Aberration compensation between anterior and posterior corneal surfaces after Small incision lenticule extraction and Femtosecond laser‐assisted laser in‐situ keratomileusis

Abstract Purpose To investigate the aberration compensation between anterior and posterior corneal surfaces after SMILE and FS ‐ LASIK . Methods Fifty‐five subjects (55 eyes) undergoing SMILE and 51 subjects (51 eyes) undergoing FS ‐ LASIK were enrolled in this study. Wavefront aberrations of anterior and posterior corneal surfaces and the whole cornea at 6 mm in diameter were measured using a Scheimpflug Camera preoperatively and one, three and 6 months postoperatively. The compensation factor ( CF ), where CF = 1 − (aberration of the whole cornea/aberration of anterior corneal surface), was calculated. Results Spherical aberration of the posterior surface and the whole cornea remained stable after SMILE . However, spherical aberration of posterior surface increased significantly at 6 months in the FS ‐ LASIK group. The total higher‐order aberration ( tHOA ) of the anterior surface and the whole cornea was lower at 6 months than at one and 3 months ( p = 0.001 and 0.001, respectively) in the FS ‐ LASIK group. Meanwhile, in the SMILE group, no significant difference in tHOA was found between various postoperative time points. There were significant decreases in the CF of tHOA compared with preoperative values in both groups. The CF of spherical aberration reduced significantly in both groups at 3 and 6 mm in diameter one, three and 6 months postoperatively. Significant decreases in the CF of vertical coma were found at three and 6 months postoperatively in the FS ‐ LASIK group compared with preoperative values at 6 mm in diameter ( p = 0.021 and 0.008, respectively). The change in CF (Δ CF ) of spherical aberration was smaller in the SMILE group than in the FS ‐ LASIK group at one and 3 months postoperatively ( p = 0.003 and p < 0.0001, respectively). The Δ CF of spherical aberration was significantly lower in moderately myopic subjects than in subjects with high myopia at 1 month in the SMILE group ( p = 0.041) and at one, three and 6 months in the FS ‐ LASIK group ( p = 0.014, 0.020, and 0.004, respectively). Conclusions The posterior corneal surface plays an important role in compensating for spherical aberration of the anterior corneal surface. The compensation mechanisms of spherical aberration and higher‐order aberration between anterior and posterior corneal surfaces were disrupted by the SMILE and the FS ‐ LASIK procedures. The change in the CF of spherical aberration was smaller in the SMILE group compared with the FS ‐ LASIK group, especially in subjects with high myopia.