24-MONTH FOLLOW-UP OF EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA - REFRACTIVE AND VISUAL-ACUITY RESULTS

Purpose: To evaluate the 24-month refractive outcome of excimer laser photorefractive keratectomy (PRK) performed on normal, sighted myopic eyes; and to assess the evolution of postoperative refraction, the acc uracy of predicted correction, and the results in terms of uncorrected visual acuity. Methods: Photorefractive keratectomy was performed on 495 eyes, with a preoperative refraction ranging from -1.25 to -7.50 d iopters (D). Ablation zone diameters of 4.3 and 4.5 mm were used. All patients were treated with a standard topical steroid regimen postoper atively. Minimum follow-up time was 24 months. Results: Mean refractio n (spherical equivalent +/- standard deviation) at 24 months was -0.27 +/- 0.74 D, which was significantly (P < 0.01) different from the mea n at 12 months(0.01 +/- 0.78 D). There was also a significant (P = 0.0 1) difference between the 12- and 18-month (-0.15 +/- 0.82 D) mean ref ractions. But there was no significant difference between the means at 18 and 24 months postoperatively. Subgroup analysis at 24 months show ed that patients with low to moderate myopia (up to -3.90 D) had signi ficantly better refractive outcomes than those with higher myopia. Als o at 24 months, 91% of the eyes had an uncorrected visual acuity of at least 20/40, and 81.5% had an uncorrected visual acuity of at least 2 0/30. Correspondingly, 87.5% of the eyes were within 1.00 D of emmetro pia, and 71.7% were within 0.50 D. Only 0.4% lost one line of best-cor rected visual acuity, no eye lost two lines or more. Conclusions: Refr action after PRK is slow to stabilize, but appears to reach stability by 18 to 24 months after surgery. The refractive results are reasonabl y predictable and compare well with those achieved with radial keratot omy.