What is AON?

Acute optic neuritis (AON) is inflammation or demyelination of the optic nerve -- the nerve that transmits light and visual images from the retina, part of the eye, to the brain.

Eye diagram adapted from the National Eye Institute, National Institutes of Health website.

AON, or acute optic neuritis, is demyelination or inflammation of the optic nerve, the nerve that sends images from the retina to the brain. AON may cause a variety of symptoms that may vary from person to person, including:

• Blurry vision
• Vision graying or change in color saturation
• Loss of vision (usually in one eye)
• Pain in the eye

Optic neuritis is usually experienced as a rapid onset of blurring, graying (change in color saturation), or loss of vision, most often in only one eye. It is very seldom that AON affects both eyes at the same time. There may or may not be pain in the affected eye. The pain, if it occurs, may be of several types; dull and achy as if there were too much pressure, or sharp and stabbing as if something was piercing the eye. Vision loss usually reaches its worst effect within a few days of the onset of symptoms.

Approximately 66 percent of people diagnosed with multiple sclerosis (MS) will have at least one episode of AON. AON is often the first symptom of MS, although AON can occur in people who do not have MS.

AON may be treated with corticosteroids to help reverse inflammation and restore vision more quickly. In cases where symptoms are mild or lesions are not found with an MRI, the disease may be left untreated to resolve on its own. Although some cases of AON resolve on their own, some cases result in some level of irreversible vision loss. This damage is due to the loss of retinal nerve fibers leading from the eye to the brain. This study will assess if the study medication may reduce the loss of retinal nerve fiber layer thickness caused by AON.

Adapted from the NMSS website.