REFRACTIVE OUTCOME AND CORNEAL TOPOGRAPHIC STUDIES AFTER PHOTOREFRACTIVE KERATECTOMY WITH DIFFERENT-SIZED ABLATION ZONES

Background: Discrepancies may still occur between planned and actual r efractive correction in eyes undergoing photorefractive keratectomy (P RK). The authors have evaluated the use of an enlarged ablation zone. Method: A computerized corneal analysis system has been used to compar e the changes of the anterior surface of the cornea and the refractive changes before and 1, 6, and 12 months after PRK in 113 patients (119 eyes) treated with an excimer laser. The patients were divided into t wo groups: those treated with a mask with a 5-mm window (59 eyes), and those with a new mask with different window openings according to the degree of refraction at the corneal apex, starting from 5 mm in diame ter for treatments less than 6.5 diopters (D) and from 7 mm in diamete r for higher treatments (60 eyes). In the first group, treatment range d from -2.5 to -16 D (mean +/- standard deviation, -8.5 +/- 3.24 D); i n the second group, it ranged from -1 to -14 D (-7.8 +/- 3.06 D). Trea tments were evaluated with a chi-square test. Results: In the first gr oup of eyes, 46% were within +/- 1 D at 1 month, 37% at 6 months, and 39% at 12 months. In the second group of eyes, 73% were within +/- 1 D at 1 month, 60% at 6 months, and 58% at 12 months. The comparison bet ween these data and corneal topographic changes shows that both are mo re stable and predictable with the new mask compared with the 5-mm mas k (P = 0.002, 0.02, 0.04, at 1, 6, and 12 months, respectively). Concl usions: The use of larger ablation zones improves the predictability a nd stability of refractive changes.