Clinical analysis of functional optical zone after transepithelial photorefractive keratectomy in patients with different degrees of myopic astigmatism

Background To evaluate the effects of preoperative myopic astigmatism and anterior corneal surface curvature on the functional optical ZONE (FOZ) after transepithelial photorefractive keratectomy(transPRK). Methods This retrospective study was conducted on 78patients(130 eyes) with myopia and myopic astigmatism who underwent transPRK and they were grouped according to myopic astigmatism: control group(cylinder 0D ), moderate astigmatism group (-0.50 to -2.0D),and high astigmatism group(>-2.00 to -6.00D). The FOZ was measured and compared among the three groups at 6 mo postoperatively. The correlations between attempted corrections and anterior corneal surface curvature, corneal aberrations, Q value and the FOZ were analyzed. Results At 6 mo postoperatively, the mean FOZ was 5.06 ± 0.24mm in the control group, 5.19 ± 0.25mm in the moderate astigmatism group, and 5.35 ± 0.20mm in the high astigmatism group, with a statistically significant difference between the three groups (P < 0.001). The FOZ was significantly larger in the high astigmatism group than in the other groups, with statistically significant differences (p < 0.05,p < 0.001, respectively). Pearson correlation analysis showed that the changes in attempted equivalent spherical degrees, total corneal higher-order aberrations (HOAs), coma and spherical aberration changes were significantly negatively correlated with the FOZ among the three groups (all p < 0.05). Postoperative FOZ positively correlated with changs in the steep curvature (K2), mean curvature (Km), corneal astigmatism and Q value (all p < 0.01). Multiple linear regression analysis also suggested that the preoperative K2 was significantly positively correlated with the FOZ following the removal of other risk factors (p < 0.001). Conclusions Under the same programmed optical zone, high astigmatism eyes can obtain a larger FOZ and less induced coma. High curvature eyes can obtain a larger FOZ following transPRK.