Confocal Comparison of Corneal Reinnervation after Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser In Situ Keratomileusis (FS-LASIK)

Meiyan Li,Anji Wei,Lingling Niu,Katherine Ni,Qihua Le,Jun Xiang,Bing Qin,Zimei Zhou,Xingtao Zhou,Weiping Ma,Suzanne Fleiszig

doi:10.1371/journal.pone.0081435

Abstract

PurposeTo evaluate corneal reinnervation, and the corresponding corneal sensitivity and keratocyte density after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK).MethodsIn this prospective, non-randomized observational study, 18 patients (32 eyes) received SMILE surgery, and 22 patients (42 eyes) received FS-LASIK surgery to correct myopia. The corneal subbasal nerve density and microscopic morphological changes in corneal architecture were evaluated by confocal microscopy prior to surgery and at 1 week, 1 month, 3 months, and 6 months after surgery. A correlation analysis was performed between subbasal corneal nerve density and the corresponding keratocyte density and corneal sensitivity.ResultsThe decrease in subbasal nerve density was less severe in SMILE-treated eyes than in FS-LASIK-treated eyes at 1 week (P = 0.0147), 1 month (P = 0.0243), and 3 months (P = 0.0498), but no difference was detected at the 6-month visit (P = 0.5277). The subbasal nerve density correlated positively with central corneal sensitivity in both groups (r = 0.416, P<0.0001, and r = 0.2567, P = 0.0038 for SMILE group and FS-LASIK group, respectively). The SMILE-treated eyes have a lower risk of developing peripheral empty space with epithelial cells filling in (P = 0.0005).ConclusionsThe decrease in subbasal nerve fiber density was less severe in the SMILE group than the FS-LASIK group in the first 3 months following the surgeries. The subbasal nerve density was correlated with central corneal sensitivity.

Highlights

The human cornea is densely innervated and richly supplied by bundled nerve fibers
We hypothesized that the reduction in corneal subbasal nerve density in patients who receive the Small incision lenticule extraction (SMILE) procedure would be less severe than the patients who receive femtosecond laser in situ keratomileusis (FS-LASIK)
All 40 patients in the current study were included in a population of 71 patients in another of our studies which focused on dry eye and corneal sensitivity after SMILE and FS-LASIK

Summary

Introduction

The corneal nerve fibers and related neurotrophins and neuropeptides play a large role in maintaining homeostasis of the ocular surface. Several neuropeptides and corneal nerve growth factors which regulate corneal epithelial proliferation, integrity, and wound healing, such as substance P and calcitonin gene-related peptide, were shown to be suppressed after refractive surgeries, [1] contributing to postoperative corneal hypoesthesia [2,3], dry eye [4,5], and LASIK-induced neurotrophic epitheliopathy [6]. SMILE technology has exhibited excellent efficacy, safety, and predictability [7,8,9]. In this flapless SMILE procedure, flaps are replaced with caps, significantly minimizing the incision access to the intrastromal lenticule [7,8,9] and, theoretically, transecting fewer superficial nerve fibers [10]. We hypothesized that the reduction in corneal subbasal nerve density in patients who receive the SMILE procedure would be less severe than the patients who receive femtosecond laser in situ keratomileusis (FS-LASIK)

Methods

Results

Conclusion