Vascular dysfunction in glaucoma

ABSTRACT Glaucoma, a leading cause of irreversible blindness, is characterized by progressive degeneration of the optic nerve and retinal ganglion cells (RGC). Glaucomatous damage might be caused either by elevated intraocular pressure (IOP), which could mechanically stress the optic nerve, or by reduced blood flow, which could impair function of the optic nerve. Lowering IOP is the only available treatment for glaucoma, but many patients continue to lose vision despite successful IOP reduction. Vascular abnormalities independent of IOP can occur in glaucoma patients, such as vasospasm and hypertension. While vascular dysfunction is associated with glaucoma pathophysiology, it remains uncertain whether blood flow impairment can be a target for intervention. Normalizing blood flow is a compelling novel treatment strategy for glaucoma. Our laboratory pioneered the application of multiparametric MRI to image high-resolution lamina-specific anatomy, quantitative blood flow, and function of the retina and optic nerve in rodents and in humans. This includes volumetric blood flow MRI of the retina, choroid, and optic nerve head, as well as diffusion MRI to measure optic nerve axonal integrity. Moreover, we have compelling preliminary data that blood flow is reduced in an established animal model of glaucoma and that chronic, mild hyperoxia treatment improves retinal function in glaucoma, supporting a role for blood flow impairment in glaucoma pathogenesis. Herein, we will utilize our MRI methods to further investigate the role of vascular dysfunction in glaucoma pathology by assessing a treatment to normalize blood flow in glaucoma. The goals of this proposal are to use our novel ocular MRI methods in an established mouse glaucoma model to: 1) evaluate whether a novel treatment strategy to increase blood flow can prevent glaucomatous damage and 2) evaluate whether combined treatments to lower IOP and normalize blood flow provide additional protection against glaucomatous progression. Our central hypothesis is that blood flow dysregulation contributes to glaucoma pathogenesis, so treatments to normalize blood flow could prevent damage and ultimately preserve vision in glaucoma. The impacts of this study will be i) novel insight into glaucoma pathophysiology and into the contribution of blood flow abnormalities to irreversible structural and functional damage, ii) establish novel retinal and optic nerve MRI as a method that provides unique, clinically relevant information on volumetric blood flow, and iii) establish an innovative treatment strategy for glaucoma of normalizing blood flow. The ultimate impact of this work would be to prevent blindness and vision loss due to glaucoma.