| It was proposed more than a century ago that vascular factor plays a role in the pathogenesis of glaucomatous optic neuropathy (GON). Proponents of the vascular theory consider GON as a consequence of insufficient blood supply due to increased intraocular pressure (IOP) or other risk factors reducing ocular blood flow (OBF), which is supported by accumulating evidence obtained from clinical observation, population studies, and animal experiments. Recent studies using modern technology to determine OBF in various ocular vasculature have demonstrated that, compared with normal controls, patients with either primary open angle or angle closure glaucoma have decreased blood flow, decreased flow velocity, and increased vascular resistance. The OBF reduction increases in extent as GON progresses, but it may occur before the nerve damage can be identified. With the IOP controlled, glaucoma eyes with reduced OBF are more likely to progress in GON than those without impaired OBF.
It is important to be aware that glaucoma medication that lowers IOP but simultaneously reduces OBF may unfavorably influence the disease outcome. Treatment modalities that reduce IOP without decreasing blood pressure or increasing ocular vascular resistance may increase OBF as a result of increased ocular perfusion pressure. Carbonic anhydrase inhibitor may increase retinal circulation by directly acting on the capillaries in addition to its IOP-lowering effect. The usefulness of other treatment such as ginkgo biloba extract in glaucoma management awaits more studies to confirm.
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