Results of photorefractive keratectomy for low, moderate, and high myopia.

Abstract

To compare the predictability, safety, and stability of photorefractive keratectomy (PRK) in patient groups with low, moderate, and high myopia. The astigmatic component of these corrections was also evaluated. In 110 patients, 110 consecutive eyes were operated with a VISX 20/20 excimer laser using standard settings and a 6 mm ablation zone for PRK. The eyes were divided into three groups. In low myopia 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 eyes had 0.75 D of preoperative myopic astigmatism. All patients were followed for 12 months and 36% (N = 40) were available for the 24-month follow-up examination. At 12 months the spherical equivalent manifest 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 group, 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 20/40 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 20/20 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 better 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 = 16) with high baseline myopia, with statistically significant differences between the low and high myopia groups. In all groups, the safety of PRK was satisfactory, without major complications; in the 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.