Corneal topographic analysis of photorefractive keratectomy in 175 myopic eyes.

Videokeratography is a useful method for postoperative evaluation of photorefractive keratectomy (PRK). The aim of this study was to evaluate the percentage of decentration, the relationship between decentration relative to the corneal apex, postoperative astigmatism, and the relationship between decentration and best corrected Snellen visual acuity. Using the TMS-1 videokeratoscope we analyzed the corneal topography of 175 myopic eyes treated with PRKs ranging between -1.30 D and -15.90 D, performed using the Summit UV200 193-nanometer excimer laser, before and at least 6 months after the procedure. Concerning centration, 122 eyes (75%) were centered within 0.5 mm and 53 eyes (30.3%) were decentered more than 0.5 mm, with nine eyes (5.1%) being decentered more than 1 mm. There was a correlation between best spectacle corrected visual acuity and the amount of decentration. The higher attempted corrections showed greater amounts of decentration. Postoperative induced astigmatism was greater in the group with the highest decentration (1.81 +/- 2.64 D) than in the one with lower decentration (0.09 +/- 0.50 D). The most severe complication induced by a decentered PRK is an increase of postoperative astigmatism.