Role of corneal epithelium in riboflavin/ultraviolet-A mediated corneal cross-linking treatment in rabbit eyes

Abstract

Purpose: To evaluate the role of corneal epithelium in riboflavin/ultraviolet-A (UVA) mediated corneal collagen cross-linking treatment.

Methods: Fifty New Zealand rabbits were divided into 5 groups: UVA treatment with or without corneal epithelium, UVA+riboflavin treatment with or without corneal epithelium, and control without any treatment. All rabbits were sacrificed after irradiation and subsequently 4 mm × 10 mm corneal strips were harvested for biomechanical evaluation.

Results: UVA irradiation alone did not enhance the maximal stress and Young's modulus of corneal specimens with (3.15 ± 0.56 mpa, 1.00 ± 0.09 mpa) or without (3.53 ± 0.85 mpa, 0.94 ± 0.21 mpa) the corneal epithelium, compared to specimens in the control group (4.30 ± 0.68 mpa, 1.03 ± 0.24 mpa). However, UVA irradiation combined with riboflavin significantly increased the maximal stress and Young's modulus of corneal specimens with (5.27 ± 1.09 mpa, 1.23 ± 0.23 mpa, P < 0.05) or without (7.16 ± 1.88 mpa, 1.42 ± 0.16 mpa, P < 0.05) corneal epithelium when compared to the control group. The maximal stress and Young's modulus of cornea in UVA+riboflavin and "epithelium-off" group were 35.9% and 15.4% higher compared to the UVA+riboflavin and "epithelium-on" group, respectively (P < 0.05).

Conclusions: Our study shows that UVA+riboflavin treatment significantly affects the biomechanical properties of the cornea with and without epithelial removal. However, corneas without epithelium seem to benefit more compared to corneas with the epithelium.

Figure 1

Evaluation of biomechanical properties of corneal strips was carried out on Instron 5544 system.

Figure 2

Histopathological analysis showed a successful removal of corneal epithelial cells in specified groups, with the integrity of Descemet's membrane (Hematoxylin eosin staining).

Figure 3

UVA irradiation alone did not enhance the maximal stress of cornea in epithelium-on (3.15 ± 0.56 mpa) or epithelium-off (3.53 ± 0.85 mpa) groups compared with those in control group (4.30 ± 0.68 mpa). The UVA irradiation combined with riboflavin significantly increased the maximal stress of cornea in epithelium-on (5.27 ± 1.09 mpa) or epithelium-off (7.16 ± 1.88 mpa) groups compared with those in control group (P < 0.05). The maximal stress of cornea in UVA+rib+nonepi group is 35.9% higher than that in UVA+rib+epi group (P < 0.05). Asterisk denotes significant difference with control group, unless otherwise specified.

Figure 4

UVA irradiation alone did not enhance Young's modulus of cornea in epithelium-on (1.00 ± 0.09 mpa) or epithelium-off (0.94 ± 0.21 mpa) groups compared with those in control group (1.03 ± 0.24 mpa). The UVA irradiation combined with riboflavin significantly increased Young's modulus of cornea in epithelium-on (1.23 ± 0.23 mpa) or epithelium-off (1.42 ± 0.16 mpa) groups compared with those in control group (P < 0.05). Young's modulus of cornea in UVA+rib+nonepi group is 15.4% higher than that in UVA+rib+epi group (P < 0.05). Asterisk denotes significant difference with control group, unless otherwise specified.