Effects of ablation diameter, depth, and edge contour on the outcome of excimer laser photorefractive keratectomy (abstract)

To investigate the effects of the ablation diameter, depth and edge contour on the outcome of excimer laser photorefractive keratectomy (PRK). Sixty patients were randomly allocated to 5.00 ram, 6.00 mm, or multizone treatment groups and underwent -6.00 diopters (D) corrections. A Summit OmniMed excimer laser (Summitt Technology, Inc., Waltham, Mass.) was used throughout. In eyes treated with 6.00 mm diameters the initial hyperopic shift was reduced, with significant differences at 1 and 4 weeks (p<0.01). At 6 and 12 months, the refractive changes were closer to the intended correction with 6.00 mm diameters. The predictability of PRK was improved with 6.00 mm zones with significant reduction in variance of the refractive changes, at all stages postoperatively (p<0.05 to p<0.001). Objective measurements of haze were significantly less than 1, 3, and 6 months with 6.00 mm ablations (p<0.05). There were no differences between the 5.00 mm and multizone groups. Computerized measurements of 'night' halo were significantly smaller in the 6.00 mm treatment group at 1 week and 1 month (p<0.05). At 12 months, 2 patients treated with 5.00 mm zones and 3 with multizones complained of severe night vision disturbances. No 6.00 mm eyes were similarly affected. Treatment with 6.00 mm spherical ablation diameters precipitated less initial overcorrection, improved predictability and was associated with a reduction in complications impairing postoperative visual performance. Creating a superficial blend zone with a multizone treatment had no effect on the outcome.