Evidence that vascular factors contribute to the pathogenesis and development of glaucomatous optic neuropathy continues to accumulate. A higher than expected prevalence of systemic vascular disorders in individuals with glaucoma has been documented. New sophisticated in vivo analysis techniques, such as ultrasound color Doppler imaging, suggest that decreased blood flow velocity and increased vascular resistance are present in the vessels serving the optic nerve of human subjects with glaucoma, implying the presence of either organic or functional vascular disorders in these individuals. Recognizing that different analysis techniques have led to conflicting observations, experimental models have been developed to provide an additional tool with which to interpret the effects of compromised optic nerve perfusion