Photoastigmatic refractive keratectomy in myopes

PURPOSE: Photoastigmatic refractive keratectomy (PARK) was studied in a mul ti-center clinical trial. The Nidek EC-5000 excimer laser was evaluated for its effect on refraction, visual acuity, and safety measures as part of a U.S. Food and Drug Administration (FDA) regulated study. METHODS: Eight U.S. centers enrolled adults with eyes having refractive ast igmatism up to 4.00 D and a myopic spherical equivalent refraction up to -8 .00 D. Results are reported for 749 eyes of 486 patients with at least 6 mo nths follow-up. The rectangular beam scanning Nidek EC-5000 used a 5.5-mm-d iameter treatment zone, a 7.0-mm-diameter peripheral blend zone, and a 40 H z pulse rate for surface treatment of myopic astigmatism. Nomogram correcti ons to machine settings were required to achieve the desired results. RESULTS: Preoperative average spherical equivalent refraction of -4.90 +/- 1.74 D was reduced to -0.02 +/- 0.79 D at 6 months. Refractive stability wa s established at 3 months. Over 62% of eyes were within +/-0.50 D of desire d correction at 6 months, with over 86% within +/-1.00 D. Uncorrected visua l acuity improved by an average of 10 Snellen lines; over 64% of eyes saw 2 0/20 or better uncorrected and over 93% saw 20/40 or better uncorrected at 6 and 12 months, PARK treatment effectively reduced astigmatism with little average axis error or magnitude error, Corneal haze and safety concerns we re minimal, CONCLUSIONS: Photoastigmatic refractive keratectomy using the Nidek EC-5000 excimer laser provided significant reduction of myopia and astigmatism, wi th minimal complications.