Optic Nerve Head Quantification While Reducing Elevated Intracranial Pressure

Objective: The goal of this study is to examine in-vivo the effect of intraocular (IOP) and intracranial pressures (ICP) on the optic nerve head (ONH). Specific Aims: In this study, the investigators will quantify the structural changes in the ONH in subjects with elevated ICP while they are treated to reduce the elevated pressure. This process will occur in a stepwise fashion over a period of time determined by the clinical treatment plans. The investigators will apply controlled pressures to the eye during each step of ICP lowering while OCT images are obtained. Background: The effect of ICP on eye health has been an area of concrete research effort in recent years. The ability to acquire non-invasive and highly detailed information on both the eye and the brain using technologies such as magnetic resonance imaging (MRI) and optical coherence tomography (OCT) have paved the way to assess non-invasively the effect of ICP in-vivo. The ONH separates two pressurized compartments: the eyeball and the central nervous system. Situations in which ICP is elevated are often associated with papilledema, though the magnitude and the rate of change in ONH elevation in response to increased ICP or the reduction in ONH elevation in response to ICP treatments are yet to be determined. On the opposite side, glaucoma is a leading cause of blindness where elevated IOP is the leading risk factor, with clinical evidence suggesting the presence of ICP below the normal level in these subjects. The impaired balance between IOP and ICP leads to the deformation of the ONH, which triggers strangulation of the retinal ganglion cell axons when trespassing through the lamina cribrosa within the ONH on their way from the eye to the brain, leading to gradual axonal loss and irreversible visual impairment. Significance: Little is known about how the interaction of IOP and ICP pressure changes affect the macrostructure and microstructure of the optic nerve head structure. This information has a significant impact both for neurosurgical conditions with elevated ICP along with ocular conditions such as glaucoma and papilledema. The ability to gauge non-invasively changes in ICP will have a tremendous impact on neurosurgical management as it eliminates the need of longitudinal invasive measurements of ICP. The study will also improve the investigator's understanding of the pathophysiologic processes that lead to development of glaucoma as well as the response to treatment for subjects with papilledema. A better understanding of these processes will ultimately lead to improved detection and management of these conditions and a better understanding of ocular bio-mechanics.