Optic Neuritis

Eye anatomy. Image © A.D.A.M.

Optic neuritis is an inflammation of the optic nerve. The optic nerve is the bundle of nerve fibers that connects your eye to your brain. The optic nerve transmits visual information to the brain. The optic nerve is covered by a fatty material called myelin that acts as insulation. Myelin helps electrical impulses travel quickly along the nerve. It is commonly believed that optic neuritis develops when the body's own immune system attacks this tissue.

Most cases of optic neuritis occur in women who are between the ages of 20 and 40. 

Symptoms of Optic Neuritis

Optic neuritis often causes vision loss and pain upon moving the eye. This pain is caused by stretching of the inflamed optic nerve covering. Flashes of light may also occur with eye movement. Symptoms tend to worsen when body temperature increases. Vision loss is typically gradual, reaching its maximum within two weeks. The amount of vision loss is different among patients. Some patients also experience problems with depth perception.

Causes of Optic Neuritis

Optic neuritis can be caused by many diseases and conditions. Some people develop optic neuritis following an illness such as mumps, measles, or even a common cold. In others, the condition is closely related to multiple sclerosis. Some people who have an episode of optic neuritis develop multiple sclerosis later in life. Some cases of optic neuritis are called idiopathic.

This means that you have optic neuritis for an unknown reason or undetermined cause.

Other causes of optic neuritis include the following.

  • bacterial infections, such as syphilis or Lyme disease
  • viruses such as herpes or hepatitis B
  • sarcoidosis
  • cranial arteritis
  • certain chemicals and dugs

Clinical Signs of Optic Neuritis

Your eye doctor may detect signs of optical neuritis during a dilated eye exam.

He may see a swollen or elevated optic nerve head. Debris, cells or fluid from your immune system may also be present on the retina. Sometimes, you may notice symptoms before your optic nerve shows signs of swelling, a condition referred to as retrobulbar optic neuritis. Your doctor may also notice a difference in the way your pupils react to light. Also, your visual acuity may be reduced, and you may notice blind spots or dim areas in your field of vision. Color vision may also be affected.

Diagnosis of Optic Neuritis

To obtain an accurate diagnosis of optic neuritis, your doctor will perform a comprehensive eye exam after dilating your eyes, including a color vision test and a visual field test. Your doctor may order an MRI and additional blood tests to confirm the diagnosis. He or she may discover abnormalities during visual field testing, color vision testing, and visual acuity testing that will aid in the diagnosis. 

Treatment of Optic Neuritis

Many patients with optic neuritis improve without treatment.

Treatment often depends on how soon the condition is diagnosed after you first notice symptoms. In some cases, treatment includes the use of steroids to help reduce inflammation of the optic nerve. Steroid treatment usually involves intravenous steroids followed by oral steroids. A normal course of steroids is three days of IV steroids followed by a few days of tapering the medication. Some people suffer severe side effects while being treated with steroids. If you develop any sudden severe side effects, contact your doctor immediately. Normal side effects of steroid treatment can include the following:

  • difficulty sleeping 
  • stomach upset or nausea
  • a metal taste in the mouth
  • anxiety or irritability 
  • increased glucose levels (particularly in diabetics) 
  • thrush (a fungal infection) 

After an episode of optic neuritis, your vision may return to normal or close to normal within six months. 

What You Should Know

Optic neuritis sometimes recurs and requires retreatment. A small group of people has continued recurrence of the disease and requires ongoing treatment. Over time, about 50 percent of patients with optic neuritis will develop other neurological symptoms that may suggest the diagnosis of multiple sclerosis. Patients with more severe optic neuritis may have a condition called neuromyelitis optica. This condition requires diagnosis with a blood test.

Source:

Slamovits, Thomas L. and Ronald Burde. Neuro-ophthalmology, Textbook of Ophthalmology. Volume 6, ISBN 1-56375-099-6. Copyright 1994, Mosby-Year Book Europe Ltd.

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