Change and Prediction in Intraocular Pressure after SMILE

Abstract

Objective: To evaluate the change in intraocular pressure (IOP) measured by non-contact tonometer after small incision lenticule extraction (SMILE), and to calculate a regression equation for estimating IOP. Methods: In this prospective case-series study, 87 patients (171 eyes) who underwent SMILE from April to December 2016 were enrolled. IOP, refractive error, central corneal thickness (CCT) and corneal curvature were measured preoperatively and postoperatively. We analyzed the relationship to different variables and calculated a correction formula for IOP after SMILE. Results: The mean IOP values were 13.6±3.1 mmHg and 8.7±2.1 mmHg before and after SMILE 6 months. Postoperative IOP decreased by 4.9±2.5 mmHg, and a t test showed that the difference was significant (t =25.93, P<0.001). Postoperative IOP was positively correlated with preoperative IOP and postoperative CCT (r =0.608, 0.237, P<0.01). Postoperative IOP was negatively correlated with preoperative spherical equivalent(SE), maximum lenticule thickness, and the rate of change rate of CCT and corneal curvature, △Km and △CCT (r =-0.190, -0.170, -0.200, -0.240, -0.250, -0.201, P<0.05). The multiple linear regression equation is IOPpos=5.021+0.414×IOPpre-0.018×maximum lenticule thickness (F=57.78, P<0.05, R2=0.400). Conclusions: Postoperative IOP is underestimated after SMILE. The proposed correction formula may be used to predict postoperative IOP measurement. Key words: myopia; astigmatism; small incision lenticule extraction; intraocular pressure; forecasting