# Epithelial Thickness More Than 10 Years After Myopic Laser-Assisted In Situ Keratomileusis (LASIK) Compared With Matched Controls and Its Correlation With Preoperative Refractive Parameters

## TL;DR

This study found that 10+ years after LASIK surgery, the corneal epithelium is thicker in the central area but thinner in the periphery compared to non-surgeried controls.

## Contribution

The study provides new long-term data on corneal epithelial thickness changes after LASIK, extending beyond previously documented short- and mid-term periods.

## Key findings

- LASIK patients had a 2.3 µm thicker central epithelium compared to controls, with increased variability in thickness.
- Peripheral epithelium in LASIK patients was significantly thinner in nasal, inferior, and temporal regions.
- Higher preoperative myopia correlated with thinner peripheral epithelium, while thinner preoperative corneas showed greater central thickening.

## Abstract

Background

This study aimed to investigate corneal epithelial thickness (ET) in patients at least 10 years after laser-assisted in situ keratomileusis (LASIK) compared with a matched control group, using spectral-domain optical coherence tomography (SD-OCT).

Methodology

This retrospective study analyzed 125 eyes (68 patients) who underwent myopic LASIK between 1996 and 2014 and compared them with a control group of 150 eyes (76 patients) with no prior ocular surgery. The control group was matched to the LASIK cohort based on age, sex, postoperative sphere, and postoperative spherical equivalent (SEQ), and included only eyes with available OCT imaging and no history of ocular pathology or surgery. In addition, correlations were evaluated between preoperative sphere, SEQ, mean keratometry, and postoperative ET maps. Corneal pachymetry was measured at the 2-, 5-, 7-, and 9-mm optical zone diameters using the Avanti Widefield OCT (Optovue, Fremont, CA, USA). Corneal topography metrics such as central corneal thickness and keratometry were obtained using Pentacam HR (Oculus, Wetzlar, Germany).

Results

The LASIK group had greater ET by 2.3 ± 0.5 µm in the central 2-mm zone compared with the matched control group (p < 0.001), with consistently thicker epithelium across the 5-mm zone. In contrast, ET was significantly thinner in the nasal and inferior regions of the 7- and 9-mm zones, as well as the temporal region of the 9-mm zone (all p < 0.05). ET variability, maximum ET, and minimum-maximum ET were increased following LASIK compared with control (p < 0.001), whereas minimum ET was lower by 2.6 ± 0.6 µm (p < 0.001). Correlation analysis showed that both preoperative sphere and SEQ were positively correlated with ET in the 7- and 9-mm zones (all p < 0.05), whereas no significant correlations were observed in the central or paracentral regions. Preoperative central corneal thickness showed a modest negative correlation with ET in the 2- and 5-mm zones, the nasal and inferior-nasal regions of the 7- and 9-mm zones, and the temporal region of the 9-mm zone (p < 0.05).

Conclusions

Long-term follow-up of LASIK patients revealed sustained central and paracentral epithelial thickening, indicating that epithelial remodeling persists beyond the short- and mid-term periods documented in the literature. While the central and paracentral cornea remained thicker after LASIK than control, the periphery was thinner, predominantly in the nasal and inferior regions and extending to the temporal region at the 9-mm zone. Higher preoperative myopia was associated with thinner epithelium in regions of the peripheral cornea. In addition, thinner preoperative central corneas demonstrated greater epithelial thickening in the central and paracentral zones, suggesting that baseline corneal thickness may impact the magnitude of epithelial remodeling. The epithelial distribution pattern after myopic LASIK is non-uniform and may contribute to long-term refractive changes.