Corneal collagen fibril changes after ultraviolet a/riboflavin corneal crosslinking

The aim was to investigate the changes in collagen type 1 and type 3 in rabbit corneas undergoing corneal crosslinking with ultraviolet A and riboflavin and to analyze the possible mechanisms of corneal haze formation.

After removal of the central epithelium, the right corneas of 60 New Zealand rabbits were crosslinked with riboflavin and ultraviolet A, and 10 additional rabbits were used as the control group. The animals were killed 3, 7, 15, 30, 90, and 180 days postoperatively. Collagen type 1 and type 3 were analyzed using picrosirius red stain by means of polarized light microscopy. The biochemical changes in collagen type 3 at the time points indicated above were determined by Western blot analyses.

Collagen type 3 was significantly increased 30 days after corneal crosslinking compared with that in the control cornea, gradually increased until reaching its maximum value 90 days after riboflavin and ultraviolet A crosslinking, and then decreased until it returned to the normal state 180 days after crosslinking. There were no significant changes in collagen type 1 over time after corneal crosslinking. In agreement with the picrosirius red staining results, the western blot analyses showed that collagen type 3 was detected 15 days after the crosslinking treatment and continued to be present. However, 180 days after the crosslinking treatment, collagen type 3 could not be found in the crosslinked corneas.

These findings suggest that ultraviolet A/riboflavin crosslinking results in collagen type 3 synthesis and degradation, which may offer at least a partial explanation for the formation of corneal haze.