Ischemic optic neuropathy (ION) is a sudden loss of central vision, side vision or both due to a decreased or interrupted blood flow to the eye’s optic nerve.
In order to see, the optic nerve carries impulses from the eye to the brain, where they are interpreted as images. The optic nerve is made up of a million tiny, delicate nerve fibers that are like wires. Many blood vessels nourish the optic nerve with blood rich in oxygen and nutrition. Without a healthy, functioning optic nerve, vision would not be possible.
Some ophthalmologists may describe ischemia of the optic nerve as a “stroke at the back of the eye.” A “stroke" is an interruption of the blood supply to the brain or a nerve in the body. With ischemic optic neuropathy, vision loss occurs because the optic nerve has lost blood circulation. How much vision is lost depends on how much the optic nerve is affected.
Two types of ischemic optic neuropathy
There are two types of ischemic optic neuropathy, depending upon the part of the optic nerve involved:
Anterior ischemic optic neuropathy (AION): AION occurs when blood flow is interrupted to the front (anterior) part of the optic nerve (also called optic nerve head).
Posterior ischemic optic neuropathy (PION). PION is much less common and is a result of ischemia of the back (posterior) part of the optic nerve, located some distance behind the eyeball.
Most cases of ischemic optic neuropathy are a type of AION.
Types of AION
There are two different forms of the most common type of anterior ischemic optic neuropathy (AION):
This dangerous form of AION is caused by inflammation of the arteries supplying blood to the optic nerve. Arteritic AION, three times more common in women than men, affects those over the age of 55.
The inflammation of AION is associated with giant cell arteritis (GCA), a very serious, potentially life-threatening condition that requires immediate diagnosis, including blood work and biopsies of arteries in the temple area of the head to confirm diagnosis.
The majority of people with GCA have symptoms before vision loss, such as overall fatigue, fever, pain in the temples, neck pain, pain when chewing, and scalp pain.
(Another less common form of GCA has no symptoms). A key visual symptom with arteritic AION is temporary blurring or loss of vision before vision loss is permanent.
Fluorescein angiography, where a dye is injected and a series of rapid photographs are taken, may help confirm the blockage of blood flow in an arteritic AION.
Nonarteritic AION (NAION)
Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common form of AION. NAION can affect someone at any age, with about 10 percent of those affected younger than 45. Men and women are equally at risk.