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Optic Neuritis




Introduction

Optic neuritis is an inflammation of the optic nerve, the bundle of nerve fibers in your eye that transmits visual information to your brain. Pain and temporary vision loss are common symptoms of optic neuritis.

Optic neuritis usually develops due to an autoimmune disorder that may be triggered by a viral infection. In some people, signs and symptoms of optic neuritis may be an indication of multiple sclerosis, a condition resulting in inflammation and damage to nerves in your brain and spinal cord.

Most people who experience a single episode of optic neuritis eventually recover their vision. Treatment with steroid medications may speed up vision recovery.

Signs and symptoms

Optic neuritis usually affects one eye, although it may occur in both eyes simultaneously. Optic neuritis symptoms may include:
  • Pain. Most people who develop optic neuritis experience eye pain that's worsened by eye movement. Pain associated with optic neuritis usually peaks within one week and then goes away in several days.
  • Visual loss. The extent of visual loss associated with optic neuritis varies. Some people experience severe difficulty seeing, while others might not notice any changes in their vision. Vision loss, should it occur, usually develops over a day to a week and may be worsened by heat or exercise. Vision loss is usually temporary, but in some cases, it may be permanent.
  • Loss of color vision. Optic neuritis often affects the perception of colors. You may notice that the colors of objects, particularly red ones, temporarily appear "washed out" or less vivid than normal.


The signs and symptoms of optic neuritis may be indications of an autoimmune disorder called multiple sclerosis. In about 20 percent of people who eventually develop multiple sclerosis, optic neuritis is the first symptom.

Causes

The complex process of sight begins when light reflecting off an object enters the clear outer portion of your eyeball (cornea) and passes through the lens, which brings the light into focus on the nerve cell layer of your eye (retina). When light hits the retina, electrical impulses are generated and carried along the optic nerve to your brain, where the impulses are converted into visual information.

The optic nerve is a bundle of nerve fibers covered by a fatty insulated material called myelin, which helps electrical impulses travel quickly along the nerve. Optic neuritis in young adults is believed to most commonly develop when the immune system attacks myelin covering the optic nerve, resulting in inflammation and damage. It's not certain what causes your immune system to attack its own tissue. The following two autoimmune conditions are often associated with optic neuritis:
  • Multiple sclerosis. Multiple sclerosis is a disease in which your autoimmune system attacks the myelin sheath covering nerve fibers in your brain and spinal cord. In one large study of people with optic neuritis, the risk of developing multiple sclerosis following one episode of optic neuritis was 38 percent after 10 years. The evidence of brain lesions on MRI pictures increased the risk: People with optic neuritis and abnormal MRI scans had a 56 percent risk of developing multiple sclerosis after 10 years, while those with normal MRI scans had a 22 percent risk.
  • Neuromyelitis optica. Another autoimmune condition that may cause optic neuritis is neuromyelitis optica. In this condition, inflammation occurs in the optic nerve and spinal cord. Neuromyelitis optica isn't the same as multiple sclerosis, because neuromyelitis optica doesn't cause damage to the nerves in the brain as often as multiple sclerosis does. Optic neuritis arising from neuromyelitis optica tends to be more severe than optic neuritis associated with multiple sclerosis.
Other optic neuritis causes include:
  • Infections. Bacterial infections, including Lyme disease, cat scratch fever and syphilis, or viruses such as HIV, hepatitis B, and herpes can cause optic neuritis. In addition, some infections may lead to a type of optic neuritis, called neuroretinitis, which isn't believed to be associated with the risk of developing multiple sclerosis.
  • Cranial arteritis. This is an inflammation of the lining of the arteries in your head. Inflamed cranial arteries can block blood flow to your eyes and brain, which may cause permanent vision loss or a stroke. Cranial arteritis is most likely to occur in adults age 65 years and older.
  • Diabetes. Diabetes is a condition in which your body can't make or properly use insulin, a hormone that regulates the amount of sugar in your blood. People with diabetes are at an increased risk of developing disorders of the optic nerve.
  • Drugs. Some drugs have been associated with the development of optic neuritis. One of these drugs is ethambutol (Myambutol), which is used to treat tuberculosis.
Radiation therapy to your head is an uncommon cause of optic neuritis. In addition, any process resulting in inflammation or compression of the optic nerve, including tumors, nutritional deficiencies or toxins, can interfere with the nerve's ability to conduct electrical impulses. This may cause vision loss and other symptoms that may mimic optic neuritis.

Treatment

Optic neuritis usually gets better on its own. In some cases, steroid medications are used to treat optic neuritis, because they help reduce inflammation in the optic nerve. If you receive steroids, your treatment may involve:
  • Intravenous steroids. You'll likely receive steroid therapy by vein (intravenously) for several days. Intravenous steroid therapy may accelerate vision recovery, but it doesn't appear to affect the extent to which you'll recover your vision.
  • Oral steroids. After intravenous steroid therapy, you may take an oral steroid called prednisone for several weeks. Oral steroids usually follow an intravenous course of steroids, because using oral steroids alone to treat optic neuritis has been associated with an increased risk of recurrence.
In instances in which steroid therapy has failed and severe vision loss persists, a treatment called plasma exchange therapy may help some people recover their vision.

Preventing multiple sclerosis
If you have optic neuritis and you're at high risk of developing multiple sclerosis, you may benefit from drugs that help prevent multiple sclerosis. These drugs include interferon beta-1a (Avonex, Rebif) and interferon beta-1b (Betaseron). These injectable drugs are used to prevent or delay the development of multiple sclerosis in people with optic neuritis who have two or more brain lesions evident on MRI scans.

Prognosis
The prognosis following optic neuritis is generally good. Most people regain normal vision two to six months after an episode of optic neuritis. However, people with multiple sclerosis or neuromyelitis optica may experience recurrent attacks of optic neuritis sometime after they've recovered from the initial episode. Other people without any underlying conditions also may have recurrent optic neuritis; these people have a better prognosis for their vision in the long term than do people with neuromyelitis optica.


Information obtained from National Institute of Health
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