Corneal power measurements by ray tracing in eyes after small incision lenticule extraction for myopia with a combined Scheimpflug Camera–Placido disk topographer

Purpose To evaluate the accuracy of the measurements of corneal power obtained by ray tracing with a combined Scheimpflug camera–Placido disk corneal topographer (Sirius) in eyes after small incision lenticule extraction for myopia (SMILE). Methods Retrospective cases study includes 50 eyes of 50 patients who underwent myopic SMILE. Mean value of simulated keratometry ( K post ), mean pupil power (MPP) (ray tracing, diameter of the entrance pupil range 3–6 mm), anterior and posterior corneal radius, and corneal thickness were obtained with Sirius topographer preoperatively and three months postoperatively, as well as cycloplegic refraction. True net power, equivalent keratometry readings, and Haigis equivalent power formula were calculated, and these measurements, MPP and K post , were compared with the corneal power calculated with the clinical history method (CHM). Results Corneal power measurements obtained with all methods were significantly different from CHM ( P < 0.001), except the value of MPP obtained at 5.5 mm ( P = 0.927). A good direct correlation was found between CHM and all measurements. The distribution of differences as compared with the CHM showed that the lowest difference corresponded to the value of MMP at 5.5 mm (− 0.002 ± 0.6). The Bland–Altman plots for the MPP at 5.5 mm showed 95% limits of agreement between − 1.1787 D and 1.1741 D. Conclusions MPP obtained by ray tracing within a diameter of entrance pupil of 5.5 mm could predict corrected corneal power derived from the CHM in eyes following SMILE surgery.