[The effect of corneal biomechanical properties on opaque bubble layer in small incision lenticule extraction (SMILE)].

Objective: To investigate the influence of corneal biomechanical properties on opaque bubble layer (OBL) in small incision lenticule extraction (SMILE). Methods: In this nested case control study, 20 patients (31 eyes) were enrolled in OBL group, while 51 patients (98 eyes) were included in non-OBL group. The parameters were obtained by Pentacam HR and Corvis ST examinations. Independent t test was used to analyze the difference of corneal biomechanical parameters between the two groups and multivariable logistics regression was applied to analysis the influence of corneal biomechanical properties on OBL. Results: This study enrolled 129 eyes in 71 cases including 30 males and 41 females, with a mean age of (22.50±5.18) years old. It has shown that the spherical equivalent (SE) [(-4.64±1.33) and (-5.78±1.61) D], central corneal thickness (CCT) [(572±29) and (550±32)μm], residual stromal thickness (RST)[(356±31) and (325±36 μm)], and lenticule thickness (LT) [(96±23) and (115±25) μm] were significantly different between OBL group and non-OBL group ( t= 3.58, -3.43, -5.68 and 3.64, respectively, P< 0.05). There were significant differences in deflection amplitude at the first applanation and highest concavity (A1 DefA and HC DefA), deflection area at the highest concavity (HC DefArea), maximum deformation amplitude (DAmax), maximum deflection amplitude (DefAmax) and stiff parameter (SP) (108.85±13.77 and 100.19±14.13) between the two groups ( t= -2.75, 2.41, 3.62, 4.09, 2.22 and -2.99, respectively, P< 0.05). The OR and 95% confidence interval of SP in crude and adjusted logistics models were 1.04, (1.01-1.07) ( P= 0.005), and 1.01, (1.00-1.05) ( P= 0.426), respectively. Conclusions: The occurrence of OBL could be influenced by various corneal biomechanical factors. The thicker CCT, thicker RST and the stiffer cornea may increase the risk for the occurrence of OBL. Fully acknowledgement on the relationship between corneal biomechanics and surgical outcomes and evaluation of the occurrence of OBL in SMILE surgery is of great importance for improving the safety and predictability of SMILE. (Chin J Ophthalmol, 2019, 55:115-121) .