Effect of Collagen Cross-linking in Stromal Fibril Organization in Edematous Human Corneas

PURPOSE:To assess structural stromal modifications after riboflavin and UV-A exposure in edematous human corneas. METHOD:Fourteen eyes with corneal edema were enrolled in the study. In the cross-linking (CXL) group, 7 corneal buttons were obtained from 6 patients who underwent penetrating keratoplasty (PK) 7-90 days after the CXL treatment. The control group was composed of 7 corneal buttons with bullous keratopathy. After the PK, stromal modifications were investigated using immunofluorescence in all corneal grafts. All patients had at least 3 months of corneal edema and were in the eye bank list waiting for keratoplasty. RESULTS:All corneas in the treated group showed a pronounced lamellar zone of collagen fibers highly organized in the anterior stroma, but there was not complete homogeneity between the samples. Corneas with advanced disease and stromal fibrosis were less compacted than ones with mild disease severity. Similarly, those ones that underwent PK 3 months after CXL also showed a decreased effect compared with those with a reduced time between the CXL and the PK. DAPI staining demonstrated a complete fragmentation of keratocytes nuclei in the anterior stroma in all treated corneas, which were absent in the control group. CONCLUSIONS:Our study showed an immediate effect of CXL with a limited long-term sustainability. Cross-linked corneas had a pronounced anterior zone of organized collagen fibers. Even the treated corneas with advanced bullous keratopathy and stromal fibrosis had histological evidence of collagen fibers organization, but this effect seems to be decreased compared with corneas in initial stages of the disease.