To evaluate the efficiency and safety of genipin collagen crosslinking (G-CXL) on rabbit corneas in vivo.

Forty healthy New Zealand white rabbits were randomly divided into 0.20% G-CXL, 0.25% G-CXL, standard UVA-CXL and normal control group.And the right eyes were treated in different grouping.No procedures were performed in the normal control group.The corneal curvature (Km) and central corneal thickness (CCT) of right eyes were evaluated before, 7 days and 14 days after crosslinking treatment.Cornea strips were harvested from the right eyes and tensile strain measurements were performed 7 days and 14 days after crosslinking treatment.The structure of corneal stroma was observed under light microscope (LM) and transmission electron microscope (TEM).

No statistically significant differences in Km were observed among different groups or different timepoints (F_group=0.301, P=0.825; F_time=1.287, P=0.284). Significant difference in CCTs was noticed among different time pionts (F_time=3.786, P=0.029). Compared with preoperative, the CCTs of all the groups were significantly increased 7 days after crosslinking (all at P<0.05). No significant difference in CCT was found among the groups (F_group=0.557, P=0.646). Seven days after crosslinking treatment, the Young's modulus at 10% strain was (11.96±5.74), (21.24±6.77), (18.76±3.34) and (11.56±4.37)MPa in 0.20% G-CXL group, 0.25% G-CXL group, UVA-CXL group and normal control group, respectively; the stress at 10% strain was (0.68±0.24), (1.20±0.25), (1.01±0.30) and (0.69±0.26)MPa, respectively; the Young's modulus and stress in 0.25% G-CXL group was significantly increased when compared with those in 0.20% G-CXL and normal control group (both at P<0.05). No significant difference in Young's modulus and stress was observed between 0.25% G-CXL group and UVA-CXL group (all at P>0.05). Forteen days after crosslinking treatment, Young's modulus at 10% strain was (16.65±3.19), (19.12±2.39), (22.83±4.38) and (12.70±2.72)MPa in 0.20% G-CXL group, 0.25% G-CXL group, UVA-CXL group and normal control group, respectively; stress at 10% strain was (0.83±0.12), (0.97±0.04), (1.23±0.30) and (0.65±0.20)MPa, respectively; the Young's modulus and stress in UVA-CXL group was significantly increased, when compared with 0.20% G-CXL group and normal control group (all at P<0.05). Statistical significance of stress was observed between 0.25% G-CXL group and UVA-CXL group (P=0.046). There is no significant difference in Young's modulus between 0.25% G-CXL and UVA-CXL group (P=0.090). LM showed the reduction of keratocytes existed in superficial stroma of 0.20% and 0.25% G-CXL groups, while the reduction of keratocyte was found in anterior and intermediate stroma of UVA-CXL group.In 0.20% and 0.25% G-CXL groups, the ultrastructure of keratocytes was normal except vacuole in some keratocytes.Keratocytes apoptosis was noticed in UVA-CXL group and keratocytes was normal in deep stroma under TEM.

0.25% has a similar biomechanics effect when compared to UVA-CXL.Moreover, histological observation proves a better safety of G-CXL in comparison of UVA-CXL.

Corneal collagen crosslinking; Genipin; Biomechanics; Keratocyte; Transmission electron microscope