RESULTS OF EXCIMER-LASER RETREATMENT OF RESIDUAL MYOPIA AFTER PREVIOUS PHOTOREFRACTIVE KERATECTOMY

Background: Nine percent to 30% of all patients who undergo a single e xcimer laser photorefractive keratectomy (PRK) do not achieve an unaid ed visual acuity of 20/40 or better and may require optical correction to obtain adequate vision. Methods: The authors performed a retrospec tive analysis of the records of 164 patients who had undergone retreat ment with the excimer laser for residual myopia after a previous PRK. Mean follow-up was 35.5 +/- 15.2 weeks (range, 26-104 weeks). Results: The mean spherical equivalent (MSE) before retreatment was -2.59 +/- 1.36 diopter (D) (range, -0.50 to -7.75 D). The final MSE after reabla tion was -0.52 +/- 1.36 D (range, 2.50 to -5.50), Of the 164 patients, 107 (65.2%) obtained a final refraction within 1.00 D of emmetropia a nd 111 (67.3%) achieved an unaided visual acuity of 20/40 or better. O nly 10 patients (6.1%) lost more than one Snellen line of best-correct ed visual acuity. The final MSE result for the subgroup of patients wh o had a pre-retreatment myopia of between -0.50 and -1.90 D (-0.31 +/- 1.09 D) was significantly closer to emmetropia than that of the subgr oup with a residual myopia of -4.00 to -7.75 D (-1.62 +/- 1.94D). Conc lusions: Excimer laser retreatment may provide a relatively safe and p redictable method of correcting residual myopia after an earlier PRK w ith a 25% extra correction recommended for residual myopia.