THE EFFECTS OF ABLATION DIAMETER ON THE OUTCOME EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY - A PROSPECTIVE, RANDOMIZED, DOUBLE-BLIND-STUDY

Objective: To determine the effects of the ablation diameter on the ou tcome of excimer laser photorefractive keratectomy. Design: Eighty pat ients 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) or a -6. 00-D correction based on their preoperative refraction. A Summit Omnim ed excimer laser was used throughout the study. Results: In eyes treat ed with a 6.00-mm-diameter ablation, the initial hyperopic shift was r educed, with significant differences at 1 week with -3.00-D correction s 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 kerat ectomy 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 sho wed 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 sign ificantly 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 sev ere regression of the correction, with marked corneal haze and a reduc tion of 3 or more lines of best corrected Snellen visual acuity at 6 m onths. No eyes treated with 6.00-mm zones were similarly affected. Com puterized measurements of ''night'' halo were significantly lower in t he 6.00-mm treatment groups at 1 week and at 1 and 6 months in the eye s with -3.00-D corrections and at 1 week and at 1 month in the eyes wi th -6.00-D corrections (P<.05). At 6 months, seven patients treated wi th 5.OO-mm zones complained of severe disturbances of night night visi on. No eyes in the 6.00-mm group were similarly affected. Conclusions: Treatment with 6.00-mm ablation diameters precipitated less initial o vercorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impa iring postoperative visual performance.