Compensatory Corneal Epithelial Thickness Changes after Myopic Photorefractive Keratectomy Imaged with Ultra High Resolution AnteriorSegment Optical Coherence Tomography

Purpose: To evaluate how corneal epithelium thickness changes after myopic Photorefractive Keratectomy (PRK) relate to the magnitude of myopic correction, the diameter of the Optical Zone (OZ) and the incidence of regression in the early postoperative period. Setting: Tertiary referral center Design: Prospective longitudinal cohort study Methods: Twenty-two eyes of 11 patients with mean manifest spherical equivalent of -4.75 ± 1.69 D underwent PRK between November 2016 and March 2017. Epithelial thickness profiles were evaluated preoperatively and at 1, 3 and 6 month’s postoperatively using ultra-high resolution anterior segment OCT. The relationship between post-operative epithelial thickness changes and the magnitude of myopic correction, the OZ diameter and the refractive outcomes was investigated prospectively. Results: Central epithelial thickening progressed during the first three postoperative months (p=0.045, between first and third postoperative month) and stabilized thereafter (p=0.980, between third and sixth postoperative month). A corresponding myopic shift of 0.13 D and an increase in mean K by 0.65 D were observed at three months postoperatively, which remained stable thereafter and did not affect the final refractive outcomes (mean postoperative spherical equivalent 0.14 ± 0.40 D). Central epithelial thickness increased proportionally with the amount of myopia treated (r=0.41, p=0.04) and reversely with the ablation zone diameter (r=-0.39, p=0.04). Conclusion: Corneal epithelial hyperplasia after myopic PRK is dependent on the preoperative myopic error and ablation zone diameter. Epithelial hyperplasia-induced regression did not have a negative effect on the overall refractive outcome. Synopsis: The degree of epithelial thickening and hyperopic shift post-PRK depends on the preoperative refraction and the optical zone diameter. The subsequent regression does not negatively affect the refractive outcome.