In Vivo Imaging of Riboflavin Penetration During Collagen Cross-linking With Hand-held Spectral Domain Optical Coherence Tomography

PURPOSE: To compare the effect of complete versus grid-like epithelial removal on riboflavin penetration during collagen cross-linking (CXL) in vivo using hand-held spectral domain optical coherence tomography (OCT, Bioptigen Inc). METHODS: In this prospective, observational, comparative case series, patients with progressive keratoconus undergoing CXL with riboflavin and ultraviolet A (UVA) light were enrolled. Twenty eyes (20 patients) undergoing CXL using 0.1% riboflavin and UVA light (365 nm) were imaged intraoperatively at 30 and 60 minutes after starting the procedure, using hand-held spectral domain OCT. In 10 eyes, the epithelium was removed completely in the central 7-mm zone (complete removal group) whereas in the remaining 10 eyes, the epithelium was removed in a grid pattern, leaving behind intact islands of epithelium (grid-like removal group). The depth of hyperreflective band (representing penetration of riboflavin) in the anterior corneal stroma was measured. RESULTS: In the complete removal group, the hyper-reflective band was homogenous, extending to a mean depth of 54.2±5.2 μm and 72.4±7.1 μm at 30 and 60 minutes, respectively (P<.001). In the grid-like removal group, the mean depth of the hyperreflective band was uneven, being significantly more in the "epithelium off" areas (56.90±4.66 μm and 74.2±6.7 μm at 30 and 60 minutes, respectively) (P<.001) compared to the "epithelium on" areas (18.9±2.3 μm and 24.7±2.3 μm at 30 and 60 minutes, respectively) (P<.001). CONCLUSIONS: Epithelial removal appears to be an essential step prior to performing CXL, as an intact epithelium appears to block penetration of riboflavin in the anterior corneal stroma.