Ischemic optic neuropathy (ION)
Ischemic optic neuropathy is a major cause of blindness or significantly impaired vision, and there are few definitive answers regarding its cause, clinical features and treatment.
There are two types of ION: anterior (which is characterized by swelling of the optic nerve head) and posterior (in which there is no swelling).
Ischemic optic neuropathy (ION) is when blood does not flow properly to your eye’s optic nerve, eventually causing lasting damage to this nerve. With ION, you suddenly lose your vision in one or both of your eyes.
The optic nerve carries signals from your eyes to the brain. Your brain then turns these signals into the images you see. When blood flow to the optic nerve is reduced or blocked, the nerve does not get enough oxygen or nutrition. The optic nerve stops working properly, and eventually dies.
Anterior ischemic optic neuropathy due to inadequate perfusion of the posterior ciliary arteries that supply the anterior portion of the optic nerve produces sudden visual loss, usually with an altitudinal field defect, and optic disk swelling.
In older patients, it may be caused by giant cell arteritis (arteritic anterior ischemic optic neuropathy). The predominant factor predisposing to nonarteritic anterior ischemic optic neuropathy, which subsequently affects the fellow eye in around 15% of cases, is a congenitally crowded optic disk. Other predisposing factors are systemic hypertension, diabetes mellitus, hyperlipidemia, systemic vasculitis, inherited or acquired thrombophilia, interferon-alpha therapy, obstructive sleep apnea, and phosphodiesterase type 5 inhibitors.
Ischemic optic neuropathy, usually involving the retrobulbar optic nerve and thus not causing any optic disk swelling (posterior ischemic optic neuropathy), may occur with severe blood loss; nonocular surgery, particularly prolonged lumbar spine surgery in the prone position; severe burns; or in association with dialysis. In all such situations, there may be several contributory factors.
If blood flow to your optic nerve is reduced, your vision will darken for a few seconds or minutes then return to normal. This is called a transient ischemic attack (TIA). This kind of attack can happen before ION begins. If you have TIA symptoms, call your ophthalmologist or primary care doctor right away. Finding and treating the problem as soon as possible can help prevent further vision loss from ION.
Arteritic anterior ischemic optic neuropathy necessitates emergency high-dose systemic corticosteroid treatment to prevent visual loss in the other eye. It is uncertain whether systemic or intravitreal corticosteroid therapy influences the outcome in nonarteritic anterior ischemic optic neuropathy or whether oral low-dose (~81 mg daily) aspirin reduces the risk of fellow eye involvement. In ischemic optic neuropathy after nonocular surgery, treatment of marked anemia by blood transfusion may be beneficial.