RESULTS OF PHOTOREFRACTIVE KERATECTOMY FOR LOW, MODERATE, AND HIGH MYOPIA

PURPOSE: To compare the predictability, safety, and stability of photo refractive keratectomy (PRK) in patient groups with low, moderate, and high myopia. The astigmatic component of these corrections was alsb e valuated. METHODS: In 110 patients, 110 consecutive eyes were operated with a VISX 20/20 excimer laser using standard settings and a 6 mm ab lation zone for PRK. The eyes were divided into three groups. In low m yopia group (N=52) the intended correction ranged from -1.50 to -6.00 D (mean -4.28 +/- 1.29 D), in the moderate myopia group (N=34) from -6 .10 to -8.00 D (mean -7.05 +/- 0.70 D), and in the high myopia group ( N=24) from -8.10 to -11.50 D (mean -9.40 +/- 1.13 D). Twenty-seven eye s had 0.75 D of preoperative myopic astigmatism. All patients were fol lowed for 12 months and 36% (N=40) were available for the 24-month fol low-up examination. RESULTS: At 12 months the spherical equivalent man ifest refraction was within 0.50 D of intended refraction in 58% (N=30 ) of eyes in the low myopia group, 50% (N=17) in the moderate myopia g roup, and 29% (N=7) in the high myopia group. Eighty-seven percent (N= 45) in low, 79% (N=27) in moderate, and 67% (N=16) in the high myopia group were within 1.00 D of intended refraction. At 12 months, 88% (N= 46) of the eyes with low myopia, 68% (N=23) with moderate myopia, and 68% (N=16) with high myopia achieved uncorrected visual acuity of 20/4 0 or better, while 6% (N=16) of the eyes lost and 4% (N=4) gained two or more Lines of Snellen visual acuity. Uncorrected visual acuity of 2 0/20 or better at 12 months was achieved by 58% (N=30) of low myopes, 26% (N=9) of moderate myopes, and 33% (N=8) of high myopes; 20/25 or b etter by 71% (N=37) of low myopes, 39% (N=13) of moderate myopes, and 42% (N=10) of high myopes. Overcorrection (>0.25 D) was detected at 12 months in 31% (N=16) with low, 38% (N=13) with moderate, and 67% (N=1 6) with high baseline myopia, with statistically significant differenc es between the low and high myopia groups. CONCLUSION: In all groups, the safety of PRK was satisfactory, without major complications; in th e high myopia group where corrections exceeded 8.0 D (mean -9.40 +/- 1 .13 D) the procedure was only slightly more unpredictable than in low and moderate myopia at 1 year.