Photorefractive keratectomy for compound myopic astigmatism

PURPOSE: To evaluate the safety and efficacy of photorefractive keratectomy for the treatment of primary compound myopic astigmatism. METHODS: Ln a prospective study, 93 eyes from 56 patients with a mean spherical equivalent of -4.98 +/- 1.80 diopters (range, -1.75 to -8.5) underwent photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser using erodible mask technology and were followed for 2 years. Primary outcome measures included an assessment of astigmatic correction through meter analysis, manifest refraction, uncorrected visual acuity, corneal clarity, and the presence of adverse symptoms. RESULTS: Eighty-five eyes (91.4%) were available for analysis at 6 months. Mean spherical equivalent refraction was reduced 85% (mean, -0.75 +/- 0.85 diopter) and the target-induced astigmatism was reduced 70% (mean, 0.98 +/- 1.88 diopters). Forty-eight eyes (56%) had an uncorrected visual acuity of 20/20 or greater, whereas 70 eyes (82%) had an uncorrected visual acuity of 20/40 or greater. Twenty-four eyes (26%) required re-treatment because of undercorrection of the spherical equivalent and astigmatic components after the 6-month follow-up. Fifty-nine of the remaining eyes were available at the 24-month visit. Mean spherical equivalent refraction was reduced to -0.39 +/- 0.12 diopter (91.8%). The target-induced astigmatism was reduced 64% from 1.74 diopters. Forty-one eyes (81.3%) were within +/-1.0 diopter of attempted spherical equivalent correction. Stability within a spherical equivalent of +/-0.5 diopter occurred after the first postop erative month. Fifty-six eyes (94.9%) had an uncorrected visual acuity of 20/40 or greater, whereas 34 eyes (57.6%) demonstrated an uncorrected visual acuity of 20/20 or greater. One eye (1.7%) lost 2 or more lines of best spectacle-corrected visual acuity. CONCLUSION: Photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser is a safe and effective method of reducing compound myopic astigmatism. However, higher re-treatment rates may result from significant undercorrections because of current laser algorithms and variability in the mean angle of error. (C) 2000 by Elsevier Science Inc. All rights reserved.