Ischemia is suspected in the pathophysiology of several eye diseases including glaucoma. The most direct way to study ischemia is through blood flow and circulatory studies and these have shown abnormalities in glaucoma and other eye diseases. However, blood flow changes per se do not necessarily indicate an unhealthy situation; blood flow indeed varies substantially in healthy tissues. The main metabolic consequence of ischemia is hypoxia and any harmful consequence of ischemia must include hypoxia at some point in time. Therefore, oxygen measurements are a direct way to study pathogenesis in ischemic diseases. Tissue damage would involve hypoxia and lack of hypoxia is not fully consistent with ischemic pathophysiology. The fact that hypoxia has to date not been found in glaucoma patients, suggests that ischemia may not be involved in the pathophysiology of glaucoma. The abnormalities in blood flow and oxygenation seen in glaucoma may be secondary to tissue atrophy, rather than the cause of the disease. Further studies, especially in patients with progressive glaucoma and high intraocular pressure will clarify the issue.