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April 1995

The Effects of Ablation Diameter on the Outcome of Excimer Laser Photorefractive KeratectomyA Prospective, Randomized, Double-Blind Study

Author Affiliations

From the Department of Ophthalmology, St Thomas' Hospital, London, England (Drs O'Brart, Corbett, Lohmann, Kerr Muir, and Marshall), and the University Eye Clinic, Regensburg, Germany (Dr Lohmann). Dr O'Brart holds a research fellowship sponsored by the Iris Fund for Prevention of Blindness, Dr Corbett holds the William's Fellowship for Medical and Scientific Research of the University of London, and Dr Marshall is a consultant for Summit Technology, Boston, Mass.

Arch Ophthalmol. 1995;113(4):438-443. doi:10.1001/archopht.1995.01100040054026

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.