Experimental and computational modeling of the posterior scleral shell of the normal and glaucomatous monkey eye
Description
Glaucoma is one of the three leading causes of blindness in the U.S., and significantly impairs visual function in 2% of Caucasian and 6% of black Americans over the age of 40. Elevated intraocular pressure (IOP) has long been assumed to play a causative role in glaucomatous damage to the optic nerve head because this neuropathy is most commonly seen in eyes with elevated IOP. We believe IOP is a principal contributing risk factor in glaucoma and susceptibility is determined by anatomic and physiologic factors which govern the biomechanical response of an individual eye to IOP The eye is a pressure vessel, subject to the effects of IOP-related stress at all levels of intraocular pressure. As such, one can model the biomechanics of the eye, employing the finite element method to determine the IOP-related stresses and strains present in the load-bearing tissues of the posterior pole. Finite element modeling requires a three-dimensional geometry of the load-bearing tissues, material properties for those tissues, and loading and boundary conditions To begin this investigation, we have determined the thickness and surface geometry of the sclera in the posterior pole of the perfusion-fixed monkey eye. We have shown that posterior monkey sclera thins in response to chronic exposure to moderately elevated IOP. We have determined the viscoelastic material properties of sclera from rabbit eyes and normal and glaucomatous monkey eyes. We have shown that the material properties of monkey sclera are altered by chronic exposure to elevated IOP. Through finite element modeling of a scleral tensile specimen, we have shown that the finite element method is valid for modeling scleral tissues under load and have validated our experimental measures of scleral material properties. Finally, we have shown that short-term exposure to moderate IOP elevations causes thinning in the posterior scleral shell and alters the viscoelastic material properties of the sclera This work establishes the foundation upon which future finite element models of the posterior pole will be built