Corneal thickness, residual stromal thickness, and its effect on opaque bubble layer in small-incision lenticule extraction

Abstract

Purpose: To evaluate the effects of the central corneal thickness (CCT) and residual stromal thickness (RST) on the formation of opaque bubble layer (OBL) during small-incision lenticule extraction (SMILE).

Methods: A total of 345 eyes from Refractive Surgery Center database at Tianjin Eye Hospital that had been subjected to SMILE surgery and followed for 6 months were included in this study and divided into OBL and OBL-free groups. Preoperative, intraoperative, and postoperative data for all eyes were evaluated and analyzed using multivariate regression analysis. After adjustment for several confounding factors, potential associations of CCT and RST with OBL were elucidated by determining odds ratios (ORs) and 95% confidence intervals (CIs).

Results: In total, 22 of the 345 eyes developed various degrees of OBL during the femtosecond laser scanning phase of SMILE surgery. After adjustment for age, sex, and refractive errors, significant relationships were detected between CCT and RST and OBL formation (OR 1.04; 95% CI 1.02-1.06; OR 1.03; 95% CI 1.02-1.05, respectively, P < 0.001). Smooth curve fitting revealed an increased risk of OBL in the presence of an increased CCT or RST. However, visual outcomes were comparable between the two groups at both 3 and 6 months postoperatively.

Conclusions: The results suggest that OBL formation during SMILE surgery is more likely in eyes with a thicker cornea. CCT and RST can be considered independent risk factors for OBL formation. Although this phenomenon may disturb the surgical procedure, it is unlikely to affect the postoperative visual outcome.

Keywords: Central corneal thickness (CCT); Opaque bubble layer (OBL); Residual stromal thickness (RST); Small-incision lenticule extraction (SMILE).