Changes in the nonlinear and viscoelastic mechanical properties of the rat lamina cribrosa under chronic high intraocular pressure.

INTRODUCTION: The lamina cribrosa (LC) in the optic nerve head is the initial site of glaucomatous optic nerve injury. Under high intraocular pressure (IOP), the deformation of the LC compresses the retinal ganglion cell (RGC) axons passing through it. The influence of changes in the nonlinear and viscoelastic properties of the LC on its deformation cannot be neglected under high IOP. Therefore, investigating the changes in the nonlinear and viscoelastic mechanical properties of the LC under different durations of high IOP is of great significance. METHODS: A rat model with chronic high IOP was established by cauterizing the superior scleral vein and injecting 5-fluorouracil (5-FU) under the conjunctiva, producing sustained IOP elevation for 4, 8, and 12 weeks. Indentation tests were conducted on the rat LC. Then the loading segment and stress relaxation segment of the indentation curve were fitted separately. RESULTS: Compared with the control group, both the nonlinear parameters and viscoelastic parameters of the LC in experimental eyes decreased significantly. In contralateral control eyes, modest changes were also observed in some mechanical parameters, including the nonlinear parameters, relaxation modulus, and instantaneous modulus. DISCUSSION: The results indicated that long-term elevated IOP may contribute to the progression of glaucomatous optic nerve injury by altering the strain-dependent and time-dependent mechanical responses of the LC.