Figure 4.

Schematic drawing of corneal crosslinking (CXL) using riboflavin as a photosensitizer and activated with UVA. (A) A normal corneal contour. The magnified view of the corneal stroma showed normal amount of the corneal cross-links. (B) Keratoconus represents a corneal disorder where central or paracentral cornea undergoes progressive thinning and steepening. Magnified view of the corneal stroma showed less cross-link bonds within the extracellular matrix of the stromal collagen (red bars). (C) Upon exposure of riboflavin to UV-A light, the number of covalent bonds between collagen molecules, and between collagen molecules and proteoglycans increased leading to the stiffening of the cornea. The PDT effects is mediated primarily through the generation of singlet oxygen.