To determine risk factors of regression and undercorrection following photorefractive keratectomy in myopia or myopic astigmatism.

A case-control study was designed in which eyes with an indication for re-treatment were defined as cases; controls were chosen from the same cohort of operated eyes which had complete post-operative follow up data beyond 9 months and did not need re-treatment. The cohort included patients who had undergone photorefractive keratectomy by the Tissue-Saving ablation profile of Technolas 217z100 excimer laser (Bausch & Lomb, Rochester, NY, USA). Mitomycin C had been used in all of the primary procedures.

We had 70 case eyes and 158 control eyes, and they were comparable in terms of age, sex and follow-up time (P values: 0.58, 1.00 and 0.89, respectively). Pre-operative spherical equivalent of more than -5.00 diopter (D), intended optical zone diameter of less than 6.00 mm and ocular fixation instability during laser ablation were associated with retreatment indications (all P values<0.001). These factors maintained their significance in the multiple logistic regression model with odd ratios of 6.12, 6.71 and 7.89, respectively.

Higher refractive correction (>-5.00 D), smaller optical zones (<6.00 mm) and unstable fixation during laser ablation of photorefractive keratectomy for myopia and myopic astigmatism were found to be strong predictors of undercorrection and regression.