Purpose: The aim of this study is to determine the effect of variation of the exposure time of near-infrared irradiation on corneal stiffening after a bacteriochlorophyll derivative (WST11) with dextran (WST-D) application.
Methods: One hundred four paired eyes of 3-month-old New Zealand White rabbits were included in this study. Fifty-two eyes (ex vivo n = 34, in vivo n = 18) were mechanically deepithelialized, treated topically with WST-D, and irradiated at 10 mW/cm using a diode laser at 755 nm for 1, 5, or 30 minutes. Untreated fellow eyes served as controls. Corneoscleral rings were removed immediately after treatment (ex vivo), or 1 month after treatment (in vivo). Corneal strips were cut and underwent biomechanical stress-strain measurements.
Results: Ex vivo, the mean tangent elastic modulus was significantly higher in the treatment groups than in the control groups for 1, 5, and 30 minutes of irradiation, respectively, 6.06 MPa, 95% confidence interval (CI, 4.5-7.6) versus 14.02 MPa, 95% CI (10.2-17.8), n = 11, 4.8 MPa, 95% CI (3.9-5.7) versus 15.03 MPa, 95% CI (12-18.1), n = 11, and 7.8 MPa, 95% CI (5.6-10.02) versus 16.2 MPa, 95% CI (13.6-18.9), n = 11; P < 0.001 for all comparisons. In vivo, the mean elastic moduli in the treatment groups were significantly higher for 5 and 30 minutes of irradiation but not for 1 minute of irradiation, respectively, 11.4 MPa, 95% CI (8.5-14.2), versus 17.1 MPa, 95% CI (14.5-19.7), n = 5; P < 0.001, and 9.4 MPa, 95% CI (5.1-13.8) versus 16 MPa, 95% CI (13.1-19), n = 5; P < 0.01, and 11.3 MPa, 95% CI (6-16.6) versus 12.2 MPa, 95% CI (7.5-16.8), n = 5; P = 0.7.
Conclusions: WST-D/near-infrared treatment using shortened irradiation time (1 minute ex vivo and 5 minutes in vivo) results in significant corneal stiffening, and this might provide an alternative to the currently applied riboflavin/ultraviolet A cross-linking.