Ocular ischemic syndrome encompasses a spectrum of clinical findings that result from chronic ocular hypoperfusion. It is relatively uncommon, and the diagnosis may be difficult to make because of its variable presentations. The presence of an ocular ischemic syndrome always implies underlying severe carotid occlusive disease and may be its sole clinical manifestation. It may also result from other causes of reduced blood flow to the eye and the orbit such as systemic vasculitis. Besides visual loss and ocular/orbital pain, affected patients are also at risk for developing cerebral and myocardial infarction. Establishing the diagnosis is therefore essential with respect not only to visual prognosis but also to patient survival. Ophthalmologists have an important role in early diagnosis and in coordinating the systemic evaluation of patients. Referral to the neuroradiologist and the neurovascular specialist is warranted. We present the current knowledge on the ocular ischemic syndrome.