The impact of corrected refractive power on corneal denervation and ocular surface in SMILE and LASIK

Abstract Purpose: To evaluate the impact of corrected refractive power on corneal denervation and ocular surface in SMILE and LASIK. Setting: Singapore National Eye Center, Singapore. Design: A prospective study. Methods: Eighty-eight eyes undergoing SMILE or LASIK were divided into low-moderate (MRSE<-6.0 D) and high myopic (MRSE≥-6.0 D) groups. In-vivo confocal microscopy and clinical assessments were performed preoperatively and 1, 3, 6, and 12 months postoperatively. Results: In SMILE, high myopic treatment presented with significantly greater reduction in corneal nerve fiber area (CNFA) and nerve fiber fractal dimension (CFracDim) compared to low-moderate myopic treatment (both P <0.05). There was a significant and negative correlation between the corrected MRSE and the reduction of corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length, CNFA and CFracDim after SMILE ( r =-0.38 to -0.66, all P <0.05). In LASIK, a significant correlation between the MRSE and the changes of CNBD, corneal nerve fiber total branch density, CNFA ( r =-0.37 to -0.41), and corneal nerve fiber width ( r =0.43) was observed (all P <0.05). Compared to SMILE, LASIK had greater reduction of CNBD and CNFA for every diopter increase in the corrected MRSE. High myopic SMILE, compared to low-moderate myopic SMILE, resulted in significantly lower tear break-up time at 1 and 6 months (both P <0.05). The changes in CNFA and CFracDim were significantly associated with Schirmer’s test values (both P <0.001). Conclusions: Postoperative corneal denervation was related to corrected refractive power in both SMILE and LASIK. With the same refractive correction, LASIK led to more prominent corneal denervation.