bias did not consistently favor hyperopia and was a poor lone predictor of hyperopic shift. CONCLUSIONS: Unintended keratectomy-induced hyperopic shift is replicable in a human donor model and is associated with significant thickening of the unablated peripheral stroma. This biomechanical response may have a considerable impact on early refractive outcomes in PTK, PRK, and LASIK.
Bower, K. S., E. D. Weichel, et al. (2001). "Overview of refractive surgery." Am Fam Physician 64(7): 1183-90.
Patients with myopia, hyperopia and astigmatism can now reduce or eliminate their dependence on contact lenses and eyeglasses through refractive surgery that includes radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), laser thermal keratoplasty (LTK) and intrastromal corneal rings (ICR). Since the approval of the excimer laser in 1995, the popularity of RK has declined because of the superior outcomes from PRK and LASIK. In patients with low-to-moderate myopia, PRK produces stable and predictable results with an excellent safety profile. LASIK is also efficacious, predictable and safe, with the additional advantages of rapid vision recovery and minimal pain. LASIK has rapidly become the most widely performed refractive surgery, with high patient and surgeon satisfaction. Noncontact Holium: YAG LTK provides satisfactory correction in patients with low hyperopia. ICR offers patients with low myopia the potential advantage of removal if the vision outcome is unsatisfactory. Despite the current widespread advertising and media attention about laser refractive surgery, not all patients are good candidates for this surgery. Family physicians should be familiar with the different refractive surgeries and their potential complications.
Panagopoulou, S. I. and I. G. Pallikaris (2001). "Wavefront customized ablations with the WASCA Asclepion workstation." J Refract Surg 17(5): S608-12.
PURPOSE: WASCA (Wavefront Aberration Supported Cornea Ablation) is a method for wavefront-guided ablation. This new method records all existing eye aberrations with the Asclepion Wavefront Aberrometer and calculates the customized pattern for laser correction. We measured the low and high order aberrations of eyes before and after PRK and LASIK, as well as before and after flap creation. METHODS: The Asclepion Shack-Hartmann aberrometer was used to measure wavefront aberrations. Preoperative and postoperative measurements were made following both PRK and LASIK performed with conventional software, modified Aberration-free Profile (AFA) software, and specially designed WASCA software. Surgery was performed with the Meditec MEL-70 G-scan excimer laser. Additionally, measurements were made before and after flap creation only (10 eyes). RESULTS: There was a significant difference between preoperative and 1-month postoperative high order aberrations, with notable increases following conventional PRK and LASIK and less increase following modified AFA PRK and LASIK. Flap creation only changed the higher order aberrations slightly, and caused a shift toward hyperopia. In the eyes that received WASCA correction with PRK or LASIK, at 3 months postoperative the high order aberrations averaged an increase of 1.3 times for PRK and 1.8 times for LASIK. Both the AFA and WASCA treatments demonstrated improved outcomes in comparison to conventional PRK and LASIK. CONCLUSION: Wavefront mapping of the eye and wavefront-guided ablation with the Asclepion Aberrometer can be used for optimizing the results and fine-tuning visual performance after laser vision correction. WASCA PRK appeared to result in better outcomes than WASCA LASIK.
Nagy, Z. Z., R. R. Krueger, et al. (2001). "Photorefractive keratectomy for hyperopia in 800 eyes with the Meditec MEL 60 laser." J Refract Surg 17(5): 525-33.
PURPOSE: To evaluate the refractive results of 800 hyperopic eyes undergoing PRK treatment. METHODS: Eight hundred hyperopic eyes were treated with PRK. An Aesculap-Meditec MEL 60 scanning ArF excimer laser used. Treatment Group 1 consisted of eyes with a preoperative refractive error of +3.50 D or less (n = 482) and Group 2, of +3.75 D or more (n = 318). RESULTS: Preoperatively, Group 1 required an average correction of +2.88+/-1.34 D and Group 2 required +5.64+/-2.96 D. One year after PRK, average residual correction was +1.26+/-1.24 D in Group 1, and in Group 2, +2.46+/-1.84 D. In Group 1, uncorrected visual acuity (UCVA) was 20/40 or better in 88.4% (426/482); 20/20 or better in 75.7% (365); 2.1% (10/482) of eyes lost 2 lines, 2.1% (10/482) gained 2 lines; 3.1% (15/482) gained 2 or more lines of BSCVA; 74.4% (359/482) of eyes were within +/-0.50 D of target correction and 84.8% (408/482) were within +/-1.00 D. In Group 2, 47.5% (151/318) had UCVA of 20/40 or better; 34.2% (109/318) saw 20/20 or better uncorrected; 19.1% (61/318) lost 2 lines; 11.6% (37/318) lost 3 lines; none of the eyes gained 2 or more lines of BSCVA; 22.3% (71/318) were within +/-0.50 D and 46.8% (149/318) were within +/-1.00 D of target correction. Refractive stability was achieved after 6 months; a slight regression after 6 months was still observed. In Group 1, 10.5% (42/482) and in Group 2, 21.6% (69/318) complained of problems with daytime vision (glare and ghost image); during night-driving in Group 1, 17.6% (85/482) and in Group 2, 40.5% (129/318) had problems. CONCLUSION: PRK with the Aesculap-Meditec MEL 60 scanning ArF excimer laser offered the best long-term results with +3.50 D or less preoperative refractive error. With higher corrections, regression, decrease in BSCVA, and daytime visual problems were encountered.
Munger, R., A. A. Dohadwala, et al. (2001). "Changes in measured intraocular pressure after hyperopic photorefractive keratectomy." J Cataract Refract Surg 27(8): 1254-62.
PURPOSE: To investigate the effect of hyperopic photorefractive keratectomy (PRK) on intraocular pressure (IOP) measurements. SETTING: University of Ottawa Eye Institute, Ottawa Hospital, Ottawa, Canada. METHODS: In this retrospective cohort study, IOP and central corneal thickness (CCT) were measured preoperatively and at 1, 2, 3, 6, 12, 18, and 24 months in 191 eyes that had hyperopic PRK with the VISX Star excimer laser. All corrections applied were between +1.00 and +6.50 diopters (D) of sphere and less than 3.75 D of cylinder. RESULTS: At all postoperative examinations, the mean IOP in the hyperopic PRK group was 1.0 to 1.8 mm Hg lower than the preoperative IOP (P <.001). A large range of IOP changes was found across the population; eg, at 6 months, 49% of the eyes had a change in IOP from baseline of at least +/-3 mm Hg. A mean reduction of 19 microm of CCT was found with pachymetry after surgery (P < .001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or applied correction. Changes in IOP were strongly correlated with preoperative IOP at all time points and with preoperative CCT at 18 and 24 months (P < .001). After hyperopic PRK, the measured IOP was more likely to increase in patients with preoperative IOPs less than 14.5 mm Hg and more likely to decrease in patients with preoperative IOPs above 14.5 mm Hg. CONCLUSION: Changes in IOP after hyperopic PRK were similar to changes after myopic PRK, despite only minimal changes in the CCT. This suggests that hyperopic PRK results in biomechanical effects that modify the elastic properties of the cornea beyond the changes in rigidity expected from central corneal thinning. There was a strong negative correlation between the measured preoperative IOP and the change in IOP postoperatively that was likely the result of regression of the mean effect.
Nagy, Z. Z., R. R. Krueger, et al. (2001). "Photorefractive keratectomy for astigmatism with the Meditec MEL 60 laser." J Refract Surg 17(4): 441-53.
PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) in eyes treated with astigmatic refractive errors. METHODS: Nine hundred forty eyes were treated with the Aesculap Meditec MEL 60 ArF excimer laser. Treatment groups were: Group 1 (n=746) eyes with compound myopic astigmatism, Group 2 (n=104) eyes with compound hyperopic astigmatism, Group 3 (n=75) eyes treated for mixed astigmatism, and Group 4 (n=15) eyes with simple myopic astigmatism (negative cylinder). RESULTS: In Group 1, the preoperative spherical equivalent refraction of -6.10 D with an average of -1.50 D cylinder decreased to -0.95 D with -0.13 D cylinder; uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 86% (642/746 eyes); 20/20 or better in 58% (433/746 eyes); 0.8% (6/746 eyes) lost two lines of spectacle-corrected visual acuity (SCVA); 74% (552/746 eyes) were within +/-0.50 D and 93% (694/746 eyes) were within +/-1.00 D of target refraction. In Group 2, preoperative mean +4.57 D spherical equivalent refraction with an average of +1.57 D cylinder decreased to +1.13 D with +0.38 D cylinder; UCVA of 20/40 or better was achieved in 84% (87/104 eyes); 20/20 or better in 46% (48/104 eyes); 14,4% (15/104 eyes) lost two or more lines of SCVA; 52% (54/104 eyes) were within +/-0.50 D and 82% (85/104 eyes) were within +/-1.00 D of target refraction. In Group 3, mean preoperative -4.20 D cylinder and +3.00 D spherical equivalent refraction decreased to -0.50 D cylinder and -0.50 D spherical equivalent refraction; UCVA of 20/40 or better was achieved in 83% (62/75 eyes); 20/20 or better in 32% (24/75 eyes); 13.3% (10/75 eyes) lost two or more lines of SCVA. In Group 4, mean preoperative -3.98 D cylinder decreased to -0.62 D cylinder; UCVA of 20/40 or better was achieved in 60% (9/15 eyes); none of the eyes achieved 20/20 or better; SCVA remained stable in 6.6% (1/15 eyes) and decreased two or more lines in 20.0% (3/15 eyes); 20% (3/15 eyes) were within +/-0.50 D and 53.3% (8/15 eyes) were within +/-1.00 D of target refraction. CONCLUSION: PRK with the Meditec MEL 60 laser produced the best results in eyes with compound myopic astigmatism (Group 1). In all other groups, results were less predictable.
Oliver, K. M., D. P. O'Brart, et al. (2001). "Anterior corneal optical aberrations induced by photorefractive keratectomy for hyperopia." J Refract Surg 17(4): 406-13.
PURPOSE: Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye. METHODS: Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests. RESULTS: Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error. CONCLUSIONS: The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.
Seiler, T. (2001). "[Does refractive surgery really make eyeglasses superfluous?]." Schweiz Rundsch Med Prax 90(24): 1067-71.
Spectacles have become a problem of life-style in some societies. In the USA, in 1999 approximately 1 million LASIK operations have been performed to correct myopia and astigmatism and in Europe the frequency of refractive surgery stead by increases. However, only 3 to 5% of these operations are medically indicated. Refractive surgery is evaluated regarding safety and efficacy. Modern laser techniques demonstrate excellent refractive results: photorefractive keratectomy (PRK) achieved refractive success rates of 90% and more with complication rates of 0.5% and less. PRK is, therefore, a valuable technique for corrections of myopia up to -6.0 D. Similar efficacy is obtained with LASIK (laser in situ keratomileusis) in corrections up to -10 D, however, the complication rate is somewhat higher. Laser correction of hyperopia is equally successful regarding the refractive success but shows an even higher complication rate and the patient satisfaction is lower. Modern refractive laser surgery may replace spectacles in the majority of the cases, however, none of the techniques is free of complications. Therefore, we understand refractive surgery still to be inferior to the correction of ametropia by means of spectacles and any such operation should be attempted only after thorough discussion.
Wygledowska-Promienska, D., I. Zawojska, et al. (2000). "[New generation of excimer laser--Asclepion Meditec MEL 70 G-Scan]." Klin Oczna 102(5): 373-5.
The new Asclepion-Meditec MEL 70 G-Scan represents a breakthrough in surgical application of excimer laser. The laser uses the latest generation of flying spot system which utilizes a SafeScan algorithm (patent pending) to avoid corneal surface irregularities. The system utilizes a Gaussian beam profile. In cases where the cornea has regular surface, the conventional excimer laser PRK or LASIK method will provide good results. If the cornea shows an irregular surface shape, custom-tailored, topography-based ablation, which has been adapted to the corneal irregularity, should provide better results. Asclepion-Meditec have added a TSA (Tissue saving Algorithm) module to TOSCA (Topography Supported Customized Ablations) software for carrying out topography-guided corrections. This module automatically minimises the tissue removal when calculating the correction program. MEL 70 G-Scan allows to treat all forms of refractive errors, myopia and myopic astigmatism -24 D sph, -12 D cyl, hyperopia and hyperopic astigmatism +16 D sph, +8 D cyl, mixtus and irregular astigmatism.
Yi, D. H., M. Petroll, et al. (2001). "Surgically induced astigmatism after hyperopic and myopic photorefractive keratectomy." J Cataract Refract Surg 27(3): 396-403.
PURPOSE: To compare the axis and magnitude of surgically induced refractive astigmatism (SIA) after hyperopic and myopic photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA. METHODS: In this single-center retrospective study, the VISX Star S2 excimer laser was used to create a peripheral annular ablation profile to correct spherical hyperopia in 23 eyes of 16 consecutive patients. Attempted corrections ranged from +0.50 diopter (D) to +4.25 D with 0 to 1.00 D of astigmatism. The same laser was used to create a central ablation profile to correct spherical myopia in 25 eyes of 17 consecutive patients. Attempted corrections ranged from -2.25 to -6.50 D with 0 to 1.00 D of astigmatism. The absolute change in refractive astigmatism was calculated by taking the difference in magnitudes of astigmatism before and after laser treatment without regard to axis. Axis and magnitude of SIA were analyzed by vector differences. Magnitudes were compared using the Student t test, and axial shifts were compared using the chi-square test. All patients were followed for a minimum of 6 months. RESULTS: The mean changes in absolute astigmatism were 0.29 +/- 0.28 D at 3 months and 0.34 +/- 0.29 D at 6 months after hyperopic PRK and 0.40 +/- 0.35 D at 3 months and 0.39 +/- 0.36 D at 6 months after myopic PRK. The mean vectoral magnitudes were 0.49 +/- 0.29 at 3 months and 0.52 +/- 0.25 at 6 months after hyperopic PRK and 0.48 +/- 0.39 at 3 months and 0.44 +/- 0.38 at 6 months after myopic PRK. The mean values for SIA (the centroid) were 0.10 +/- 0.57 D x 113 degrees at 3 months and 0.15 +/- 0.57 D x 131 degrees at 6 months after hyperopic PRK and 0.04 +/- 0.63 D x 160 degrees at 3 months and 0.08 +/- 0.58 D x 171 degrees at 6 months after myopic PRK. There was no statistically significant difference between the 2 groups in vectoral axis or magnitude of SIA. CONCLUSION: Surgically induced astigmatism after hyperopic PRK was comparable to astigmatism induced by myopic PRK. A peripheral annular ablation for hyperopic correction, similar to a central ablation in myopic PRK, did not appear to result in uneven corneal healing causing astigmatism.
Pacella, E., S. Abdolrahimzadeh, et al. (2001). "Excimer laser photorefractive keratectomy for hyperopia." Ophthalmic Surg Lasers 32(1): 30-4.
BACKGROUND AND OBJECTIVE: Photorefractive keratectomy (PRK) has been extensively evaluated for the correction of myopia. This study was undertaken to assess the safety, efficacy, and reliability of PRK in the correction of hyperopia. PATIENTS AND METHODS: There were 28 eyes with refractions of +1 to +7.75 D treated for hyperopia with the Chiron Technolas 217-C excimer laser. Thorough visual assessments were made before treatment and at regular follow-up to 18 months. Complications and patient satisfaction were noted. RESULTS: At 18 months the mean subjective refraction was +0.46+/-1.00 D with 26 eyes (92.8%) within 1 D of emmetropia. Thirteen eyes (46.4%) achieved uncorrected visual acuity (UCVA) of 20/20 or better and all patients had an UCVA of > or = 20/32 or better. Best corrected visual acuity (BCVA) remained unchanged in 26 eyes (92.8%) and improved in 2 eyes (7.2%). On the seventh day from treatment, 17 eyes (25%) had a loss of 2 or more lines of BCVA. At 15 days this was reduced to 8 eyes (14.3%) and at one month to 3 eyes (3.6%). There were no cases of loss of 2 or more lines of BCVA at 18 months of follow-up. All patients expressed a high degree of satisfaction. CONCLUSIONS: Photorefractive keratectomy safely and effectively reduced hyperopia in the patients studied. The technique was reliable and still offered good results at 18 months of follow-up.
el-Agha, M. S., E. W. Johnston, et al. (2000). "Excimer laser treatment of spherical hyperopia: PRK or LASIK?" Trans Am Ophthalmol Soc 98: 59-66; discussion 66-9.
PURPOSE: To compare the efficacy and safety of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in the treatment of spherical hyperopia with use of the VISX STAR S2 excimer laser. METHODS: A review of 15 consecutive patients (22 eyes) receiving PRK and 22 consecutive patients (26 eyes) receiving LASIK (median follow-up, 12 months). RESULTS: Mean age was 52 +/- 7 years for patients receiving PRK and 55 +/- 9 years for patients receiving LASIK. Mean preoperative spherical equivalent was +2.25 +/- 1.16 D for PRK patients and +1.81 +/- 0.92 D for LASIK patients. Mean deviation from intended correction was -0.82 +/- 0.89 D after PRK and +0.19 +/- 0.47 D after LASIK at 1 month (P < .01); +0.16 D +/- 0.37 D after PRK and +0.29 +/- 0.51 D after LASIK at 6 months (P = .906); +0.20 +/- 0.35 D after PRK and +0.37 +/- 0.44 D after LASIK at 1 year (P = .301). At 1 year, 83.3% of PRK eyes and 61.5% of hyperopic LASIK eyes were within +/- 0.50 D of intended correction (P = 1.0). At 1 year, all eyes in both groups had acuity of 20/40 or better uncorrected, and 47.1% of PRK eyes and 54.5% of LASIK eyes had acuity of 20/20 or better uncorrected (P = 1.0). At last follow-up (minimum, 6 months), 2 eyes in each group had lost 2 lines of best spectacle-correct visual acuity, but none had lost more than 2 lines. All PRK patients experienced significant postoperative pain that required systemic medication. LASIK patients had only minor, transient discomfort. CONCLUSION: LASIK and PRK are of comparable efficacy and safety. However, PRK was associated with significant post-operative pain, an initial and temporary myopic overshoot peaking at 1 month, and stability not occurring before 6 months. LASIK was less painful and was associated with more rapid stability (at 1 month) and a trend toward better uncorrected visual acuity, although not statistically significant.
Pop, M., Y. Payette, et al. (2001). "Clear lens extraction with intraocular lens followed by photorefractive keratectomy or laser in situ keratomileusis." Ophthalmology 108(1): 104-11.
OBJECTIVE: To study photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) after clear lens extraction (CLE) with intraocular lens (IOL) implantation for hyperopia or astigmatism. DESIGN: Retrospective, noncomparative interventional case series. PARTICIPANTS: Sixty-five eyes (55 subjects) had CLE with posterior chamber IOL implants for hyperopia up to 12.25 diopters (D); 31 eyes were retreated with PRK, and 34 eyes were retreated with LASIK for residual ametropias. INTERVENTION: For PRK and LASIK, the refractive surgery was performed with the slit-scanning excimer laser Nidek EC-5000, Nidek Co., Tokyo, Japan. MAIN OUTCOME MEASURES: Manifest refraction, best-spectacle and uncorrected Snellen visual acuity, haze, and halos were evaluated before surgery and at 1, 3, 6, and 12 months postoperative. RESULTS: Forty-seven eyes were evaluated at the 12-month postoperative examination: 96% of these eyes had spherical equivalents (SE) within +/-2 D of emmetropia, 79% of eyes had SE within +/-1 D of emmetropia and 51% of eyes had SE within +/-0.50 D of emmetropia. Eighty-five percent of the eyes at 12 months postoperative had uncorrected visual acuity of 20/40 or better, and 46% of eyes had uncorrected visual acuity of 20/20 or better. Eighty-seven percent of the eyes at 12 months postoperative had uncorrected visual acuity within 1 Snellen line of their initial best spectacle-corrected visual acuity (BSCVA) before all treatment. No eye lost 2 Snellen lines of BSCVA at 3, 6, or 12 months after PRK or after LASIK. CONCLUSIONS: IOL implantation for CLE, although an invasive technique, resulted in better refractive outcomes without laser-related clinical complications after PRK or LASIK adjustment.
Haw, W. W. and E. E. Manche (2000). "Prospective study of photorefractive keratectomy for hyperopia using an axicon lens and erodible mask." J Refract Surg 16(6): 724-30.
PURPOSE: To evaluate prospectively the long-term safety, efficacy, and visual performance following photorefractive keratectomy (PRK) for hyperopia using an erodible mask and axicon lens system. METHODS: Eighteen eyes of 9 patients with a mean preoperative spherical equivalent refraction of +2.26 +/- 0.82 D (range, +1.13 to +4.00 D) underwent PRK with the Summit Apex Plus excimer laser following manual scraping of the epithelium. Eyes were prospectively evaluated 1, 3, 6, 9, 12, 18, and 24 months following the procedure. Primary outcome variables included cycloplegic refraction and uncorrected visual acuity (UCVA). Visual performance was determined by contrast sensitivity measurements under scotopic (21 lux) and photopic (324 lux) conditions and best spectacle-corrected visual acuity (BSCVA) under scotopic, photopic, and glare conditions. RESULTS: For 18 eyes, 98.2% of the mean preoperative spherical equivalent refraction was corrected to +0.04 +/- 0.87 D (range, -1.38 to +2.00 D) at 24 months after PRK. Twelve eyes (67%) were within +/-0.50 D of attempted correction and 15 eyes (83%) were within +/-1.00 D. Stability within +/-0.50 D was achieved after 6 months. Two eyes (11%) experienced almost complete regression of the refractive effect. There was no statistically significant decrease in contrast sensitivity under scotopic or photopic conditions. (P > .05). Best spectacle-corrected visual acuity showed progressive improvement in the early postoperative period. By 24 months, 0 eyes (0%) lost 2 or more lines of BSCVA under scotopic and photopic conditions and 1 eye (5.5%) lost 2 or more lines under glare conditions. Fourteen eyes (78%) had grade 1 to 3 anterior stromal haze at 24 months which was characteristically mid-peripheral and did not adversely affect visual performance. CONCLUSION: Photorefractive keratectomy with the the Summit Apex Plus excimer laser for low to moderate hyperopia resulted in an effective reduction of hyperopia without compromising long-term visual performance. Stability and recovery of distance uncorrected and best spectacle-corrected visual acuity took approximately 6 months.
Keskinbora, H. K. (2000). "Long-term results of multizone photorefractive keratectomy for myopia of -6.0 to -10.0 diopters." J Cataract Refract Surg 26(10): 1484-91.
PURPOSE: To evaluate the 4 year refractive outcome of multizone photorefractive keratectomy (PRK) in eyes with high myopia. SETTING: ++SSK Okmeydani Education Hospital, Eye Clinic, Turkiye Hospital, Okmeydani, Istanbul. METHODS: Three ablation zones were used in 92 eyes of 48 patients whose refractive errors were between -6.0 and -10.0 diopters (D) (mean spherical equivalent -7.42 D +/- 1.25 [SD]). The zones were between 4.5 and 6.0 mm based on the thickness of the cornea and the refractive correction. After the epithelium healed, dexamethasone was applied 4 times a day during the first postoperative week and then fluorometholone was applied 4 times a day for a minimum of 4 weeks. If hyperopia was found post-PRK, the steroid dose was gradually tapered. The patients were examined 1 and 3 days postoperatively, 1, 2, and 4 weeks, every 3 months for the first year, and then every 6 months. RESULTS: All patients were overcorrected in the first postoperative week. At 2 and 3 weeks, the mean manifest refraction was closer to emmetropia. At 6 months, the refraction was stable. The mean spherical equivalent was -0.10 D at the end of the first year, and stabilization continued for 4 years. After the third month, the haze regressed gradually without requiring treatment. In 1 patient, herpes simplex keratitis developed and healed in a short time with topical antiviral therapy. Nineteen eyes regressed more than -1.0 D, 4 eyes were overcorrected, 4 eyes had central islands (at 6 months), and 2 eyes were undercorrected. Two eyes were retreated for regression; 1 eye was retreated for undercorrection and 1 eye, for central island. An uncorrected visual acuity of 20/40 or better was achieved in 79.2% of eyes, and 73.9% were within +/-1. 0 D of the intended correction. CONCLUSION: ++Photorefractive keratectomy was effective in treating high myopia between -6.0 and -10.0 D. The induced refractive changes stabilized between 6 and 9 months. In most patients, no significant regression was found after this period.
Seitz, B. and A. Langenbucher (2000). "Intraocular lens power calculation in eyes after corneal refractive surgery." J Refract Surg 16(3): 349-61.
PURPOSE: The purpose of this review article is to discuss the major reasons for postoperative hyperopia after cataract surgery following radial keratotomy (RK) and photorefractive keratectomy (PRK) and to illustrate potential methods for improvement of intraocular lens (IOL) power prediction after keratorefractive surgery based on exemplary model calculations. METHODS: We previously performed model calculations in eyes after PRK for myopia (-1.50 to -8.00 D, mean -5.40 +/- 1.90 D) using keratometry readings as measured by the Zeiss keratometer and the TMS-1 topography unit and as calculated using the "clinical history method" (spherical equivalent refraction change) and change in anterior surface keratometry readings. RESULTS: We found that after PRK, mean measured keratometry readings were significantly greater than respective calculated values considering the preoperative to postoperative change of anterior corneal surface (P < .001), which itself was significantly greater than calculated keratometry readings considering the preoperative to postoperative change of spherical equivalent refraction (P < .001). IOL power underestimation correlated significantly with the difference between preoperative and postoperative spherical equivalent refraction (P = .001). CONCLUSIONS: For correct assessment of keratometric readings to be entered into more than one modern third-generation IOL power calculation formula (but not a regression formula), the clinical history method should be applied whenever refraction and keratometric diopters before the keratorefractive procedure are available to the cataract surgeon. If preoperative keratometric diopters and refraction are not known, average central power on the postoperative videokeratograph may be used after RK, but refined calculation of keratometric diopters from radius of anterior and posterior corneal surface should be used after PRK and/or LASIK.
O'Brart, D. P., C. G. Stephenson, et al. (2000). "Hyperopic photorefractive keratectomy with the erodible mask and axicon system: two year follow-up." J Cataract Refract Surg 26(4): 524-35.
PURPOSE: To evaluate efficacy and long-term stability of hyperopic photorefractive keratectomy (H-PRK) using the erodible mask and Axicon system. SETTING: Department of Ophthalmology, St. Thomas' Hospital, London, England. METHODS: Forty-three patients (43 eyes), with a mean preoperative refraction (spherical equivalent) of +4.54 diopters (D) (range +1.75 to +7.50 D), were treated using an Apex Plus(R) excimer laser (Summit Technology). This uses an erodible mask to ablate a 6. 50 mm diameter hyperopic correction and an Axicon to fashion a 1.50 mm blend zone around the correction. The overall ablation diameter was 9.50 mm. Follow-up was 2 years. RESULTS: At 2 years, the mean manifest refraction was +0.16 D (range +4.125 to -4.000 D), with the induced correction appearing stable after 9 months. Based on the Munnerlyn algorithm, predictability was acceptable for corrections up to +4.50 D, with 68% of eyes within +/-1.00 D of the predicted correction. It was poorer for +6.00 D corrections, with 33% of eyes within +/-1.00 D of that expected. Patient satisfaction was high. Forty eyes (93%) had an improvement in uncorrected near visual acuity and 37 (86%), an improvement in uncorrected distance acuity. A peripheral ring of haze, 6.5 mm in diameter, appeared in all eyes 1 month postoperatively. Its intensity was maximal at 3 to 9 months and then diminished over time. There were no significant differences in measurements of the central corneal transparency at 12 and 24 months and those preoperatively. Measurements of flicker contrast sensitivity, forward light scatter (glare), and scotopic halos showed no significant differences between preoperative values and those measured after 6 months. CONCLUSIONS: Achieved H-PRK corrections with the erodible mask and Axicon system agreed closely with the Munnerlyn algorithm, with refractive stability after 9 months. Predictability was acceptable for corrections up to +4.50 D. Axial corneal transparency was not compromised and visual performance, in terms of best spectacle-corrected visual acuity, forward light scatter, and night halos, was not impaired.
Sener, B., A. Ozdamar, et al. (2000). "Apical nodular subepithelial corneal scar after retreatment in hyperopic photorefractive keratectomy." J Cataract Refract Surg 26(3): 352-7.
PURPOSE: To report a complication, apical nodular subepithelial corneal scar, that can occur after hyperopic photorefractive keratectomy (PRK) retreatment. SETTING: Istanbul University Eye Research Center, Istanbul, Turkey. METHODS: Twelve eyes of 6 patients with apical nodular subepithelial corneal scar were retrospectively studied. Mean age of the 5 men and 1 woman was 30.2 years +/- 5.4 (SD). All eyes had hyperopic PRK retreatment for regression 9.5 +/- 1.44 months after primary hyperopic PRK. Mean spherical equivalent refraction of the residual hyperopia before retreatment was +4.67 +/- 0.81 diopters (D). All patients had a corneal haze grade of less than 1+. Hyperopic PRK retreatment was performed with a 193 nm excimer laser (Chiron Technolas Keracor 116). RESULTS: Apical nodular subepithelial corneal scars developed within the first month of hyperopic PRK retreatment and progressed until the third month in 12 eyes of 6 patients. The lesion was round and symmetrical in both eyes, smaller than 2.0 mm, and centrally located. During the mean 40.66 +/- 2.46 month follow-up, the lesion did not change in size or density. Mean spherical equivalent refraction after retreatment was 2.88 +/- 0.88 D (range +1.50 to +4.00 D) at 1 month and +4.36 +/- 1.83 D at last follow-up. Refraction was unmeasurable in 3 eyes. Five eyes lost 1 line of best spectacle-corrected visual acuity and 7 eyes, 2 or more lines. The surface regularity indexes were higher than 2.00 in all the eyes. CONCLUSION: Hyperopic PRK retreatment may cause the sight-threatening complication of apical nodular subepithelial corneal scar. This complication behaves unlike corneal haze and does not resolve spontaneously over time.
Dausch, D., E. Schroder, et al. (2000). "Topography-controlled excimer laser photorefractive keratectomy." J Refract Surg 16(1): 13-22.
PURPOSE: To assess whether photorefractive keratectomy (PRK) controlled by videokeratography can successfully treat refractive errors in eyes with corneal irregularities and improve spectacle-corrected visual acuity. METHODS: In a prospective clinical study, PRK was performed in 10 eyes of 10 patients. Reason for surgery was irregular astigmatism after penetrating keratoplasty, corneal irregularity after corneal scarring, corneal astigmatism in keratoconus, and decentration after myopic and hyperopic PRK. Excimer ablation was controlled by preoperative videokeratography (Orbscan II, Orbtek) using the MEL-70 system from Aesculap Meditec. Follow-up was 6 months. RESULTS: Concerning manifest refraction, the sphere was reduced on average from +1.92 to +0.57 D, 6 months postoperatively. Cylinder changed from -1.95 D on average to -0.30 D at 6 months postoperatively. There was improvement of uncorrected visual acuity of 2 or more lines in 5 eyes and no change in 5 eyes 6 months postoperatively. Spectacle-corrected visual acuity improved in 2 eyes by 2 to 3 lines, in 9 eyes by 1 to 3 lines, and showed no change in 1 eye. CONCLUSION: Videokeratography-controlled PRK improved refractive errors in irregular corneas with improvement of spectacle-corrected visual acuity.
Faschinger, C. W. (2000). "Phototherapeutic keratectomy of a corneal scar due to presumed infection after photorefractive keratectomy." J Cataract Refract Surg 26(2): 296-300.
This case involves a 25-year-old patient who suffered from corneal ulceration several days after photorefractive keratectomy (PRK). A central scar developed, resulting in discomfort and reduction in visual acuity. Four months later, the scar was treated by phototherapeutic keratectomy (PTK) (25 microns depth, 5 mm ablation zone). Some scar tissue was left, but it cleared slowly and steadily over the next few years. The induced hyperopia decreased from 5.00 to 1.37 diopters spherical equivalent within 28 months postoperatively. Best corrected visual acuity increased from 20/60 preoperatively to 20/20 at 28 months postoperatively. Surgeons can encourage patients with postinfectious scars after PRK to try at least 1 PTK treatment.
Jain, S. and D. J. Austin (1999). "Phototherapeutic keratectomy for treatment of recurrent corneal erosion." J Cataract Refract Surg 25(12): 1610-4.
PURPOSE: To study the role of phototherapeutic keratectomy (PTK) in the management of recurrent corneal erosion (RCE) refractory to other forms of treatment. SETTING: The Eye Department of Leicester Royal Infirmary, a tertiary referral center, Leicester, England. METHOD: A retrospective analysis of all patients who had PTK for refractory RCE between July 1994 and October 1998 was performed. The patients were recalled to determine whether they had further symptoms and whether there had been a change in their refractive error or their best corrected visual acuity. RESULTS: Seventy-seven eyes of 68 patients were treated and divided into 3 etiologic groups: trauma, 40 eyes; corneal dystrophy, 24 eyes; and no established cause (idiopathic), 13 eyes. Phototherapeutic keratectomy was combined with photorefractive keratectomy (PRK) in 6 eyes with a good result. A single treatment was performed in 71 eyes (92.2%). No significant refractive change occurred in 67.5% of eyes; 22.1% developed hyperopia (range 0 to +2.0 diopters [D]), and 10.3% developed myopia (range 0 to -1.5 D). Best corrected visual acuity was unchanged in 72.7% of eyes; 11.7% lost 1 Snellen line and 15.5% gained 1 line. There were no symptoms in 68.8% of eyes; in 31.2%, minor symptoms were noted in the morning, and these patients continued to use ocular lubricants at night. CONCLUSION: Phototherapeutic keratectomy is a safe and effective treatment for refractory RCE and, where appropriate, can be combined with PRK.
Kapadia, M. S., J. J. Genos, et al. (1999). "Epithelial scrape for photorefractive keratectomy overcorrection associated with induced regression." Cornea 18(6): 661-3.
PURPOSE: To study the effect of combined corneal epithelial scrape and contact lens wear treatment on regression in eyes with symptomatic overcorrection after photorefractive keratectomy (PRK) or PRK retreatment. METHODS: Fifteen eyes had corneal epithelial scrape with a scalpel followed by soft contact lens wear for approximately 1 month. Eight of the eyes were treated 3-4 months after the laser procedure, and seven eyes were treated >4 months after laser treatment. Fifteen eyes that had the same level of PRK correction and monitored during the same interval after PRK were used as matched control eyes. RESULTS: Epithelial scrape was performed for mean spherical equivalent (SE) of +1.1+/-0.4 diopters (D) (range, +0.50 to +1.75 D) at mean 6.1+/-3.2 months after PRK or PRK retreatment. The SE in these eyes was +0.5+/-0.6 D (range, -0.25 to +1.25 D) 3 months after epithelial scrape and +0.4+/-0.5 D (range, -0.75 to +1.25 D) 6 months after scrape. The change in scraped eyes at 3 and 6 months compared to before scrape was statistically significant (p = 0.001 and p = 0.001, respectively). The change in mean SE at 6 months after scrape (-0.7+/-0.5 D) was significantly different than the change noted in matched control eyes that were not scraped (-0.1+/-0.2 D) over the same interval after the PRK or PRK retreatment procedure. The change in SE at 6 months after epithelial scrape was greater for the eyes scraped 4 months or less (mean, 3.6+/-0.5 months) after PRK (-0.9+/-0.3 D) than eyes scraped >4 months (9.0+/-2.6 months) after PRK (-0.4+/-0.5 D). This difference approached statistical significance (p = 0.06). CONCLUSIONS: Epithelial scrape and soft contact lens treatment for symptomatic overcorrection after PRK may induce regression and is more likely to be effective when performed <4 months after the primary PRK or PRK retreatment procedure.
Stern, C. (1999). "New refractive surgery procedures in ophthalmology and the influence on Pilot's fitness for flying." Eur J Med Res 4(9): 382-4.
During the last years more and more procedures came up to render people with refractive errors possible to see without contact lenses or glasses. The different procedures for hyperopia, myopia and astigmatism are performed in increasing numbers in hospitals, laser-centres and in private practise. Modern radial keratotomy was introduced in the late 70 by the Russian Fjodorov. Because of the many complications this procedure was replaced by other procedures. Photorefractive keratectomy (PRK) was introduced in 1985, using an excimer laser to vaporize corneal tissue. Because of the side effects as pain and glare and the limited indication area Laser in situ keratomileusis (LASIK) was developed. In this procedure a corneal lamella is cut in, flapped back and the excimer laser vaporize the corneal tissue. These two procedures are mostly applied nowadays. But there are also new techniques that are still in an experimental state. One of that is the implementation of an intrastromal corneal ring that can reduce myopia up to 4 diopters. During the laser thermo keratoplasty 8 to 16 laser applications are performed in the periphery of the cornea to reduce hyperopia up to + 5 diopters. Another refractive surgery procedure is the phakic intraocular lens implantation for high myopia and +3 to +10 diopters hyperopia and the clear lens extraction with intraocular lens implantation for high hyperopia. The Joint Aviation Authority Requirements allow a hyperopia and myopia for commercial pilots of 3 diopters. Some pilot candidates with higher refractive errors undergo refractive surgery. But there are also pilots who are customers of the refractive operating ophthalmologists to get rid of the crutch glasses. This paper gives an overview about the refractive procedures that are performed nowadays on pilots and pilot candidates and gives information about the relevant indications and complications of refractive procedures in the aviation environment.
Dierick, H. G., C. E. Van Mellaert, et al. (1999). "Histology of rabbit corneas after 10-diopter photorefractive keratectomy for hyperopia." J Refract Surg 15(4): 459-68.
PURPOSE: To measure histological changes in the optical and transition zones of rabbit corneas treated with excimer laser photorefractive keratectomy (PRK) to correct hyperopia and to estimate the optical effect of these changes on the induced power profile. METHODS: Corrections of +10.00 D were ablated by means of a Questek 2620 excimer laser and rotational masks on 8 rabbit eyes. On frozen sections of 4 stained corneas and historesine sections of 4 other corneas, stromal, new stromal, epithelial, and total corneal thickness were measured on four significant locations. The optical effect of each parameter on the axial power profile was estimated in a computer simulation. RESULTS: Mean stromal regrowth was 50% of the ablated tissue. Deposition was lenticular and could account for -5.00 D of regression. Stromal thickening without regrowth occurred in the optical zone and over the shoulder, causing augmentation instead of regression. The epithelium thickened 20% in the mid-transition zone and was thinner over the shoulder, accounting for 1.00 D of regression and an increase in asphericity in the optical zone. CONCLUSION: In these hyperopic rabbit PRK corneas, stromal regrowth and epithelial hyperplasia were lenticular and contributed to regression of the optical effect. Stromal swelling around interrupted collagen lamellae seemed to occur, augmenting the optical effect. The epithelium filters high spatial frequency stromal irregularities.
Lipshitz, I., L. Fisher, et al. (1999). "Bilateral comparison of photorefractive keratectomy for myopia using two excimer lasers." J Refract Surg 15(3): 334-7.
PURPOSE: The aim of this study was to compare the results of excimer laser photorefractive keratectomy (PRK) in patients who underwent PRK using the Summit Apex (Omnimed) excimer laser in one eye and the Nidek EC-5000 excimer laser in the other. METHODS: All consecutive patients who underwent PRK with the Summit Apex laser (Omnimed) in one eye and the Nidek laser (EC-5000) in the second and had at least 12 months of follow-up were included in this retrospective study (n=30). Uncorrected and spectacle-corrected visual acuity, final spherical equivalent refraction, and grade of subepithelial haze were compared. The average preoperative spherical equivalent refraction of eyes treated with the Summit laser was -6.00 D (range, -2.50 to -8.75 D), and for Nidek-treated eyes it was -5.57 D (range, -2.50 to -8.80 D). RESULTS: Forty-seven percent of Summit-treated eyes and 53% of Nidek-treated eyes had uncorrected visual acuity of 6/6 or better; 61% of Summit-treated eyes and 63% of Nidek-treated eyes had uncorrected visual acuity of 6/7.5 or better; 95% of Summit-treated eyes and 95% of Nidek-treated eyes had uncorrected visual acuity of 6/12 or better (difference not statistically significant). Seventy-three percent of eyes treated with the Summit laser and 80% of eyes treated with the Nidek laser had a postoperative refraction within +/-0.50 D of emmetropia; 97% of Summit-treated eyes and 87% of Nidek-treated eyes had a postoperative spherical equivalent refraction within +/-1.00 D of emmetropia; the difference between the two lasers was not statistically significant. However, the percent of eyes with persistent hyperopia was smaller in the Nidek group after 3 months (P=.0062) and after 6 months (P=.07) than in the Summit group. Videokeratography was not done. CONCLUSION: Both lasers were effective with relatively low side effects. No significant difference was found between the two lasers in postoperative uncorrected visual acuity or refractive outcome. Eyes operated with the Nidek laser had less persistent hyperopia and stabilized earlier.
Bilgihan, K., F. Akata, et al. (1999). "Corneal iron ring after hyperopic photorefractive keratectomy." J Cataract Refract Surg 25(5): 685-7.
PURPOSE: To report the incidence and course of corneal iron deposition after hyperopic photorefractive keratectomy (PRK). SETTING: Gazi University, Medical School, Department of Ophthalmology, Ankara, Turkey. METHODS: Between January 1995 and December 1997, 62 eyes had PRK to correct hyperopia. RESULTS: Nine eyes developed corneal iron ring 5 to 8 months (mean 6.25 months +/- 1.3 [SD]) after PRK for hyperopia. The rings persisted during the mean follow-up of 19 +/- 11.09 months. CONCLUSION: The ring-shaped iron deposition after PRK for hyperopia must be differentiated from the Fleischer ring. Our results suggest that the slitlamp findings of peripheral corneal iron deposition in hyperopic PRK patients correlate with achieved correction.
Hosoda, Y. and K. Nakayasu (1999). "[A confocal microscopic and histological study on rabbit corneas after photorefractive keratectomy for hyperopia]." Nippon Ganka Gakkai Zasshi 103(3): 243-51.
PURPOSE: To evaluate changes in corneas after PRK (photorefractive keratectomy) for hyperopia. MATERIALS AND METHODS: Six rabbits were given PRK treatments for + 6.0 D of hyperopia. We observed these corneas by confocal microscopy at 3 days, 1 week, 2 weeks, 1 month, and 3 months after PRK, and examined them histologically. RESULTS: In the ablated area, proliferative changes in the subepithelial layer had already appeared three days after the operation. These changes progressed for one month, but had decreased at three months after operation. In confocal microscopy, the proliferative change in the subepithelial layer was observed as bright, highly refractive tissue interspersed with small spaces void of cells, and was especially evident at the wound edges of the peripheral side. The center of the cornea was slightly damaged by the excimer laser but proliferative changes were not observed there. CONCLUSION: The results of this study revealed that the damage to the center of the cornea caused by PRK for hyperopia was not very severe. But it is important to evaluate further the efficacy and safety of PRK for hyperopia.
Kourenkov, V. V., O. N. Mytiagina, et al. (1999). "Stimulating re-epithelialization after photorefractive keratectomy." J Refract Surg 15(2 Suppl): S234-7.
BACKGROUND: Re-epithelialization is usually complete in eyes 3 to 4 days following photorefractive keratectomy (PRK). However, this process is delayed in 0.5% of these eyes, leading to early development of haze. The authors investigated a method to stimulate re-epithelialization following PRK. METHODS: PRK was performed with the Nidek EC-5000 excimer laser. Following surgery, express-cytokinotherapy was applied. This method consisted of a single subconjunctival injection of 2.5 to 3.0 ml of ex juvanticus mixture of autoblood and immunomodulator Poludan. This mixture was then applied topically 4 times a day until re-epithelialization was complete. Poludan is an interferon inducer (complex polyA: polyU), stimulates expressed production of interferon and interleukin-2, and increases natural cytotoxicity. RESULTS: Thirty eyes of 30 patients with delayed re-epithelialization were treated with the described method. The average time to re-epithelialization was 7.00 + 0.64 days. Total epithelialization was complete on day 3 + 0.38 after beginning the cytokinotherapy (P < .05). Early haze developed in only 2 patients from this group. Occurrence of early haze in the control group of patients who had persistent epithelial defects 8 to 16 days postoperatively and were given traditional therapy--including corticosteroid and non-steroidal drugs--was reliably higher: 8 to 10 days (P < .01). CONCLUSION: Local express-cytokinotherapy appears to be an effective method to promote quick and complete epithelialization in eyes following PRK that experience delayed re-epithelialization. This treatment may be an important part of the prevention of early haze development and achievement of better visual acuity.
Vinciguerra, P., D. Epstein, et al. (1999). "Algorithm to correct hyperopic astigmatism with the Nidek EC-5000 excimer laser." J Refract Surg 15(2 Suppl): S186-7.
BACKGROUND: The efficacy of a new ablation algorithm for the correction of hyperopic astigmatism with the Nidek EC-5000 excimer laser was evaluated. METHODS: Twenty-five eyes with mean preoperative hyperopia of +3.76 +/- 1.70 D and a mean hyperopic cylinder of 2.20 +/- 0.80 D underwent photorefractive keratectomy (PRK) using a new algorithm with the Nidek EC-5000 excimer laser (software version 3.0). The new algorithm differed from previous algorithms in that less tissue was removed for the same amount of diopters, and there was less of a dioptric gradient between the optical zone and the transition zone. Mean preoperative spectacle-corrected visual acuity was 0.8 +/- 0.09. Minimum follow-up was 6 months. RESULTS: Mean postoperative spectacle corrected visual acuity (geometric mean) increased significantly to 0.89 +/- 0.1. The mean sphere decreased by 3.08 D and the mean cylinder by 1.60 D. CONCLUSION: Hyperopic PRK using the Nidek EC-5000 excimer laser with this new algorithm for hyperopic astigmatism appears to be safe and effective.
Vinciguerra, P., M. Sborgia, et al. (1999). "Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation." J Refract Surg 15(2 Suppl): S183-5.
PURPOSE: To assess the efficacy and safety of a combined ablation of the steep and flat meridian to correct astigmatism with the excimer laser. METHODS: Twenty-two eyes with myopic, mixed, or hyperopic astigmatism (mean preoperative spherical equivalent refraction -4.30 +/- 4.70 D [range, -12.50 to +1.50 D] and mean preoperative cylinder magnitude -3.40 +/- 1.40 D [range, -1.50 to -6.00 D]) underwent PRK with the Nidek EC-5000 excimer laser. The surgical strategy involved ablating half the amount of the cylinder (in diopters) along steepest meridian, the other half in a subsequent step along the flattest meridian; thereafter, the spherical equivalent was corrected. RESULTS: Six months postoperatively, mean spherical equivalent refraction was -0.07 +/- 0.87 D and mean cylinder was -0.44 +/- 0.36 D. Mean spectacle-corrected visual acuity was 0.86 +/- 0.13 compared to 0.75 +/- 0.22 preoperatively. Mean corneal haze was 0.67 +/- 0.31. No patient lost 2 or more lines of spectacle-corrected visual acuity and there were no complaints about night halos or glare. CONCLUSIONS: Unlike other ablation strategies, the cross-cylinder method creates a smooth transition (low dioptric gradient) between the treated and untreated cornea. This is achieved by first treating the cylinder and making the corneal surface spherical and then ablating the spherical component of the refractive error.
Seitz, B., A. Langenbucher, et al. (1999). "Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy." Ophthalmology 106(4): 693-702.
OBJECTIVE: To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, prospective, cross-sectional, clinical study. PARTICIPANTS: A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). INTERVENTION: Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). MAIN OUTCOME MEASURES: Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. RESULTS: After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P < 0.0001). On average, the relative flattening of the cornea after PRK was underestimated by 14% to 30% (maximum, 83%) depending on the method of calculation. The mean theoretical IOLP after PRK ranged from + 17.4 D (SRK/T, TOPOmeas) to +20.9 D (HAIGIS, Kcalc) depending on the calculation method for corneal power and IOLP calculation formula used. For both formulas, IOLP values using keratometric readings were significantly higher (>1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). CONCLUSIONS: To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.
Speicher, L. and W. Gottinger (1999). "Intraocular lens power calculation after decentered photorefractive keratectomy." J Cataract Refract Surg 25(1): 140-3.
A 59-year-old patient who had photorefractive keratectomy (PRK) to correct high unilateral myopia developed a progressive nuclear cataract. Phacoemulsification and intraocular lens (IOL) implantation were performed. However, determination of IOL power using automated keratometry and computerized videokeratography was not successful in this case of high axial myopia because of a decentered ablation zone, resulting in too-steep keratometric readings. Postoperative hyperopia could only be corrected by an IOL exchange. Because it may not be possible to determine the exact keratometric values for IOL calculation after PRK, subtracting the change in refraction induced by PRK from the preoperative keratometric readings might have been more accurate in this patient.
Detorakis, E. T., D. S. Siganos, et al. (1998). "Microbiological examination of bandage soft contact lenses used in laser refractive surgery." J Refract Surg 14(6): 631-5.
BACKGROUND: Disposable soft contact lenses are known to be colonized by bacteria and play a key role in bacterial keratitis pathogenesis. Such lenses, commonly used after laser refractive surgery procedures in which postoperative corneal infiltrations are sometimes observed, are potentially a substrate for bacterial inoculation. This study evaluates the extent of such a contamination. METHODS: Sixty disposable lenses collected from 60 eyes of patients who underwent photorefractive keratectomy (PRK), photoastigmatic refractive keratectomy (PARK), or laser in situ keratomileusis (LASIK) for the treatment of myopia or hyperopia were collected under sterile conditions over 4 months and cultured in various media. Results were statistically analyzed and the correlation with clinical and epidemiological data was examined. RESULTS: Eleven (18.3%) of the examined lenses were contaminated with Staphylococcus epidermidis. No other bacteria or fungi were found. Contamination was significantly more common among female patients (P = .036). Correlation with the other clinical or operative parameters examined was statistically insignificant. CONCLUSIONS: Contamination was independent of the surgical procedure and females who were frequent users of eyelid cosmetics displayed higher contamination frequencies, suggesting that bacteria possibly originate from eyelid flora. The isolation of Staphylococcus epidermidis requires close postoperative surveillance, since it is a known cause of keratitis. Prophylactic postoperative treatment with tobramycin, gentamycin, or sulphonamides could be indicated.
Kliger, C. H. (1998). "Laser thermal keratoplasty for PRK overcorrection." Ophthalmology 105(12): 2165-7.
Carones, F., R. Brancato, et al. (1998). "Photorefractive keratectomy for hyperopia using an erodible disc and axicon lens: 2-year results." J Refract Surg 14(5): 504-11.
BACKGROUND: This paper presents the results over a 2-year follow-up of the first human trial of photorefractive keratectomy (PRK) for correction of hyperopia using an erodible disc excimer laser delivery system (Summit) coupled to an axicon lens. METHODS: We treated 25 eyes of 21 patients for a mean correction of +3.38 +/- 0.97 D (range, +1.00 to +4.00 D). The hyperopic correction was made using an erodible disc inserted on the laser optical pathway; an axicon lens was then used to create a blend transition zone. Eyes were evaluated at 1, 3, 6, and 12 months after surgery. For a smaller series of 11 eyes, we also present 24-month results. RESULTS: Mean refractive error 1 month after treatment (25 eyes) was -2.35 +/- 1.55 D (range, +1.00 to -6.50 D). Eight eyes (32%) had a spectacle-corrected visual acuity loss greater than 1 line. Twelve months after treatment, mean spherical equivalent refraction was -0.47 +/- 0.80 D (range, +1.25 to -2.25 D). Nineteen eyes showed an improvement (range, 3 to 8 lines) in uncorrected distance visual acuity and 23 showed improvement in uncorrected vision at reading distance (1 to 7 lines). CONCLUSION: This technique proved effective in reducing hyperopia, but predictability must be demonstrated in a larger treatment group. Safety was confirmed by the absence of delayed reepithelialization and the absence of spectacle-corrected visual acuity loss greater than 1 line at 1 year after surgery.
Jackson, W. B., E. Casson, et al. (1998). "Laser vision correction for low hyperopia. An 18-month assessment of safety and efficacy." Ophthalmology 105(9): 1727-38; discussion 1737-8.
OBJECTIVE: This study aimed to assess the efficacy and safety of hyperopic photorefractive keratectomy (PRK) and to evaluate the effect of degree of hyperopia, two epithelial removal methods, and various postoperative patient management techniques on clinical outcomes. DESIGN: Prospective, nonrandomized, open-label clinical trial. PARTICIPANTS: A total of 38 patients with mean follow-up of 13.9 months (n = 65 eyes with hyperopia from +1.00 diopter [D] to +4.00 D) participated. INTERVENTION: Hyperopic PRK with the VISX STAR Excimer Laser System was performed. MAIN OUTCOME MEASURES: Spherical equivalent (SE) including vector analysis of SE; uncorrected visual acuity (UCVA); best-spectacle corrected visual acuity (BSCVA); low-, medium- and high-contrast visual acuities; topography; keratometry; pachymetry; and intraocular pressure, haze, and all other potential complications were measured. RESULTS: A total of 80% of eyes were within +/- 0.5 D and all but 1 eye (98%) were within +/- 1.0 D of intended manifest SE at 1 year. There was no induced astigmatism at 1 year. At 12 months, 72% of eyes had UCVA of 20/25 or better and 70% had achieved preoperative BSCVA, with no eye seeing worse than 20/25. These results remained constant at 18 months. There was a tendency toward regression between months 1 and 6 with stabilization of SEs between months 6 and 12. Thereafter, up to 18 months, there was some regression with a mean of +0.31 D, but the number of patients was small. There was one mild decentration and very slight decreases in mean intraocular pressure and central corneal thickness. One patient had grade 1.0 haze develop in both eyes at 12 and 18 months; all other patients experienced trace or no haze. There were no significant complications. CONCLUSIONS: The results of this study support the hypothesis that laser vision correction is safe and effective for treating low hyperopia. The predictability of the hyperopic laser vision correction procedure used in this study was very good. Other than the slower recovery of BSCVA and UCVA seen with this procedure, as compared with myopic PRK, there were no significant complications. The trend toward some later regression needs to be further evaluated in a larger number of patients. Overall, patients were very pleased with the treatment, even in the first 6 months.
Griffith, M., W. B. Jackson, et al. (1998). "Evaluation of current techniques of corneal epithelial removal in hyperopic photorefractive keratectomy." J Cataract Refract Surg 24(8): 1070-8.
PURPOSE: To determine the efficacy of 3 current methods used to remove corneal epithelium prior to photorefractive correction of hyperopia and to compare clinical data in patients who had rotary brush or blunt scrape epithelial removal in the treatment of hyperopic photorefractive keratectomy (PRK). SETTING: University of Ottawa Eye Institute, Ottawa General Hospital, Ottawa, Ontario, Canada. METHODS: The epithelium from human eye-bank eyes was removed using a Paton spatula, 15% alcohol, and the Amoils rotating plastic brush. The effects were examined by scanning and transmission electron microscopy. Twelve month postoperative data were obtained on 25 eyes with refractions of +1.00 to +4.00 diopters (D) that had been treated for hyperopia with the VISX Star excimer laser, using blunt scrape or the rotary brush to remove the corneal epithelium. RESULTS: All 3 methods effectively removed corneal epithelium. The Paton spatula, however, left small nicks in Bowman's layer. Both the rotating brush and alcohol debridement left Bowman's layer intact. Alcohol treatment required follow-up epithelial debris removal, while brushing left minimal amounts of debris. There was a strong trend toward rapid epithelial healing in the brushed corneas compared with the scraped ones, but this was not statistically significant. Clinically, at 12 months postoperatively, brushed corneas showed a trend toward more superior outcomes than scraped corneas in actual refractive outcome, uncorrected visual acuity (UCVA), lines of UCVA gained, and predictability of the desired outcomes. However, only the outcome in UCVA of 20/40 or better and the decreased incidence of haze in the brushed corneas over scraped ones were statistically significant. CONCLUSIONS: Both alcohol and the rotating brush provide a quick, effective means of removing the corneal epithelium with minimal risk of damage to Bowman's layer. In our experience, the brush technique was as effective as and possibly superior to the blunt scrape for epithelial removal in hyperopic PRK.
Alio, J. L., A. Artola, et al. (1998). "Complications of photorefractive keratectomy for myopia: two year follow-up of 3000 cases." J Cataract Refract Surg 24(5): 619-26.
PURPOSE: To evaluate the results and complications of photorefractive keratectomy (PRK) for myopia. SETTING: Alicante Institute of Ophthalmology, University of Alicante, Spain. METHODS: This prospective study evaluated the results and complications of the first 3000 cases of PRK performed with a VISX Twenty-Twenty excimer laser. Myopia ranged from -1.0 to -14.0 diopters (D) and astigmatism, from -1.0 to -5.0 D. Follow-up was 2 years. RESULTS: Ten eyes (0.7%) lost two or more lines of best corrected visual acuity 1 year after surgery. Retreatment for undercorrection or regression was done in 7.41% in the low myopia group and 38.69% in the high myopia group. Central islands, which could be detected only on videokeratoscopy, occurred frequently but influenced the refractive and visual outcomes in few cases. Severe haze was present in 17 eyes only after 1 year follow-up. There were no cases of progressive hyperopia. Other complications such as eccentric ablation producing astigmatism (n = 15), delayed re-epithelialization, or recurrent corneal erosion were rare. CONCLUSION: There were few complications after PRK in 3000 eyes. With proper patient selection, PRK can be considered relatively safe compared with other refractive procedures.
Pop, M. (1998). "Laser thermal keratoplasty for the treatment of photorefractive keratectomy overcorrections: a 1-year follow-up." Ophthalmology 105(5): 926-31.
OBJECTIVE: To evaluate the results of holmium:YAG laser thermal keratoplasty (LTK) treatment for overcorrection of myopia after a photorefractive keratectomy (PRK) treatment. PARTICIPANTS: Thirty-six eyes (33 patients) were treated with a nontouch holmium:YAG laser (Sunrise Technologies, Model LTK, Freemont, CA) because of hyperopia (mean +/- standard deviation of +2.06 diopter [D] +/- 0.75, ranging from +1.0 to +3.5 D) following a PRK treatment. A control LTK group treated for primary hyperopia, who had preoperative refraction values not statistically different from the PRK + LTK group, was used for comparison. INTERVENTION: The number of spots applied varied from 8 to 24, and the energy used was 200 to 240 mJ. A maximum of three rings of four to eight spots were placed between 6 and 8 mm from the visual axis. RESULTS: Twelve months after the LTK retreatment for PRK patients, mean refraction was +1.14 D +/- 1.09. Regression from 1 to 12 months was 0.5 D +/- 1.1. At 12 months, 50% of eyes were within 1 D of emmetropia; 93% of eyes had uncorrected visual acuity (UCVA) of 20/40 or better; and 24% of eyes had UCVA of 20/20 or better. Refraction was not stable for 11 eyes (34%) that regained original sphere values or higher. Best-corrected visual acuity was not affected, and haze was not increased nor decreased by the procedure. CONCLUSIONS: Twelve months after an LTK retreatment for an initial PRK, two thirds of the retreated eyes did not need further retreatments. However, clinical data showed that LTK should be kept for +1 to +2 D of hyperopia for PRK overcorrection retreatments.
Vinciguerra, P., D. Epstein, et al. (1998). "Long-term results of photorefractive keratectomy for hyperopia and hyperopic astigmatism." J Refract Surg 14(2 Suppl): S183-5.
PURPOSE: This study was conducted to determine the safety and efficacy of using the Nidek EC-5000 excimer laser for photorefractive keratectomy to correct hyperopia and hyperopic astigmatism. METHODS: We treated 67 eyes of 44 patients for hyperopia and hyperopic astigmatism with the Nidek EC-5000 excimer laser. The algorithm provided an ablation zone of 5.5 mm diameter with the addition of a tapered transition zone of 3.5 mm diameter, for a total ablation of 9 mm diameter. RESULTS: Uncorrected visual acuity (geometrical mean) changed from 0.16 to 0.37 at 12 months; corrected visual acuity (geometrical mean) changed from 0.8 to 0.89; mean sphere decreased by 2.08 D from 3.76 to 1.40 D (range, 1.70 to 1.68 D) and cylinder by 1.40 D from 2.20 to 1.00 D. Refractive results for < or = 3.00 D were reasonably accurate and stable, but for > +3.00 D, undercorrection and regression over l year were the rule. CONCLUSION: Hyperopic PRK proved to be a safe technique in regard to the risk of loss of visual acuity with no central corneal opacities and with a generally rapid recovery of baseline spectacle-corrected visual acuity, but the predictability of correction greater than +3.00 needs improvement.
Shah, S., A. Chatterjee, et al. (1998). "Epithelial debridement for secondary hyperopia following myopic excimer laser photorefractive keratectomy." J Cataract Refract Surg 24(1): 31-4.
BACKGROUND: To evaluate epithelial debridement for the treatment of persistent hyperopia in eyes that had photorefractive keratectomy (PRK). SETTING: Optimax Laser Eye Clinics, Manchester, London, Bristol, England. METHODS: Epithelial debridement was performed on 46 eyes to reduce the hypermetropia following excimer laser PRK. RESULTS: Mean age of the patients was 43 years +/- 9.7 (SD). Mean refractive change was -0.51 diopter (D) +/- 0.76 (range +0.75 to -2.50 D). Mean change in best corrected visual acuity (BCVA) was 0.00 Logmar units (range +0.40 to -0.20 units), although 33% of eyes lost one line or more of Logmar BCVA. Mean follow-up after debridement was 61.0 +/- 26.9 weeks (range 26 to 140 weeks). CONCLUSIONS: Epithelial debridement is an unpredictable procedure to treat secondary hyperopia after PRK, producing a small mean change in spherical equivalent with a wide range of results. A significant number of eyes lost one line or more of Logmar BCVA. We therefore do not advocate epithelial debridement after PRK.
Sener, B., A. Ozdamar, et al. (1997). "Photorefractive keratectomy for hyperopia and aphakia with a scanning spot excimer laser." J Refract Surg 13(7): 620-3.
OBJECTIVE: To study the safety, efficacy, predictability, and stability of photorefractive keratectomy (PRK) for hyperopia and aphakia. METHODS: Fifteen eyes of 15 patients (mean age, 33 +/- 5.95 yrs) were enrolled in the study and divided into three groups. The first group was comprised of six eyes that had hyperopia ranging from +1.75 to +4.75 D; the second group had seven hyperopic eyes ranging from +5.00 to +9.75 D; the third group included two eyes of two aphakic patients. All eyes had PRK with a 193 nm argon fluoride excimer laser (Chiron-Technolas, Keracor 116) with a 10 Hz repetition rate and a fluence of 120 mJ/cm2. The total follow-up time in all eyes was 12 months. RESULTS: In the lower hyperopia group, 0% eyes were within +/- 0.50 D and 66% (N = 4) of eyes were within +/- 1.00 D of emmetropia with the other two eyes between +1.00 and +2.00 D at 1 year after PRK. In the higher hyperopia group, all eyes had at least +3.00 D of hyperopia at 1 year. In the aphakic group, both eyes achieved less than 50% of the target correction of +10.00 D at 1 year. Final uncorrected visual acuity ranged from 20/20 to 20/30 in the lower hyperopia group, 20/30 to 20/50 in the higher hyperopia group, and count fingers in the aphakic group. CONCLUSIONS: PRK is a relatively safe, stable, and effective procedure with reasonably good predictability for eyes with less than +5.00 D of baseline hyperopia, and poor predictability for eyes with more than +5.00 D of baseline hyperopia. PRK is ineffective in the correction of aphakia.
Heng, W. J., W. K. Chan, et al. (1997). "Photorefractive keratectomy for the treatment of compound myopic astigmatism using the ablatable mask." Ann Acad Med Singapore 26(4): 401-4.
Eight eyes of 8 patients with compound myopic astigmatism were treated with excimer laser photorefractive keratectomy (PRK) using a hand-held ablatable mask in conjunction with the Summit excimer laser. The attempted correction ranged from -1.25 to -400 dioptres (D) of astigmatism and 0 to -8.00 D of myopia. All eyes had attained at least 6 months of postoperative follow-up. Five of the 8 eyes achieved an unaided visual acuity of 6/12 or better. Postoperative refractions ranged from -0.50 to -3.50 D of refractive cylinder and from +0.50 to -3.75 D of spherical error. Decentration of the ablation zone was encountered in 3 eyes due to shifts in patients' fixation. Technical difficulty with the use of the hand-held ablatable mask limited the widespread application of this procedure and it has now been superseded by newer excimer laser systems which can correct astigmatism without having to employ a mask. Despite this, because of the theoretical ability of the mask to correct any form of refractive error, the concept of the mask shape transfer process will remain as a potential alternative in refractive surgery, especially for correction of hyperopia and hyperopic astigmatism.
Bilgihan, K., F. Akata, et al. (1997). "Photorefractive keratectomy in refractive accommodative esotropia." Eye 11 ( Pt 3): 409-10.
Photorefractive keratectomy (PRK) was performed on a 19-year-old man with hyperopic astigmatism and refractive accommodative esotropia. The patient was orthophoric while wearing spectacles, but had an esotropia of 30 prism dioptres at near and distance vision without spectacles. The best corrected visual acuity of the right eye was 20/50 and of the left eye was 20/20. The excessive accommodative convergence of the patient was eliminated by correcting the hyperopic refractive error by performing PRK, and the patient became orthophoric after the treatment.
Tappouni, F. (1997). "Experience with PRK for hyperopia." J Cataract Refract Surg 23(7): 973-4.
Pietila, J., P. Makinen, et al. (1997). "Excimer laser photorefractive keratectomy for hyperopia." J Refract Surg 13(6): 504-10.
OBJECTIVE: Excimer laser photorefractive keratectomy (PRK) has been shown to be an effective method in the treatment of refractive errors, especially myopia. We evaluated prospectively the efficacy, predictability, stability, and safety of excimer laser PRK in the treatment of hyperopia. METHODS: Thirty-four hyperopic eyes were treated with an Aesculap-Meditec (MEL 60) excimer laser. The patients were divided into two groups. In the low-moderate hyperopia group, baseline spherical equivalent refraction was between +1.50 and +6.00 diopters (D) (mean, +4.20 +/- 1.30 D) and in the high hyperopia group between +6.25 and +9.75 D (mean, +7.70 +/- 1.30 D). Follow-up visits occurred 1, 3, 6, and 12 months after surgery. RESULTS: One-year results were available for a total 27 eyes (79%): 15 eyes with low to moderate hyperopia and 12 eyes with high hyperopia. One year after PRK in the low-moderate group, six eyes (40%) had a refractive error within +/- 1.00 D of emmetropia, but in the high hyperopia group only two eyes (17%) were within +/- 1.00 D of emmetropia; three eyes (20%) and one eye (8%) were within +/- 0.50 D, respectively. The stability of the refractive change was better in the low to moderate hyperopia group; in the high hyperopia group there was still some regression after 6 months. At 12 months, 10 eyes (67%) in the low-moderate and one eye (8%) in the high hyperopia group had postoperative uncorrected visual acuity of 20/40 or better. One eye in the low-moderate hyperopia group saw 20/20 without correction. Only one eye lost two lines of spectacle-corrected visual acuity. Haze was more intense in the high hyperopia group, but it did not reduce visual acuity. No vision-threatening complications were observed. CONCLUSIONS: When low to moderate hyperopia up to +6.00 D is treated, excimer laser PRK with the Aesculap Meditec MEL60 laser is safe and moderately effective, and refraction stabilizes after 3 months in most eyes. However, PRK is not sufficient to treat high hyperopia in an effective and predictable way.
Kaminski, S. and J. Lukas (1997). "[Refractive laser surgery of the cornea]." Wien Med Wochenschr 147(12-13): 302-7.
The importance of refractive corneal laser surgery is increasing. Since the introduction of the Excimer laser in 1990 approximately 350.000 eyes were treated worldwide until the end of 1996. Postoperative refraction is mainly determined by the amount of intended correction: correction of myopia of up to -6 dpt using photorefractive keratectomy (PRK) has a success rate surpassing 93%, in higher myopic corrections the success rate drops to 30%. The complication rate is also directly related to the amount of correction: with corrections of up to 6 dpt it reaches up to 3% and in corrections of over 9 dpt manifest scars occur in more than 10%. Better results in myopias over -7 dpt are achieved using the laser in situ keratomileusis (LASIK), which is a combination of lamellar corneal surgery and the excimer laser. With LASIK the complication rate in corrections of up to 6 dpt is higher compared to PRK. The correction of hyperopia has still a fairly low success rate with both techniques that we suppose hyperopia to be a relative contraindication for corneal laser surgery.
Goggin, M. and F. Lavery (1997). "Holmium laser thermokeratoplasty for the reversal of hyperopia after myopic photorefractive keratectomy." Br J Ophthalmol 81(7): 541-3.
BACKGROUND: Overcorrection following myopic photorefractive keratectomy, with a target of emmetropia, leaving a spherical equivalent of more than 1.0 D of hyperopia is of the order of 1%. This study analyses the efficacy, safety, and 1 year stability of outcome of laser thermokeratoplasty (LTK) carried out on eyes with persistent symptomatic hyperopia following photorefractive keratectomy (PRK) for myopia. METHOD: 11 consecutive eyes in 11 patients underwent LTK using the Technomed Holmium 25, contact holmium:YAG laser system. The mean spherical equivalent before LTK was +2.06 D (SD 1.02 D, range +1.00 D to +4.75 D) based on a non-cycloplegic refraction. Between four and 16 burns were used per eye, depending on the error to be corrected. RESULTS: The mean spherical equivalent was +0.511 D (SD 0.551) at 1 year. Ten of the 11 eyes were seeing 6/12 or greater, unaided (91%) and nine were within 1.0 D of the target sphere equivalent (82%). Recovery of unaided acuity occurred during the first week in four cases and the first month in the rest. One eye lost greater than one line of best corrected vision (9%), going from 6/5 to 6/7.5 and one gained a line (9%), 6/12 to 6/7.5. No complications occurred during the follow up period. CONCLUSIONS: In this study of a small number of eyes with hyperopia induced by PRK, LTK appears safe, predictable, and stable for low errors followed for 1 year.
Venter, J. A. (1997). "Photorefractive keratectomy for hyperopia after radial keratotomy." J Refract Surg 13(5 Suppl): S456.
BACKGROUND: Progressive hyperopia is a common complication following radial keratotomy. METHODS: Ten eyes of ten consecutive patients with hyperopia after radial keratotomy between +1.75 and +4.00 diopters (D) were treated with the hyperopia module of the Nidek Model EC-5000 excimer laser. The mean preoperative uncorrected visual acuity was 0.38 (20/60+). RESULTS: After excimer laser photorefractive keratectomy (PRK), mean uncorrected visual acuity improved to .72 (20/30+). No complications occurred with the exception of one eye with haze greater than 2+. CONCLUSION: PRK for hyperopia is a valuable method for correcting hyperopia after radial keratotomy.
Ojeimi, G. and N. Waked (1997). "Laser in situ keratomileusis for hyperopia." J Refract Surg 13(5 Suppl): S432-3.
PURPOSE: To study the efficacy of laser in situ keratomileusis (LASIK) for hyperopia. METHODS: We performed LASIK on 21 eyes using the Nidek EC-5000 excimer laser with software version 2.18 AH. The Chiron Automated Corneal Shaper was used to create the flap. Retreatments were needed in seven eyes due to decentration or undercorrection. RESULTS: Although a high rate of satisfaction was noted among patients, complications were encountered such as decentration (three eyes), undercorrection (four eyes); one patient progressed to low myopia with a loss of spectacle-corrected visual acuity and one patient had regression 3 months after the initial LASIK. CONCLUSION: Although this technique has several advantages over other techniques (holmium, ALK, PRK, hexagonal RK), it has a high rate of retreatment and some complications. Software refinement is needed, and patients should be adequately informed about what to expect from this technique.
Jackson, W. B., G. Mintsioulis, et al. (1997). "Excimer laser photorefractive keratectomy for low hyperopia: safety and efficacy." J Cataract Refract Surg 23(4): 480-7.
PURPOSE: To assess the safety and efficacy of photorefractive keratectomy (PRK) to correct low hyperopia. SETTING: University of Ottawa Eye Institute, Ottawa General Hospital, Ontario, Canada. METHODS: Twenty-five eyes with refractions of +1.00 to +4.00 diopters (D) and cylinder of 1.00 D or less were treated for hyperopia with the VISX Star excimer laser system using a refined ablation architecture. Thorough visual assessments were performed preoperatively (baseline) and 1, 3, and 6 months postoperatively. Complications were recorded and the level of patient satisfaction was noted. RESULTS: Mean spherical equivalent at 6 months was +0.27 D +/- 0.55 (SD), which was an 89% reduction over baseline. Eighty-four percent of patients gained two to seven lines of near uncorrected visual acuity (UCVA) and 1 patient (4%) lost more than one line. Eight percent achieved 20/25 or better UCVA. Approximately half realized their preoperative distance best corrected visual acuity (BCVA) by 1 month. By the end of the study, all patients had improved, achieved, or were within one line of their baseline distance BCVA. There were some slight reductions in lower contrast acuity at 6 months, although dim lighting conditions did not further reduce these acuities. Most patients had no clinically meaningful change in cylinder. The most common complications included early, transient corneal surface irregularities and visual symptoms and trace haze (grade < or = 0.5) in 14 of 23 patients at 6 months. All but 1 patient expressed a high degree of satisfaction. CONCLUSIONS: These results support the hypothesis that PRK shows great promise as a safe and effective treatment for low hyperopia. There were no significant complications and no decentered ablations. The slight regression occurred with or without the presence of trace haze. Overall, refractive stability was encouraging, although longer follow-up is needed.
Dausch, D., Z. Smecka, et al. (1997). "Excimer laser photorefractive keratectomy for hyperopia." J Cataract Refract Surg 23(2): 169-76.
PURPOSE: To achieve less variation in the refractive outcome of hyperopic photorefractive keratectomy (PRK) by enlarging the treatment zone to 9.0 mm. SETTING: Marienhospital, Amberg, Germany, and Klinika Ocni A Esteticke Chirurgie, Zlin, Czech Republic. METHODS: This prospective clinical study was based on the results of PRK in 68 hyperopic eyes (62 patients) using an MEL 60 excimer laser. Mean attempted correction was +4.85 diopters (D) +/- 1.45 (SD) (range +2.00 to +8.25 D). Maximum follow-up was 12 months (68 eyes). RESULTS: One year after PRK, 55 eyes (81%) were within 1.00 D and 40 eyes (59%) were within 0.50 D of the intended correction (predictability). Best corrected visual acuity was unchanged or improved in 62 eyes (92%) (safety). Four eyes (6%) lost one line, 1 eye (1%), two lines, and 1 eye (1%), three lines. Sixty-six eyes (97%) had an uncorrected visual acuity of 20/40 or better (efficacy) and 27 (40%), 20/20 or better. CONCLUSION: Photorefractive keratectomy with a 9.0 mm treatment zone was an efficient and relatively safe procedure for correcting hyperopia of up to 8.25 D. The predictability was good. Great care must be taken to improve the centration of the optical zone.
Alio, J. L., M. M. Ismail, et al. (1997). "Correction of hyperopia induced by photorefractive keratectomy using non-contact Ho:YAG laser thermal keratoplasty." J Refract Surg 13(1): 13-6.
PURPOSE: To evaluate the safety and effectiveness of non-contact holmium:YAG laser thermal keratoplasty in correcting hyperopia induced by photorefractive keratectomy (PRK). METHODS: Non-contact holmium:YAG laser thermal keratoplasty was applied to 14 eyes with significant hyperopia induced by PRK. The mean spherical equivalent refraction before holmium:YAG laser thermal keratoplasty was +4.20 +/- 1.80 diopters (D) (range, +1.75 to +6.25 D). The results were evaluated 12 months after holmium:YAG laser thermal keratoplasty. RESULTS: No sight-threatening complications occurred. Recovery of spectacle-corrected visual acuity took from 2 to 6 weeks. The immediate significant myopic shift that developed in all eyes gradually receded over 6 to 8 weeks. All eyes were relatively stable after 9 months. At 12 months, there was no statistically significant difference (p < .005) between the mean preoperative spectacle-corrected visual acuity (0.71 +/- 0.12) and the mean postoperative uncorrected visual acuity (0.65 +/- 0.28). At 12 months there was a mean increase of 4.60 +/- 1.20 D in central keratometric power. Total regression did not occur in any eye. CONCLUSIONS: Non-contact holmium:YAG laser thermal keratoplasty offers a safe and effective alternative to correct PRK-induced hyperopia.
Dierick, H. G., C. E. Van Mellaert, et al. (1996). "Topography of rabbit corneas after photorefractive keratectomy for hyperopia using airborne rotational masks." J Refract Surg 12(7): 774-82.
PURPOSE: To determine the long-term outcome of photorefractive keratectomy (PRK) for hyperopia on the rabbit cornea using ablation profiles with a smooth transition zone. METHODS: Two profiles were ablated by means of an excimer laser and rotational masks, each profile on four rabbit eyes. Corrections of +10 diopters (D) were planned in all operations. The right eye was treated with a 4-mm optical zone and a 2-mm transition zone (4-mm/8-mm profile), the left eye with a 4-mm ablation and a 1-mm transition zone (4-mm/6-mm profile). Corneal topography was measured with an EyeSys videokeratoscope at 3, 10, 20, 30, 40, 50, 65, 75 and 120 weeks postoperatively. RESULTS: After more than 2 years the axial power-not corrected for the physiologic flattening of the corneas-showed a residual steepening of +3.60 (+/-3.90) D for the right eyes and +3.9 (+/-2.8) D for the left eyes. The diameter of the topographic optical zone was equal to or smaller than the innermost mire. The power started to decrease paracentrally, giving the profile graph of the power a characteristic peak pattern. The flat transition zone, typical of PRK for hyperopia, could be recognized on the Placido images as a characteristic broadening of the midperipheral rings. The axial power map and the power profile did not show this flattening in the transition zone. CONCLUSION: A steepening of the central cornea by PRK is possible. The diameter of the topographic optical zone of homogeneous power is smaller than induced, increasing considerably the asphericity of the central cornea. The 4-mm/8-mm ablation profiles did not give a larger diameter topographic optical zone nor less regression than the 4-mm/6-mm ablation profiles. The videokeratoscope makes errors in measuring axial power of mixed convex-concave surfaces.
Mader, T. H., C. L. Blanton, et al. (1996). "Refractive changes during 72-hour exposure to high altitude after refractive surgery." Ophthalmology 103(8): 1188-95.
PURPOSE: The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK). METHODS: The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level. RESULTS: Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level. CONCLUSIONS: Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.
Gauthier, C. A., P. Fagerholm, et al. (1996). "Failure of mechanical epithelial removal to reverse persistent hyperopia after photorefractive keratectomy." J Refract Surg 12(5): 601-6.
BACKGROUND: Residual hyperopic overcorrection after photorefractive keratectomy (PRK) using early algorithms is a rare but serious complication. Anecdotal evidence suggests that epithelial removal can stimulate epithelial hyperplasia, thereby reducing overcorrection. The aim of this study was to determine if epithelial removal effectively reduced hyperopia after PRK for myopia and, concurrently, to correlate the healing response with the refractive outcome. METHODS: Enrolled were seven eyes of seven patients (mean age, 44 +/- 13 years) who had undergone PRK with a mean manifest refractive error of +2.21 +/- 0.74 diopters (D). All had undergone PRK an average of 24 +/- 9 months previously. Epithelial removal was performed over the excimer-treated zone with a surgical blade. Subjective refraction, epithelial thickness, corneal topography, and subepithelial haze were measured up to 1 year postoperatively. RESULTS: Reduction in hyperopia between the baseline and 1-year visit was not statistically significant (mean difference, 0.55 D reduction; p = .102). That epithelial removal did not stimulate a wound-healing response is further supported by the absence of change in epithelial thickness over the first month and the small amounts of subepithelial haze. Central corneal power was reduced by a mean of 0.64 D after 1 month (p < .05). CONCLUSIONS: Epithelial removal alone did not reduce the hyperopic overcorrection present after PRK, nor did it stimulate epithelial hyperplasia in the majority of these eyes. However, a trend toward improvement was noted with time was noted.
Gauthier, C. A., B. A. Holden, et al. (1996). "Role of epithelial hyperplasia in regression following photorefractive keratectomy." Br J Ophthalmol 80(6): 545-8.
AIM--To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK). METHODS--Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed. RESULTS--The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001). CONCLUSIONS--Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression.
Tutton, M. K. and P. M. Cherry (1996). "Holmium:YAG laser thermokeratoplasty to correct hyperopia: two years follow-up." Ophthalmic Surg Lasers 27(5 Suppl): S521-4.
BACKGROUND AND OBJECTIVE: Treatment of hyperopia is more of a challenge than PRK but the development of the holmium:YAG laser has provided a more controlled way of carrying out laser thermokeratoplasty (LTK). PATIENTS AND METHODS: Twenty two eyes with hyperopia were treated with a Summit Technology OmniMed holmium laser by placing two rings of eight laser spots at 6.5 and 9 mm (centred on the visual axis) to produce a 4.00 diopters (D) correction. RESULTS: An average +2.10 D refractive correction was achieved in the 17 eyes with no induced astigmatism with an accuracy of 25% within 1.00 D, 60% within 2.00 D and 100% within 3.00 D. However, significant astigmatism (+1.25 to +2.5 Dcyl) was produced in 23% of eyes from 6 months post-laser and these required astigmatic LTK correction. CONCLUSIONS: The overall results were disappointing in that there was an approximate 50% regression at two years post-LTK. However, the rate of regression was very slow at 24 months, and most patients remarked how well they could see in the first few months following the treatment.
Migden, M., B. S. Elkins, et al. (1996). "Phototherapeutic keratectomy for corneal scars." Ophthalmic Surg Lasers 27(5 Suppl): S503-7.
BACKGROUND AND OBJECTIVE: Phototherapeutic keratectomy (PTK) is an effective method of treating a variety of corneal disorders. We report our experience in using PRK to treat corneal scars. PATIENTS AND METHODS: We retrospectively analyzed the data from a cohort of 22 eyes with corneal scars. The etiology of the scar was recorded for each patient. The change in best corrected visual acuity, spherical equivalent, and astigmatism were evaluated at one and three months after surgery. RESULTS: At three months, seven of 18 eyes (39%) had improved 2 or more lines of best corrected visual acuity and 3 eyes (16%) had lost 2 or more lines. Eleven of 18 eyes (61%) had a hyperopic shift of more than 1.00 diopter (D) and eight of 18 eyes (44%) had a hyperopic shift of more than 2.00 D. There was a mean reduction in astigmatism of 0.67 +/- 4.00 D. Four of eight eyes with traumatic scars had significant improvement as compared to none of five eyes with infectious scars. CONCLUSION: PTK is a relatively safe and effective means of treating corneal scars and thereby may offer an alternative to corneal transplantation.
Cherry, P. M. (1996). "Treatment of astigmatism associated with myopia or hyperopia with the holmium laser: second year follow-up." Ophthalmic Surg Lasers 27(5 Suppl): S493-8.
BACKGROUND AND OBJECTIVE: In 1993, the Summit Technology apogee system for treating astigmatism was not available, so (to avoid the deep cuts of astigmatic keratotomy) the Summit Holmium: YAG laser was used to treat astigmatism associated with myopia; an excimer laser photorefractive keratectomy was to be performed when the keratometry readings had stabilized. The holmium:YAG laser also was utilized to concurrently treat hyperopia and astigmatism. PATIENTS AND METHODS: For myopic astigmatism, four holmium spots were administered, two on either side of the optical zone. An optical zone of 6.5 mm was used for keratometric astigmatism of 4.00 diopters (D) or greater; 7.0 mm for 3.00 to 3.90 D; 7.5 mm for 1.50 to 2.90 D. For hyperopic astigmatism, two extra spots were placed in the inner treatment ring, one on either side of the flattest meridian for 1.50 to 2.90 D of keratometric astigmatism. By omitting the outer ring treatments in the steeper meridian and using four extra spots, two on either side of the flattest meridian in the inner ring, 3.00 D or more was treated. RESULTS: Thirty-one myopic eyes were treated; five were lost to follow-up; 12 have subsequently had a photoastigmatic refractive keratectomy (PARK); six have had a PRK; eight had had no further procedures. Seven eyes now have 18 months of follow-up or more (and have not had a PARK); the four successes are presented in detail and it appears that their keratometry readings are nearly stable. CONCLUSION: Four of 7 (57%) myopic eyes, which had holmium laser treatment of associated astigmatism, can be considered as successes after 18 months or more follow-up. Keratometry readings are nearly stable; further follow-up is required to determine if regression continues. The treatment of astigmatism simultaneously with hyperopia treatment with the holmium laser was not successful.
Castanera, J. (1996). "Topographic comparison of monozone, multipass and multizone ablations for myopic photorefractive keratectomy." Ophthalmic Surg Lasers 27(5 Suppl): S471-6.
BACKGROUND AND OBJECTIVE: Multizone and multipass ablation techniques have been developed in an attempt to improve results over monozone photorefractive keratectomy (PRK). This study was conducted to evaluate the results obtained in the treatment of myopia with multizone PRK in comparison with monozone ablation in low myopia, and with multipass ablation in high myopia. PATIENTS AND METHODS: Sixty-two eyes with low myopia (-1.90 to -6.25 diopters [D]) were divided into two groups: 42 eyes were treated with a 5.0 mm monozone ablation and compared with 20 eyes treated with a multizone software using 5.0-5.7-6.5 mm optical ones and a 100-60-40% algorithm. Thirty-four eyes with high myopia (-6.50 to -12.00 D) were also divided into two groups: 17 eyes were treated with a multipass technique dividing the attempted correction in three successive treatments with 5.0-6.0-6.5 mm optical zones and 50-30-20% of the total correction, and compared with 17 eyes treated with the multizone software using the same parameters as in the low myopia group. RESULTS: Multizone treatment induced less initial hyperopic shift than monozone or multipass techniques, with significant differences at 15 days and 1 month. At 6 months after surgery 100% of low myopes and 88.24% of high myopes treated with the multizone software were within +/- 1.00 D of emmetropia as compared with 90.5% of the monozone eyes and 52.9% of the multipass patients. CONCLUSION: In low myopes this improvement seems to be related only to the increase in ablation diameter, but in high myopes we found a great improvement in the ablation profile and a shortening of the procedure as the likely factors of the better results obtained with multizone ablation.
Carones, F., R. Brancato, et al. (1996). "Evaluation of three different approaches to perform excimer laser photorefractive keratectomy for myopia." Ophthalmic Surg Lasers 27(5 Suppl): S458-65.
BACKGROUND AND OBJECTIVE: The aim of this study was to evaluate the results of myopic excimer laser photorefractive keratectomy (PRK) performed using three different ablation approaches. PATIENTS AND METHODS: Using the Apex excimer laser (Summit Technology, Inc., Waltham MA), we have treated 75 eyes. Twenty-five of them were treated by a single ablation zone (SA, 6.5 mm diameter) to correct myopia of -4.50 +/- 2.10 D (mean +/- SD); 25 eyes underwent PRK for the correction of myopia of -4.98 +/- 2.17 D using a multipass multizone technique (MP, 3 zones); and 25 eyes were corrected for myopia of -5.03 +/- 1.98 D using new software which enables the creation of three ablation zones in a single-pass fashion (MZ). RESULTS: Mean refractive error (+/-SD) at the first post-operative month was +1.34 +/- 1.00 D for SA, +1.78 +/- 1.49 D for MP, and +0.90 +/- 0.75 D for MZ. Eyes treated by MZ had significantly better uncorrected visual acuity than those treated by SA (P=0.04). Corneal topography revealed a central island in 14 eyes (56%) of those treated by SA and 2 eyes (8%) of those treated by MZ, but in no eyes treated by MP. Six months after treatment, mean refractive error was +0.28 +/- 0.75 D for SA, +0.36 +/- 0.92 D for MP, and - 0.07 +/- 0.77 D for MZ. CONCLUSION: MZ ablation induced less hyperopic shift at 1 month, thus leading to a faster visual recovery and better uncorrected visual acuity. MP and MZ ablations proved effective in preventing central island formation, thus inducing less visual disturbances than SA ablations. These results suggest that MZ ablation may be preferable to the other techniques in performing myopic PRK.
Kwitko, M. L., J. Gow, et al. (1996). "Excimer laser photorefractive keratectomy: one year follow-up." Ophthalmic Surg Lasers 27(5 Suppl): S454-7.
BACKGROUND AND OBJECTIVE: To confirm the effectiveness of the 193 nm excimer laser to correct low myopia (1.00 to 6.00 D), moderate myopia (6.00 to 10.00 D), and high myopia (10.00 D and above). PATIENTS AND METHODS: One hundred eighty-one eyes of 114 patients underwent excimer laser photorefractive keratectomy (PRK). The minimum follow-up was 12 months. RESULTS: After one year, 96% of the eyes in the low myopia group, 69% in the moderate myopia group and 29% in the high myopia group achieved uncorrected visual acuity of 20/40 or better with one treatment using a single application with a 5 mm optic zone. There were no significant major complications. CONCLUSION: PRK is a safe, effective and relatively accurate procedure to correct low to moderate myopia.
Quah, B. L., E. Y. Wong, et al. (1996). "Analysis of photorefractive keratectomy patients who have not had PRK in their second eye." Ophthalmic Surg Lasers 27(5 Suppl): S429-34.
BACKGROUND AND OBJECTIVE: Excimer laser photorefractive keratectomy (PRK) is performed at the Singapore National Eye Centre (SNEC) with a minimum period of 3 months between first and second eye treatment. During this period, iatrogenic anisometropia may occur, which can lead to significant visual disability. We analyzed the reasons why some patients delayed or did not receive PRK treatment to their second eye. The reasons for originally electing PRK, and the expectations these patients had, were also studied. PATIENTS AND METHODS: Between January 1992 and September 1993, 341 patients underwent PRK at SNEC. Of these, 86 (25.2%) did not receive PRK to their fellow eye within 1 year of follow-up and were recruited into the study. Data were collected retrospectively using a standardized questionnaire, and objective clinical data were obtained from the case records. Sixty-eight patients (79%) responded. RESULTS: Fifty-one patients (14.9%) had not undergone PRK at the conclusion of the study (mean follow-up = 31 months). Of these, 36 were due to dissatisfaction with the results of the procedure. Symptoms relating to hypermetropia (15 patients) and symptoms of glare and halos were the main reasons which discouraged patients from receiving PRK in their fellow eye. Seventeen of the 51 patients (33.3%) who did not have PRK performed in the second eye were overcorrected to hypermetropia, as opposed to 9 out of 255 patients (3.5%) who had PRK in the second eye (P < 0.001, chi-square test). Seventy-five percent of the patients who did not undergo PRK in the second eye expected postlaser unaided vision to be equal to prelaser best corrected vision; however, only 23% of these patients achieved this. CONCLUSION: Hypermetropia, glare and halos are significant causes of patient dissatisfaction after PRK. Patients who request PRK should be advised against harboring unrealistically high expectations for the procedure.
Helmy, S. A., A. Salah, et al. (1996). "Photorefractive keratectomy and laser in situ keratomileusis for myopia between 6.00 and 10.00 diopters." J Refract Surg 12(3): 417-21.
BACKGROUND: Excimer laser photorefractive keratectomy (PRK) can be effective in correcting myopia up to -6.00 diopters (D). Between -6.00 D and -10.00 D, the procedure is considered less effective and safe because it has been associated with dense scar formation and a high rate of regression. We compared photorefractive keratectomy (PRK) in this group of myopes with excimer laser keratomileusis in situ (LASIK). METHODS: Forty consecutive eyes with a manifest refraction between -6.00 and -10.00 D were treated with PRK using an ablation-zone diameter of 6 mm. Subsequently, 40 consecutive eyes were treated with LASIK under a hinged flap using an ablation-zone diameter of 5 mm. All procedures used a Summit OmniMed laser and were done by the same surgeon. RESULTS: Preoperatively, 24 eyes (60%) undergoing PRK had 20/20 spectacle-corrected visual acuity; 1 year postoperatively, 20 (50%) had 20/20 vision uncorrected. Preoperatively, 13 eyes (33%) undergoing LASIK had 20/20 spectacle-corrected visual acuity; 1 year postoperatively, 24 (60%) could see 20/20 uncorrected. Sixteen (39%) PRK eyes had a spherical equivalent refraction within +/-1.00 D at 1 year; 20 (60%) eyes undergoing LASIK had a refraction within +/-1.00 D at that point. None of the eyes treated with LASIK developed corneal haze, while after PRK, 36 eyes (90%) developed haze (23 eyes [57%] +2 to +3). CONCLUSION: LASIK under a hinged flap proved superior to PRK in treating myopia between -6.00 D and -10.00 D.
Patel, S. and J. Marshall (1996). "Corneal asphericity and its implications for photorefractive keratectomy: a mathematical model." J Refract Surg 12(3): 347-51.
BACKGROUND: Several clinical trials investigating myopic excimer laser photorefractive keratectomy (PRK) report an initial change in refraction from myopia to hyperopia, followed by a gradual regression toward emmetropia and occasionally to recurrent myopia. We examined the effect of corneal shape on refraction following PRK for myopia using a mathematical model. METHODS: We calculated the volume of corneal tissue removed by PRK for -3.00-diopter (D) and -6.00-D corrections with ablation diameters of 5 mm and 6 mm. For all the operating algorithms, the central region of the cornea was considered spherical. Mathematical models were developed based on calculations of the apical radius of the ablated cornea and the final refraction for a range of corneal asphericities. Baker's equation was used to model corneal asphericity. RESULTS: The smaller both the ablation size and desired correction, the smaller the effect of corneal asphericity on the refractive outcome. While corneal asphericity can influence the immediate refraction after PRK, the maximum effect is unlikely to be greater than +0.75 D. CONCLUSIONS: Corneal asphericity marginally affects the initial outcome of PRK. The effect will probably be offset by the healing response of the cornea.
Schallhorn, S. C., C. L. Blanton, et al. (1996). "Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel." Ophthalmology 103(1): 5-22.
PURPOSE: To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel. METHODS: Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare. RESULTS: At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure. CONCLUSIONS: Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.
Schipper, I. and P. Senn (1995). "Results of reshaping with the 193-nm excimer laser." Ger J Ophthalmol 4(3): 157-61.
We report herein our experience with reshaping following primary photorefractive keratectomy (PRK). Reshaping was performed on 7 of 116 myopic eyes (6 patients) 6-12 months subsequent to initial treatment. We carried out reshaping on 5 eyes (4 patients) for either undercorrection or regression. The mean preoperative refraction was -6.9 D, and at 1 year postsurgery it was -0.3 D. At 6 months following reshaping, the mean refraction was -0.15 D and the average uncorrected visual acuity (VA) was 20/25. In one patient, retreatment was performed 6 months after initial PRK due to marked regression and deterioration of VA. At 9 months subsequent to reshaping, the VA had improved to 20/25 with spherical correction of -1.0 D. In another patient, the best corrected VA deterioriated from 20/40 (-13.5 D) to 20/80, with hyperopia of +3.5 D being combined with marked scarring. At 6 months following phototherapeutic keratectomy (PTK), the VA had improved to 20/50, with spherical correction of +1.0 D. In conclusion, these observations demonstrate that reshaping is a satisfactory mode of treatment in certain indications.
Wang, W., B. Li, et al. (1995). "An empirical model of hyperopic shift with corticosteroid modulation and refractive power prediction after photorefractive keratectomy." J Refract Surg 11(3 Suppl): S314-8.
Data from a selected sample of 158 patients who received excimer laser photorefractive keratectomy (PRK) in our center and obtained a desirable refractive outcome at 6-months were analyzed retrospectively to establish an empirical model of refractive power after PRK. This model, generated by a computer-assisted regression program, is presented as a multivariate non-linear quadratic equation. Since the coefficients of each variable (attempted correction and postoperative days) are statistically significant, the estimated influence of the variables on the postoperative refraction from this regression model is reliable and consistent. Therefore, this model has been used to direct the use of corticosteroids for modulating post-PRK refraction. The predictability of this model has also been corroborated by separate data from 1-year follow up of PRK recipients. The recipients whose refraction at 6 months agree with the calculation from this model have obtained an excellent outcome; while those whose refractive outcome deviates from this model have gotten undesirable results.
Nagy, Z. Z., I. Suveges, et al. (1995). "Refractive results after photorefractive excimer laser treatment in mild myopic and in mild hyperopic eyes." Acta Chir Hung 35(3-4): 315-24.
Evaluation of 12-month results of photorefractive keratectomies (PRK) performed in low myopic (0 to -6.0 D) and low hyperopic (0 to +6.0 D) eyes. Myopic and hyperopic PRK treatments with the Aesculap Meditec MEL 60 ArF excimer laser. Prospective study, 30 eyes per group. The change in best corrected visual acuity (VA), refraction required, uncorrected VA and the postoperative haze were compared at the 12th postoperative month. The average preoperative correction in the low myopic eyes (Group I) was -4.65 +/- 1.24 D, which decreased to -0.17 +/- 0.56 D during the follow-up. In mild hyperopic eyes (Group II) the preoperative refraction was +3.9 +/- 0.93 D and decreased to +1.23 +/- 1.59 D post-PRK. Comparing the pre- and postoperative average best corrected VA values, there was no statistical change in either group. In the low myopic group all eyes had a 20/40 or better uncorrected VA, in hyperopic eyes 11 had a VA of 20/40 or better, four had a worse uncorrected VA. In Group I, 86.6% of the eyes were within +/-1.0 D of the intended refraction at 12 months postoperatively. In Group II, 46.7% of the eyes were within +/-1.0 D of final refraction. There were no intergroup differences in subjective complaints, reepithelization and average postoperative haze. Both methods are able to alter the refractive power of the cornea toward emmetropia. The predictability of the method was to be found higher in cases of mild myopia than in mild hyperopia. The upper limit of myopia is above -6.0 D, but in hyperopia, with the present technical facilities, good postoperative results can be obtained only as far as +4.25 D of preoperative refractive error.
Lin, D. T. (1994). "Corneal topographic analysis after excimer photorefractive keratectomy." Ophthalmology 101(8): 1432-9.
BACKGROUND: A 2-year experience with corneal topography after photorefractive keratectomy (PRK) is reported, specifically reviewing the correlation of surface regularity index versus best spectacle-corrected visual acuity as a function of various ablation patterns. Centration and stability issues also are discussed. METHODS: Excimer laser PRK for myopia was performed on 502 consecutive eyes. Corneal topographic analysis was performed at the 1-, 3-, 6-, and 12-month postoperative follow-up visits. In all patients, PRK was performed with an argon fluoride laser, and a topographic analysis was done. RESULTS: Topographic analysis at the first postoperative month was useful for determining decentration of the optical zone. The mean decentration from the pupillary center for all eyes was 0.34 mm. Four main patterns of ablation were noted by subtraction analysis. At the 1-month postoperative examination, a "uniform" ablation was present in 44% of eyes, "keyhole" ablations were present in 12% of eyes, "semicircular" ablations were present in 18% of eyes, and an unusual "central island" was present in the remaining 26% of eyes. However, on subsequent follow-up the central islands tended to resolve with time. At 3 months postoperatively, 18% of eyes in that group showed a central island, 8% showed a central island at 6 months, and only 2% of eyes showed a central island at the 12-month postoperative visit. Correlation of central island topography with visual acuity and progressive hyperopia are discussed. CONCLUSIONS: Corneal topography is essential for evaluating surface changes after excimer PRK. The surface regularity index is a good indicator of best spectacle-corrected visual acuity and is used to evaluate irregular astigmatism after PRK. Central island topographies are correlated with poor initial visual rehabilitation. Long-term stability issues are answered with continued topographic follow-up. Understanding corneal hydration changes between the central and peripheral cornea may help us understand the etiology of central islands.
Seiler, T., A. Holschbach, et al. (1994). "Complications of myopic photorefractive keratectomy with the excimer laser." Ophthalmology 101(1): 153-60.
BACKGROUND: Although many thousands of myopic eyes have been operated on by excimer laser photorefractive keratectomy (PRK), the safety of this procedure is still a concern. METHODS: The results and complications of PRK have been studied for up to 2 years in a prospective trial including 193 eyes in 146 patients. In addition, specific complications of PRK are described that occurred in patients outside the prospective study. RESULTS: Two eyes (1.2%) lost two lines of best-spectacle-corrected visual acuity 1 year after surgery, but at 2 years one of these eyes had regained baseline visual acuity. At 1 year, 12 eyes (7.1%) had lost more than two lines of visual acuity under glare conditions. Significant complications such as manifest scarring, overcorrection, undercorrection, and continued regression are dependent on attempted refraction. Eccentric ablations with resultant induced astigmatism are rare and the incidence is dependent on the experience of the surgeon. Progressive hyperopia did not occur. CONCLUSION: Except in corrections greater than 6 diopters, complications after PRK are rare. Assuming an appropriate patient selection, PRK may be considered a relatively safe procedure compared with other refractive procedures.
Goes, F. (1992). "Short term results with excimer laser-photo-refractive keratectomy." Bull Soc Belge Ophtalmol 245: 69-74.
The results at three months after photo-refractive keratectomy surgery (PRK) with the Meditec Mel 60 laser are discussed. A total of 86 eyes (18 hyperopes and 68 myopes) were followed. The predictability of +/- 1D in the myopia group of less than 6D was 86% and it was 68% in the myopia group of more than 6D. The predictability of +/- 2D was 96% in the group below 6D, and in the group of more than 6D it was 85%. In hyperopia, the mean refractive change was 2.7D and 44% of eyes were between +/- 1D at three months after Excimer laser surgery.