Ulrastructural features of keratoconus cornea after cross-linking by riboflavin/UVA

Purpose In the present studies we assess the effects of collagen cross-linking on ultrastructure organisation of the corneal stroma of keratoconus human corneas. Methods One normal, one keratoconus (KC) and three cross-linked keratoconus corneas were analysed. One was treated with standard cross linking (SXL) and two with trans-epithelial collagen cross linking (TEXL). Penetrating keratoplasty was performed three months after treatment. All samples were fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer and processed for electron microscopy. Results The structure of SXL corneas was very similar to normal corneas in their hemidesmosomes, basement membrane (BM), Bowman’s layer (BW) and stromal lamellae that were not undulated. The architecture of TEXL corneas presented some differences. The BM was thick with degenerated hemidesmosomes. Bowman’s layer was disorganised at some places and replaced by thin filaments forming pannus. There were thin undulating lamellae in anterior, middle and posterior stroma. The keratocytes were embedded between undulating lamellae. Large amounts of abnormal PGs were attached around collagen fibrils. The parallel running lamellae were very thin. In some parts of the anterior stroma collagen fibrils were oriented (running) in random directions instead of running parallel. There were some parts of the stroma which showed a normal appearance. Conclusion The present studies demonstrate that corneal cross-linking leads to modifications in keratocytes and in the organisation of collagen fibril. The morphological changes might be correlated to the process of increase in biomechanical stability although there are differences between stromal structures treated by standard and trans