Combination of violet light irradiation and collagenase treatments in a rabbit model.

Purpose: To investigate the use of collagenase type II for generating a rabbit model of keratoconus and to evaluate the impact of violet light (VL) irradiation on the disease model.

Methods: Six Japanese White rabbits were used. After epithelial debridement, the collagenase group was treated with a collagenase type II solution for 30 min; the control group was treated with a solution without collagenase. Three rabbits also underwent VL irradiation (375 nm, irradiance 310 μW/cm) for 3 h daily for 7 days after topical collagenase application. Slit-lamp microscopy, steep keratometry (Ks), corneal astigmatism, central corneal thickness, and axial length were examined before and after the procedure. The corneas were obtained on day 7 for biomechanical evaluation.

Results: A significant increase in Ks and corneal astigmatism was observed in the collagenase and VL irradiation groups compared with the control group at day 7. No significant difference was found in the change in corneal thickness between the groups. The elastic modulus at 10% strain but not at 3% and 5% strain in the collagenase group was significantly lower than that in the control group. There was no significant difference in the elastic modulus at each level of strain between the collagenase and VL irradiation groups. The average axial length at day 7 in the collagenase group was significantly longer than that in the control group.

Conclusions: Collagenase type II treatment can mimic keratoconus with increased corneal keratometry and astigmatism. There was no significant difference in the observed elastic behaviour of normal and ectatic corneas under physiologically relevant stress levels. VL irradiation did not cause regression of corneal steepening in this model with short-term observation.