Optic Neuritis: Overview

Optic neuritis is a condition in which the optic nerve becomes inflamed and swollen, leading to an acute severe impairment of vision in the affected eye. The swelling may further lead to damage to the nerve fibers running through the nerve, causing permanent or temporary loss of vision in that eye. It is much more common in young female patients.

The incidence is 1-5/100 000 per year. Most patients are between 18 and 45 years of age. It may occur in many parts of the world. The highest incidence is seen in Northern Europe, Southern, and the central parts of the North American continent.

Causes

Optic neuritis may have many causes, such as:

• Autoimmune diseases such as systemic lupus erythematosus or Behcet disease
• Cryptococcosis
• Bacterial infections such as tuberculosis or syphilis
• Viral diseases such as viral encephalitis, rubeola or rubella
• Some types of respiratory infection
• Multiple sclerosis which leads to demyelination of the optic nerve

However, most cases of optic neuritis are idiopathic.

Symptoms

Optic neuritis can manifest as a sudden loss of vision in as short a period as one hour or over a few days. In a few cases, both eyes may be affected, especially in children. Other symptoms include:

• Abnormal pupillary reactions due to a relative afferent defect
• Loss of color vision
• Painful eye movement

Diagnosis and Treatment

Much of our present knowledge of optic neuritis was gained from the Optic Neuritis Treatment Trial (ONTT). Optic neuritis is diagnosed by a detailed eye examination and tests, including:

• Testing of color vision in both eyes since the “unaffected” eye may really have subclinical involvement
• Brain MRI to pick uppatchy demyelination of the optic nerve which indicates a higher risk of multiple sclerosis
• Testing of visual acuity
• Testing of the visual field or perimetry, which typically shows a general decrease, but may also show specific field defects
• Indirect ophthalmoscopy to examine the optic disc which is often normal in appearance, the swelling being confined to the retrobulbar part of the optic nerve. In other patients the disc is edematous.
• Tests to identify any underlying disorder
• Notes on atypical symptoms, which rule out the presence of multiple sclerosis and indicate the need for urgent identification of treatable causes of optic nerve inflammation

In most cases, the vision returns to normal as the swelling of the optic nerve reduces spontaneously over a couple of weeks.

Most patients are given corticosteroids orally or by intravenous injection to speed up the recovery. However, studies have shown that the final visual outcome remains unaffected by the administration of steroids, which have, indeed, been shown to increase the chances of a recurrence of the condition. Intravenous steroids do significantly reduce the risk of developing multiple sclerosis within 2 years, though the protective effect lessens thereafter.

Prognosis

Almost 8 of every 10 patients start to recover vision within 3 weeks, and most patients show some degree of continuing improvement over 12 months. About 5-10 percent of affected eyes fail to recover. When the optic neuritis is not caused by conditions such as autoimmune disease or multiple sclerosis, it has a better prognosis for visual recovery. However, even with the latter, some people recover useful vision. Overall recurrence rates are 35% over 10 years. Patients who will develop symptoms of multiple sclerosis at some point have double the risk of recurrence (48%) compared to others (24%).

Complications

Complications caused by optic neuritis may include significant vision loss as well as systemic complications like Cushing’s syndrome, caused by the use of steroids.

References

• https://medlineplus.gov/ency/article/000741.htm
• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3116540/
• https://nei.nih.gov/news/pressreleases/onttpressrelease
• http://www.chop.edu/conditions-diseases/optic-neuritis#.V6nrs_l97V0
• http://healthcare.utah.edu/healthlibrary/related/doc.php?type=134&id=44