Factors associated with changes in posterior corneal surface following photorefractive keratectomy

Purpose: To identify factors associated with changes in the posterior cornea curvature following laser refractive surgery. Materials and methods: This retrospective study included myopic astigmatic eyes that underwent PRK between January 2013 and December 2013 at Care-Vision Laser Centers, Tel-Aviv, Israel. The average posterior K was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgical induced change in average posterior k and preoperative parameters such as central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci index (BCV), ablation depth, percent tissue altered (PTA), and residual stroma bed (RSB) were analyzed. Results: A total of 280 eyes with a mean age of 24.9 ± 6.1 years (range, 18–47 years were included in this study. The mean PTA was 14.8 ± 6.0%. A greater change in posterior K was found in females (p = 0.01), smaller treatment zones of 6.0 mm (p = 0.02) and PTA > 20% (p < 0.001). A lower CCT (r = − 0.24, p < 0.001), higher myopia (r = − 0.34, p < 0.001), higher astigmatism (r = − 0.17, p < 0.001), higher total BCV (r = 0.13, p = 0.03), lower back BCV (r = − 0.12, p = 0.05), higher front BCV (r = 0.16, p = 0.01), higher posterior I-S ratio (r = 0.16, p = 0.01), and a lower RSB (r = − 0.42, p < 0.001) were all significantly correlated with percentage of change in mean posterior K. In ranked stepwise multiple regression analysis, 26.2% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were PTA (p < 0.001), CCT (p = 0.001), and posterior I-S ratio (p = 0.001). PTA alone accounted for 15% of the variance in posterior K changes in multivariate analysis. Conclusions: Understanding of factors affecting a change in posterior cornea after refractive surgery may have an important practical value for the prevention of iatrogenic keratectasia. Preoperative CCT, posterior I-S ratio, and PTA were significantly associated with changes in posterior K after PRK. PTA was the strongest predictor of posterior corneal changes (p < 0.001).[Figure not available: see fulltext.]