In Vivo Confocal Microscopy After Contact Lens-Assisted Corneal Collagen Cross-linking for Thin Keratoconic Corneas

PURPOSE: To study in vivo confocal microscopy (IVCM) after contact lens-assisted corneal collagen cross-linking (CACXL) in keratoconic eyes with thin corneas. METHODS: This prospective interventional case series included patients with progressive keratoconus with minimum corneal thickness less than 400 mu m after removing epithelium. CACXL was done once functional corneal thickness was confirmed to be 400 mu m or greater after applying a riboflavin-soaked, ultraviolet barrier-free contact lens. Postoperative IVCM at 1, 3, and 6 months was performed. RESULTS: Ten eyes underwent CACXL. Mean preoperative minimum corneal thickness after epithelial removal was 376 mu m (range: 364 to 397 mu m). IVCM at 1 month showed CACXL-induced apoptosis evenly distributed at 350 +/- 30 mu m measured from epithelial surface. The demarcation line between edematous stroma and deep stroma beyond 350 mu m that appeared unaltered was appreciable at 1 and 3 months but not at 6 months. Corneal reinnervation was visible at 3 months and was fully restored by 6 months. Regular endothelial mosaic was seen at all times. At 6 months, keratocyte repopulation of anterior stroma, disappearance of edema, and deposition of denser extracellular matrix surrounding activated keratocytes was seen with hyperreflective microbands still detectable. Average endothelial count was 2,135 +/- 56 cells/mm(2) preoperatively versus 2,190 +/- 41 cells/mm(2) at 6 months postoperatively. CONCLUSIONS: CACXL increases functional corneal thickness during ultraviolet light application, thus overcoming conventional pachymetric limitations of CXL. Cytotoxic effects of CACXL are similar to IVCM changes seen in conventional CXL and were concentrated in anterior and intermediate stroma up to 300 +/- 30 mu m without epithelium. Anterior segment optical coherence tomography should be performed after contact lens application and before ultraviolet light treatment to confirm an increase in functional thickness greater than 400 mu m. For thinner corneas, combination treatments should be evaluated.