Ischemia is tissue damage caused by elimination of oxygen supply to that tissue.
The optic nerve is the wire that connects the the eye to the brain, transmitting electrical signals.
Optic neuropathy is damage to the optic nerve.
Ischemic optic neuropathy is divided into anterior (visible on an eye exam) and posterior (behind the eye). It is also divided into arteritic and non-arteritic. Arteritic is less common and is related to systemic inflammation in the blood. It can be diagnosed with ESR and c-reactive protein blood tests and/or temporal artery biopsy. Symptoms of arteritis include temporal pain on palpation, headache, and jaw pain on chewing. It happens in the very elderly and must be treated aggressively with systemic steroids.
Non-arteritic is more common and related to heart disease, high blood pressure, sleep apnea, and hypercholesterolemia. It is treated only by treating the underlying conditions.
The article is a nice review for ophthalmologists and other eye care providers.