Corneal healing after riboflavin ultraviolet-A collagen cross-linking determined by confocal laser scanning microscopy in vivo: early and late modifications

PURPOSE: To assess early and late micromorphological modifications of cross-linked corneas in vivo by means of Heidelberg Retinal Tomography (HRT) II confocal microscopy. DESIGN: Prospective nonrandomized open trial. METHODS: Micromorphological examination of 44 cross-linked keratoconic corneas was performed in vivo by HRT II confocal laser scanning microscopy. Riboflavin ultraviolet (UV)-A-induced corneal collagen cross-linking (CXL) was performed according to the Siena protocol: pilocarpin 1% drops 30 minutes before, topical anesthesia with lidocaine 4% drops 15 minutes before irradiation, mechanical scraping of epithelium (9-mm-diameter area), preirradiation soaking for 10 minutes in riboflavin solution 0.1% (Ricrolin, Sooft, Italy) applied every 2.5 minutes for 30 minutes, 30 minutes exposure to solid-state UVA illuminator (Caporossi; Baiocchi; Mazzotta, X-linker, CSO, Italy), 8-mm-diameter irradiated area, energy delivered 3 mW/cm(2). All patients were examined by confocal scans preoperatively and at the following times after treatment: one, three, and six months, and one, two, and three years. RESULTS: No damage to the limbal region was observed. Epithelial regrowth was complete after four days of soft contact lens bandage. The anatomy of the subepithelial plexus was restored one year after the operation with full corneal sensitivity. Increased density of extracellular matrix in late postoperative period indicated cross-linked collagen to a depth of 340 microm expressed by a late demarcation line. CONCLUSION: In vivo confocal microscopy showed early and late modification of corneal microstructure after the treatment. The three-year stability of CXL recorded could be related to increased cross-links formation, synthesis of well-structured collagen and new lamellar interconnections.