OCT- versus Scheimpflug-based Total Corneal Power Measurements Changes in Myopic Astigmatic SMILE Procedures.

Purpose: To evaluate the value of total keratometry (TK) to estimate corneal power in eyes that underwent SMILE for treatment of myopia or myopic astigmatism in subgroups of low and high astigmatism.
Methods: The difference between preoperative and postoperative measurements of corneal power (ΔTCRP, ΔTK) was compared with the surgically induced refractive change at the corneal plane (ΔSE _co ) by Pearson correlation. Vector analysis of TCRP- and TK-derived astigmatism was performed to evaluate the corneal astigmatism. Single-angle plots were generated with the AstigMATIC tool for standard astigmatism vector analysis.
Results: Paired t -test revealed statistically significant differences in preoperative ( p = .02) and postoperative ( p = .0455) measurements between TK and TCRP in the group of high-level astigmatism and the postoperative low astigmatism group ( p < .01). No significant differences were found in preoperative data in the group of low-level astigmatism ( p = .60). The correlation of ΔSEco and TK (low astigmatism, R ²  = 0.978; high astigmatism R ²  = 0.980) was stronger than the correlation of TCRP 4.0 mm and ΔSEco (low astigmatism, R ²  = 0.743; high astigmatism R ²  = 0.959) in both astigmatic groups. The vector analysis demonstrated nearly identical results concerning the correction index (CI) for TK and TCRP. Comparing the difference vector (DV) between both parameters, TK-derived results were closer to the optimum.
Conclusions: The findings endorse TK as a reliable measure of corneal power after SMILE in patients with low and high astigmatism.