Diabetes Mellitus Affects Biomechanical Properties of the Optic Nerve Head in the Rat

Background: To investigate the effect of diabetes on the biomechanical behavior of the optic nerve head (ONH) and the peripapillary sclera (ppSc) in streptozocine-induced diabetic rats.

Methods: Diabetes mellitus was induced in 20 Wistar rats using streptozocine. Twenty-five nondiabetic rats served as controls. Eyes were enucleated after 12 weeks and 2 strips of one eye were prepared containing ONH or ppSc. The stress-strain relation was measured in the stress range of 0.05-10 MPa using a biomaterial tester.

Results: At 5% strain the stress of the ONH in diabetic rats was 897±295 kPa and in the control group it was 671±246 kPa; there was a significant difference between both groups (p=0.011). The stress of the diabetic ppSc (574±185 kPa) increased compared to that of the nondiabetic ppSc (477±171 kPa), but this did not reach statistical significance (p=0.174). The calculated tangent modulus at 5% strain was 11.79 MPa in the diabetic ONH and 8.77 MPa in the nondiabetic ONH; there was a significant difference between both groups (p=0.006). The calculated tangent modulus at 5% strain was 7.17 MPa in the diabetic ppSc and 6.12 MPa in the nondiabetic ppSc, without a statistically significant difference (p=0.09).

Conclusion: In contrast to the ppSc, the ONH of diabetic rats showed a significant increase in stiffness compared to nondiabetic rats, which might be explained by nonenzymatic collagen cross-linking mediated by advanced glycation end products due to high blood glucose levels in diabetes. Further studies are needed to investigate if these biomechanical changes represent a detrimental risk factor for intraocular pressure regulation in diabetic glaucoma patients.