The Effects of Ablation Diameter on the Outcome of Excimer Laser Photorefractive Keratectomy

Abstract

Objective: To determine the effects of the ablation diameter on the outcome of excimer laser photorefractive keratectomy. Design: Eighty patients were randomized to either a 5.00-mm or a 6.00-mm treatment group and within these groups underwent either a −3.00-diopter (D) ora −6.00-D correction based on their preoperative refraction. A Summit Omnimed excimer laser was used throughout the study. Results: In eyes treated with a 6.00-mm-diameter ablation, the initial hyperopic shift was reduced, with significant differences at 1 week with −3.00-D corrections and at 1 and 4 weeks with −6.00-D corrections (P<.01). At 6 months, the refractive changes were greater and closer to that intended with 6.00-mm-diameter ablations. The predictability of photorefractive keratectomy was significantly improved with 6.00-mm zones, with a reduction in variance of the refractive changes at all stages postoperatively (P<.05 to P<.001). With −3.00-D corrections, objective measurements showed significantly less anterior stromal haze in eyes treated with 6.00-mm zones at 6 months (P<.05). With −6.00-D corrections, haze was significantly reduced at 1, 3, and 6 months in the eyes treated with 6.00-mm zones (P<.05). Five eyes treated with 5.00-mm zones experienced severe regression of the correction, with marked corneal haze and a reduction of 3 or more lines of best corrected Snellen visual acuity at 6 months. No eyes treated with 6.00-mm zones were similarly affected. Computerized measurements of "night" halo were significantly lower in the 6.00-mm treatment groups at 1 week and at 1 and 6 months in the eyes with −3.00-D corrections and at 1 week and at 1 month in the eyes with −6.00-D corrections (P<.05). At 6 months, seven patients treated with 5.00-mm zones complained of severe disturbances of night vision. No eyes in the 6.00-mm group were similarly affected. Conclusions: Treatment with 6.00-mm ablation diameters precipitated less initial overcorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impairing postoperative visual performance.