Effect Of A 2-Mm Incision On Keratometry And Visual Quality After Small-Incision Lenticule Extraction

Objectives: To analyze the effects of corneal changes on astigmatism and keratometry (including cylinder power and corneal axis), and to evaluate the effect of a 2-mm corneal incision in small-incision lenticule extraction (SMILE) surgery by comparing visual quality parameters before and 1 year after SMILE. Methods: A total of 40 myopic eyes underwent myopia correction with SMILE. The axis of corneal curvature and the axes of flat (k1) and steep keratometric power (k2) were assessed preoperatively and 1 year postoperatively in different scan areas (3 mm, 5 mm, and 7 mm). Optical quality parameters were analyzed simultaneously. A paired t-test was used to compare preoperative and postoperative results, and a P-value < 0.05 was considered significant. Results: Corneal astigmatism, including the cylinder power and the corneal axis, did not change significantly (P > 0.05). Both k1 and k2 decreased after surgery. The k1 and k2 axes showed slight deflection, and the results in the 5-mm scan area were significantly different (k1: P = 0.045; k2: P = 0.000). The gap between k1 and k2 (k1-k2) showed significant change only in the 5-mm optical zone (P = 0.031). High-order aberrations significantly increased postoperatively in each scan area (P < 0.05), while coma and spherical aberration significantly changed in the larger optical zone. The point spread function changed significantly in the 7-mm optical zone after surgery (P = 0.011). Conclusion: A 2-mm incision is an appropriate technique in SMILE surgery that provides an ideal optical result in the central optical zone; however, it causes axial dispersion of keratometry and a decrease of visual quality. Hence, the flat k1 location is suggested for the SMILE incision.