Microstructure of the Optic Nerve Head

INTRODUCTION The ocular disease glaucoma is the second most common source of blindness worldwide. Gradual, irreversible vision loss is a result of nerve damage in the optic nerve head; a collagen structure that provides support for the optic nerve and blood vessels that enter the posterior of the eye [1]. Glaucoma is clinically known to be correlated with high levels of intraocular pressure from the fluid within the eye; intraocular pressure [2]. The method in which intraocular pressure causes nerve damage has yet to be discovered. The laboratory of ocular biomechanics aims to study the eye as a biomechanical structure as a means to understand and ultimately prevent glaucoma progression. An increase of intraocular pressure causes stresses and strains on the optic nerve head that could result in deformation of the collagen support structure [3]. As the structure of the optic nerve head is better defined, calculating the deformation becomes possible. This deformation provides insight to what blood vessels or nerves are most affected by pressure changes, as well as what characteristics would make an eye more or less susceptible to glaucoma. The sclera is part of the collagen region that makes up the optic nerve head [1]. The collagen in the sclera is oriented in fiber bundles called crimp, termed because of its wave like appearance. Because collagen performs well under tension, the wavy bundles stretch under increasing pressures [3]. To measure the stretch of the crimp, the period of the wave is recorded similarly to how the period of a sine wave is measured. Tracking the length of the crimp period shows how the collagen is changing and therefore how the sclera is deforming.