Impact of corrected refractive power on the corneal denervation and ocular surface in small-incision lenticule extraction and LASIK

PURPOSE: To evaluate the impact of corrected refractive power on the corneal denervation and ocular surface in small-incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). SETTING: Singapore National Eye Center, Singapore. DESIGN: Prospective study. METHODS: 88 eyes undergoing SMILE or LASIK were divided into low-moderate (manifest refractive spherical equivalent [MRSE] <−6.0 diopters [D]) and high myopic (MRSE ≥−6.0 D) groups. In vivo confocal microscopy and clinical assessments were performed preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively. RESULTS: In SMILE, high myopic treatment presented with significantly greater reduction in the corneal nerve fiber area (CNFA) and nerve fiber fractal dimension (CFracDim) compared with low-moderate myopic treatment (both P < .05). There was a significant and negative correlation between the corrected MRSE and the reduction in 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 < .05). In LASIK, a significant correlation between the MRSE and the changes in 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 < .05). Compared with SMILE, LASIK had greater reduction in CNBD and CNFA for every diopter increase in the corrected MRSE. High myopic SMILE, compared with low-moderate myopic SMILE, resulted in significantly lower tear break-up time at 1 and 6 months (both P < .05). The changes in CNFA and CFracDim were significantly associated with Schirmer test values (both P < .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.