The experience with excimer laser correction of

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1 Prospective Study of Photorefractive Keratectomy for Hyperopia Using an Axicon Lens and Erodible Mask Weldon W. Haw, MD; Edward E. Manche, MD ABSTRACT PURPOSE: To evaluate prospectively the longterm 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 ± 0.82 D (range, to 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 ± 0.87 D (range, to 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 spectaclecorrected 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 From the Stanford University School of Medicine, Department of Ophthalmology, Stanford, CA. The authors have no proprietary interest in the materials presented herein. Correspondence: Edward E. Manche, MD, Stanford University School of Medicine, Department of Ophthalmology, 300 Pasteur Drive, Suite A175, Stanford, CA Tel: ; Fax: Received: May 24, 2000 Accepted: September 19, 2000 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 spectaclecorrected visual acuity took approximately 6 months. [J Refract Surg 2000;16: ] The experience with excimer laser correction of myopia has been widely studied. By comparison, the use of the excimer laser for the correction of hyperopia has been less developed. Photorefractive keratectomy (PRK) has been studied in the treatment of low to moderate levels of hyperopia. 1-9 This involves a peripheral annular ablation around the central optical zone which steepens the central cornea. 10 Early clinical trials used smaller ablation zones that required high levels of accuracy. These early studies resulted in unacceptable levels of decentration, regression, and loss of best spectacle-corrected visual acuity (Anschutz T. Hyperopic PRK. Ophthalmology Times 1994; 8:21). 9 Currently, larger treatment zones consisting of a 5.5 to 6.0-mm ablation zone in conjunction with a 9.0-mm ablation zone diameter are being employed by most laser manufacturers to treat hyperopia. 11 Larger zones have resulted in improved clinical results following PRK for hyperopia. 5-6 Technology has resulted in the development of an erodible disc and the axicon lens. The erodible disc delivery system has the theoretical advantage of transferring any three-dimensional shape onto the corneal surface by photoablation. 12 The axicon lens is a quartz lens that is used to gradually smooth a peripheral blend zone. 3 We evaluated prospectively the long-term safety, efficacy, contrast sensitivity function, and visual performance of patients undergoing PRK for hyperopia using erodible disc technology and an axicon quartz lens. 724 Journal of Refractive Surgery Volume 16 November/December 2000

2 PATIENTS AND METHODS In this prospective, noncomparative case series, we enrolled 18 eyes of 9 patients at a single center (Stanford Eye Laser Center, Stanford, CA). Appropriate Institutional Review Board approval was obtained prior to beginning the study. All patients completed an informed consent. Patients were eligible for enrollment if they demonstrated to diopters (D) of spherical hyperopia with less than 1.00 D of astigmatism. Other inclusion criteria included an age of at least 18 years, preoperative best spectacle-corrected visual acuity of 20/25 or better, and a stable refractive error of ±1.00 D for 1 year. Exclusion criteria included patients with autoimmune diseases or vasculopathies, clinically significant ocular disease, systemic diseases or drugs affecting cornea healing, eg, corticosteroids, >1.00 D discrepancy between preoperative manifest and cycloplegic refraction, intraocular pressure >21.0 mmhg, previous ocular surgery, or patients enrolled in other studies. Preoperative serial corneal topography was performed until no evidence of warpage induced by contact lens was observed. Patients meeting the above criteria underwent an extensive preoperative medical and ocular history and examination. Distance uncorrected visual acuity (UCVA), manifest and cycloplegic refraction, slitlamp microscopy, Goldmann tonometry, corneal topography, and dilated fundus examination were performed on preoperative examination. Visual acuity was measured using a backlighted Lighthouse Distance Visual Acuity Test (2nd edition, Lighthouse Low Vision Products, Long Island, NY) which uses a modified ETDRS chart with Sloan letters. Visual acuity is reported as Snellen distance equivalent. Best spectacle-corrected distance visual acuity under scotopic (21 lux), photopic (324 lux), and glare conditions was also measured during the preoperative examination. Glare conditions were simulated with a handheld brightness acuity test meter (Mentor, Norwell, MA) at the maximum setting. Best spectacle-corrected and uncorrected near visual acuity were measured using the Lighthouse Near Visual Acuity Test (2nd edition, Lighthouse Low Vision Products, Long Island, NY). Contrast sensitivity function was measured under scotopic (21 lux) and photopic (324 lux) conditions with the best spectacle correction in place. Contrast sensitivity was measured using a backlighted CSV-1000E (Vector Vision, Dayton, OH) which employs a vertical grating system at four standard spatial frequencies (3.0, 6.0, 12.0, and 18.0 cycles/degree). For each spatial frequency, the grating becomes progressively more difficult to discern. Each grating corresponds to a contrast sensitivity value (log units) provided by Vector Vision (Dayton, OH). After instillation of diclofenac sodium 0.1% (Voltaren, CIBA Vision Ophthalmics, Duluth, GA), ofloxacin 0.3% (Ocuflox, Allergan, Irvine, CA), and proparacaine hydrochloride 0.5% (Ophthetic, Allergan, Irvine, CA), the corneal epithelium overlying the 9.5-mm ablation zone was removed with a blunt PRK spatula. The surgeon focused the two helium-neon aiming beams on the corneal surface over the center of the pupil and completed the photoablation through the erodible polymethylmethacrylate (PMMA) disc inserted into the laser rail. All procedures were performed by a single surgeon (EEM) using the Summit Apex Plus excimer laser (Summit Technology Inc., Waltham, MA). The operating system employed standard settings including an energy fluence of 180 mj/cm 2 with a repetition rate of 10 Hz. Following the hyperopic correction with the erodible disc, a nondisposable quartz axicon lens was used to smooth the peripheral blend zone between the treated and nontreated cornea. The axicon lens delivers energy in an annular pattern with its highest energy at the inner rim and progressively less energy delivery to the outer rim. This results in a smooth blend zone from 6.5 mm to 9.4 mm. The number of pulses is selected by the desired depth of ablation achieved by the peripheral ablation obtained from the erodible disc. This is a predetermined value established by the manufacturer. Following the procedure, the stroma was irrigated with chilled balanced salt solution and a bandage contact lens was placed until re-epithelialization was complete. Patients were begun on ofloxacin 0.3% qid until the epithelium was healed and fluorometholone 0.1% (FML, Allergan, Irvine, CA) qid for 1 month, then bid for 1 month. Patients were evaluated prospectively at 1, 3, 6, 9, 12, 18, and 24 months. Primary outcome measurements included distance and near uncorrected visual acuity, refraction, best spectacle-corrected near visual acuity, and best spectacle-corrected distance visual acuity tested under scotopic (21 lux), photopic (324 lux), and glare conditions. Patients were also examined for contrast sensitivity at 3.0, 6.0, 12.0, and 18.0 cycles/degree under both scotopic (21 lux) and photopic (324 lux) conditions. Corneal haze was graded on a scale of 0 to 5 at the slit lamp by a single observer (EEM). SPSS Graduate Pack for Windows V6.1.3 (SPSS Inc, Chicago, IL) was used to determine statistical Journal of Refractive Surgery Volume 16 November/December

3 Baseline Table 1 Mean Refractive Outcome for 12 Eyes After PRK for Hyperopia Months After PRK for Hyperopia Sphere (D) +2.14± ± ± ± ± ± ± ±0.88 Cylinder (D) +0.25± ± ± ± ± ± ± ±0.35 Spherical equivalent refraction (D) +2.26± ± ± ± ± ± ± ±0.87 No. of eyes Table 2 Distance Uncorrected Visual Acuity in 12 Eyes After PRK for Hyperopia Months After PRK for Hyperopia Percent of eyes 20/20 or better Percent of eyes 20/40 or better Table 3 Mean Contrast Sensitivity for Each Spatial Frequency (log units) Under Scotopic Conditions for 12 Eyes After PRK for Hyperopia Spatial Frequency Baseline Months After PRK for Hyperopia (cycles/degree) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.26 Table 4 Mean Contrast Sensitivity for Each Spatial Frequency (log units) Under Photopic Conditions for 12 Eyes After PRK for Hyperopia Spatial Frequency Baseline Months After PRK for Hyperopia (cycles/degree) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.18 significance using the paired t-test. Differences were considered statistically significant when P<.05. RESULTS Figures 1-6 present standardized graphs that depict the results in this series, as recommended by Waring. 13 Mean preoperative sphere was ± 0.83 D (range, to D), mean preoperative cylinder was ± 0.27 D (range, 0 to D), and the mean preoperative spherical equivalent refraction was ± 0.82 D (range, to D). The mean age of the cohort was 53.5 ± 8.6 years of age. Twelve eyes (67%) were from females and 6 eyes (33%) were from males. Ninety-four percent to 100% 726 Journal of Refractive Surgery Volume 16 November/December 2000

4 Figure 1. Attempted vs. achieved refractive correction in 12 eyes at 24 months after PRK for hyperopia. Dashed line is ±1.00 D. Figure 2. Mean change in mean spherical equivalent refraction in 12 eyes after PRK for hyperopia. Error bars indicate 95% confidence interval. Figure 3. Change in best spectacle-corrected visual acuity (Snellen lines) in 12 eyes under scotopic, photopic, and glare conditions at 24 months after PRK for hyperopia. Figure 4. Defocus equivalent refraction in 12 eyes after PRK for hyperopia at 24 months. Figure 5. Postoperative spherical equivalent refraction in 12 eyes after PRK for hyperopia at 24 months. Figure 6. Uncorrected visual acuity (percent of 12 eyes) before and after PRK for hyperopia at 24 months. Journal of Refractive Surgery Volume 16 November/December

5 of eyes were available at all follow-up intervals (Table 1); 100% of the 18 eyes were examined at the 2-year follow-up interval. Refraction results are summarized in Table 1: 114.5% of the sphere was corrected to a mean residual of ± 0.88 D (range, to D) at the 24-month follow-up interval; 98.2% of the mean preoperative spherical equivalent refraction was corrected to ± 0.87 D (range, to D) during this same follow-up. At 24 months, 12 eyes (67%) were within ±0.50 D of attempted correction and 15 eyes (83%) were within ±1.00 D of attempted correction. All eyes were within ±2.00 D of attempted correction (Fig 1). A mean hyperopic regression of D occurred between 1 and 6 months following PRK for hyperopia. Stability within ±0.50 D was achieved after 6 months (Fig 2). Two eyes (11%) of the same patient underwent almost complete regression of refractive effect between 1 and 24 months. The majority of the regression in these eyes occurred in the first 9 postoperative months. These eyes accounted for 2 of 3 eyes with a predictability of less than ±1.00 D of attempted correction at the last follow-up interval. Table 2 summarizes the distance uncorrected visual acuity (UCVA) results for each postoperative interval. At 24 months, 12 eyes (67%) had an UCVA of 20/20 or better and all 18 eyes (100%) demonstrated an UCVA of 20/40 or better following the hyperopic PRK procedure. At 1 month, 11 eyes (65%) demonstrated a near uncorrected visual acuity of 20/25 or better and 16 eyes (94%) demonstrated a near UCVA of 20/40 or better. By 24 months, only 2 eyes (11%) demonstrated a near UCVA of 20/25 or better and 7 eyes (39%) demonstrated a near UCVA of 20/40 or better. Tables 3 and 4 summarize the mean contrast sensitivity (log units) under scotopic and photopic illuminance conditions for each postoperative interval. There was no statistically significant (P>.05) decrease in mean contrast sensitivity in any of the measured postoperative time intervals. One month following the hyperopic PRK procedure, 4 eyes (24%) lost 2 or more lines of best spectacle-corrected visual acuity (BSCVA) under scotopic conditions. A similar trend was demonstrated under photopic conditions where 5 eyes (29%) lost 2 or more lines and under glare conditions where 5 eyes (29%) lost 2 or more lines of BSCVA. There was continued improvement in BSCVA under scotopic, photopic, and glare conditions throughout the postoperative period. At 3 months, 2 eyes (12%) lost 2 or more lines under scotopic conditions, 0 eyes (0%) under photopic conditions, and 2 eyes (12%) Figure 7. Characteristic mid-peripheral ring of corneal haze 24 months after PRK for hyperopia. under glare conditions. At 24 months, no eyes lost 2 or more lines of best spectacle-corrected visual acuity under scotopic (21 lux) or photopic (324 lux) conditions (Fig 3). One eye (5.5%) lost 2 or more lines of best spectacle-corrected visual acuity under glare conditions. Anterior stromal haze was noted in 4 eyes (24%) at 1 month, 11 eyes (65%) at 6 months, and 12 eyes (71%) at 12 months. By 24 months, 14 eyes (78%) demonstrated grade 1 to 3 anterior stromal haze. The characteristic corneal haze was a peripheral complete or incomplete ring of haze with central sparing. (Fig 7). Notably, eyes with haze did not experience a decrease in measured contrast sensitivity nor best spectacle-corrected visual acuity under glare, scotopic, or photopic conditions. There were no intraoperative complications, decentrations, infectious keratitis, or delayed re-epithelialization or corticosteroid induced elevations in intraocular pressure. DISCUSSION Previous reports on the correction of hyperopia have demonstrated that PRK may effectively reduce hyperopia. Results vary depending on the magnitude of preoperative correction and the duration of follow-up. Overall, 17% to 98% of eyes are within ±1.00 D of attempted correction and 8% to 97% have an UCVA of 20/40 or better at the last follow-up examination. 1-7,9,14 Although myopia and compound myopic astigmatism have been treated with excimer laser refractive surgery, hyperopic corrections demonstrate unique challenges. Hyperopic corrections result in more significant initial overcorrection (myopic shift) and longer duration to stability. 3 In our study, the initial overcorrection of the mean spherical equivalent 728 Journal of Refractive Surgery Volume 16 November/December 2000

6 Figure 8. Corneal topography (EyeSys) of an eye 3 months after PRK for D of hyperopia shows well-centered corneal steepening. Figure 9. Corneal topography (EyeSys) of an eye 3 months after PRK for x 90 shows an exaggerated transition zone. Note the corneal steepening as demonstrated by the warmer colors on the videokeratograph. refraction was almost D at 1 month with hyperopic regression to emmetropia occurring between 18 and 24 months (Table 1). However, most of the hyperopic regression (+0.71 D) occurred within the first 6 months with stability within ±0.50 D occurring after 6 months. The improvement in near uncorrected visual acuity was the most significant early benefit following hyperopic PRK for presbyopic patients. The deterioration of near UCVA and improvement in distance UCVA during the postoperative period paralleled the hyperopic regression toward emmetropia. The slower recovery of best spectacle-corrected visual acuity (compared to PRK for myopia) following PRK for hyperopia has been proposed. 5 We measured BSCVA under controlled environmental circumstances scotopic (21 lux), photopic (324 lux), and glare conditions. Under all these conditions, there was an initial loss of BSCVA of 2 or more lines in 24% to 29% of eyes at the 1-month follow-up. However, there was progressive improvement in BSCVA under all illuminance conditions throughout the postoperative period. By 24 months, 0% of eyes had lost 2 or more lines of BSCVA under scotopic and photopic conditions and 5.5% of eyes lost 2 or more lines under glare conditions. Because the visual axis receives no photoablation during hyperopic corrections, one would expect a more rapid recovery as compared to myopic PRK. However, the significant early loss of BSCVA following hyperopic PRK may result from corneal irregularity resulting from abrupt changes in the transition from the ablated to unablated zone. 3,5 In addition, since a small ablation zone may occur following hyperopic PRK, small decentrations may be unforgiving and may also result in significant loss of best Journal of Refractive Surgery Volume 16 November/December

7 spectacle-corrected visual acuity. Under both conditions, continued epithelial and stromal healing may make this transition zone less pronounced over time, resulting in recovery of BSCVA. In our study, there were no visually significant decentrations. Figure 8 demonstrates typical, well-centered corneal steepening on corneal topography 3 months following hyperopic PRK for D. For larger magnitudes of hyperopic correction, the transition zone may be exaggerated. Figure 9 shows the corneal topography of an eye 3 months following hyperopic PRK for a baseline refraction of x 90. Our study demonstrated a significant tendency toward the development of corneal haze. The haze was later onset and characteristically resulted in a mid-peripheral ring (with sparing of the optical axis). The location of haze corresponded to where the depth of ablation was greatest. Unlike central corneal haze following myopic PRK which can result in symptoms of glare, halos, loss of best spectaclecorrected visual acuity and contrast sensitivity, we did not observe any effect of the mid-peripheral haze on visual performance or loss of best spectaclecorrected visual acuity. In our prospective long-term study, we described the long-term safety, efficacy, and visual performance following PRK for low to moderate levels of hyperopia. Continued improvements in the hyperopic ablation profile, hyperopic LASIK, and perhaps newer treatment modalities such as laser thermal keratoplasty, conductive keratoplasty, and hyperopic phakic intraocular lenses are expected to expand the indications and continue to improve the results of hyperopic corrections. REFERENCES 1. Jackson WB, Casson E, Hodge WG, Mintsioulis G, Agapitos PJ. Laser vision correction for low hyperopia. Ophthalmology 1998;105: Vinciguerra P, Epstein D, Radice P, Azzolini M. Long-term results of photorefractive keratectomy for hyperopia and hyperopic astigmatism. J Refract Surg 1998;14(suppl): S183-S Carones F, Brancato R, Morico A, Vigo L, Venturi E, Gobbi PG. Photorefractive keratectomy for hyperopia using an erodible disc and axicon lens: 2 year results. J Refract Surg 1998;14: Pietila J, Makinen P, Pajari S, Uusitalo H. Excimer laser photorefractive keratectomy for hyperopia. J Refract Surg 1997;13: Dausch D, Smecka Z, Klein R, Schroder E, Kirchner S. Excimer laser photorefractive keratectomy for hyperopia. J Cataract Refract Surg 1997;23: Jackson WB, Mintsioulis G, Agapitos PJ, Casson EJ. Excimer laser photorefractive keratectomy for low hyperopia: safety and efficacy. J Cataract Refract Surg 1997;23: Sener B, Ozdamar A, Aras C, Yanyali A. Photorefractive keratectomy for hyperopia and aphakia with a scanning spot excimer laser. J Refract Surg 1997;13: Vinciguerra P, Epstein D, Azzolini M, Radice P, Sborgia M. Algorithm to correct hyperopic astigmatism with the Nidek EC-5000 excimer laser. J Refract Surg 1999;15(suppl): S186-S Dausch D, Klein R, Schroder E. Excimer laser photorefractive keratectomy for hyperopia. Refract Corneal Surg 1993;9: L'Esperance FA Jr, Warner JW, Telfair WB, Yoder PR Jr, Martin CA. Excimer laser instrumentation and technique for human corneal surgery. Arch Ophthalmol 1989;107: Anschutz T, Pieger S. Evaluation of hyperopic photoablation profiles. J Refract Surg 1998;14(suppl):S192-S Maloney RK, Friedman M, Harmon T, Hayward M, Hagen K, Gailitis RP, Waring GO III. A prototype erodible mask delivery system for the excimer laser. Ophthalmology 1993;100: Waring GO III. Standard graphs for reporting refractive surgery. J Refract Surg 2000;16: O'Brart D, Stephenson CG, Baldwin H, Ilari L, Marshall J. Hyperopic photorefractive keratectomy with the erodible mask and Axicon system: Two year follow-up. J Cataract Refract Surg 2000;26: Journal of Refractive Surgery Volume 16 November/December 2000