Hydration behavior of porcine cornea crosslinked with riboflavin and ultraviolet A

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Abstract
PURPOSE: To examine the influence of a new crosslinking treatment on corneal swelling properties that correlate with the degree of crosslinking. SETTING: Department of Ophthalmology, Vivantes-Klinikum Neukölln, Berlin, Germany. METHODS: Twenty freshly enucleated porcine eyes were crosslinked by applying the photosensitizer riboflavin and ultraviolet-A (UVA) light (370 nm, 3 mW/cm2) for 30 minutes. After the eyes were treated and incubated for 24 hours in a moist chamber, 15 eyes were examined by biomicroscopy and optical coherence tomography (OCT); 5 eyes were examined by light microscopy. Five control eyes were included. RESULTS: Using light microscopy, a characteristic swelling pattern with 3 zones was identified in the crosslinked porcine cornea: an anterior intensely crosslinked zone of 242 μm, an intermediate partially crosslinked zone of 238 μm (hydration factor 2.2), and a noncrosslinked posterior zone of 1355 μm (hydration factor 2.7). A condensed OCT signal was demonstrated in the treated portion of the anterior stroma to a depth of 520 μm with a pronounced line at 540 μm, correlating with the combined anterior and intermediate layers after hydration in the histological analysis. In the nonhydrated state of the crosslinked cornea, the anterior zone was deduced to be 242 μm; the intermediate zone, 109 μm; and the posterior zone, 501 μm. Therefore, the maximum depth of the crosslinking effect was 351 μm. CONCLUSIONS: Collagen crosslinking using riboflavin and UVA led to a significant change in the swelling behavior of the anterior stroma, confirming prior findings that the crosslinking effect is strongest in the anterior half of the stroma. Crosslinked cornea did not induce a specific signal on OCT, and OCT is therefore not suited for clinical controls of the crosslinking effect.