The scleral inflation response of mouse eyes to increases in pressure

Glaucoma is one of the leading causes of blindness in the world. Evidence suggests that the stress generated in the eye wall by an elevated intraocular pressure plays a role in damaging the vision-transmitting retinal ganglions cells. However, the relationship between the connective tissue's mechanical properties and how it affects the cellular function is not understood. The purpose of this study was to measure the inflation response of intact C57/BL6 (control) mouse sclera to increases in intraocular pressure, comparing old (11 month) and young (2 month) animals. Mouse eyes were enucleated, mounted by the cornea to a custom fixture, cannulated and immersed in PBS. An active feedback, pressure-controlled syringe pump inflated the cannulated eyes in a series of load-unload and ramp-hold creep tests. A CCD video camera attached to a microscope imaged the expanding scleral surface at 0.5Hz. Scleral displacement was measured with a digital image correlation program. After testing, fresh tissue thickness measurements were taken on scleral slices at multiple locations. An optimized inverse finite element analysis was performed to fit a non-linear anisotropic material model to the experimental data, and material parameters are compared between groups.