Morphological Features of the Cornea in Patients with Initial Keratoconus after Simultaneous Photorefractive Keratectomy and Corneal Collagen Crosslinking. Part 1. Analysis of the Cellular Structure and Sub-basal Nerve Plexus of the Cornea

Objective: to present corneal morphological changes in patients with initial keratoconus during 12-month follow-up period after simultaneous transepithelial photorefractive keratectomy with accelerated ultraviolet collagen crosslinking. Patients and methods. The study included 30 patients/eyes aged 18–45 years with progressive stage 1 keratoconus, who underwent laser scanning in vivo confocal microscopy before and after treatment to measure the total, average, minimum and maximum lengths of corneal nerve fibres, as well as the sub-basal nerve plexus density; corneal optical coherence tomography with measurement of the demarcation line depth; Scheimpflug densitometry of the anterior-central layers of corneal stroma at 0–2 and 2–6-mm zones. The examinations were performed 1, 6 and 12 months after surgery. Results. Morphological changes observed by laser scanning in vivo confocal microscopy located in the anterior and middle stroma within 300 μm depth and were temporary: at 1 month — epitheliopathy, subepithelial fibroplasia, honeycomb-type lacunar edema and a sharp decrease in sub-basal nerve plexus density; at 6 months — partial regeneration of the keratocytes and sub-basal nerve plexus, reduction of the lacunar edema; at 12 months — nealrly complete restoration of corneal cellular structure and sub-basal innervation (sub-basal nerve plexus density — 80.5 % of preoperative data, total length of nerve fibres — 82 %). According to Scheimpflug densitometry, the highest values of corneal optical density was detected at 1 month after surgery and subsequently returned to baseline at 12 months, indicating reducing of postoperative corneal haze. According to anterior segment optical coherence tomography, the demarcation line depth was 198.5 (179.25; 214.5) μm visualized at 1 month postoperatively. Conclusion. Simultaneous transepithelial photorefractive keratectomy with accelerated corneal crosslinking can be considered as a safe and effective approach to managing initial keratoconus, that ensures morphological restoration of the cornea and minimal risk of severe fibroblastic complications during one-year follow-up period. Further research is needed to assess the long-term stability of the results.