Optic Neuritis

What is optic neuritis?

Optic neuritis is inflammation of the optic nerve, the structure that connects the eye to the brain. The optic nerve consists of nerve tracts (axons) that originate in the retina of each eye. The optic nerve carries visual information from the retina to the nerve cells in the brain stem, where the information is relayed to the area of the brain that recognizes vision (the occipital cortex).
Optic neuritis can occur in children or adults and may involve either one or both optic nerves. Optic neuritis typically affects young adults ranging from 18-45 years of age, with a mean age of 30-35 years. There is a strong female predominance. The annual incidence is approximately 5/100,000, with a total prevalence estimated to be 115/100,000.

What causes optic neuritis?

The precise cause of optic neuritis is unknown, but it is thought to be a type of autoimmune disorder. The immune system is generally used to fight infection by creating a reaction that combats bacteria, viruses, fungi, and other foreign proteins. In autoimmune diseases, this reaction is mistakenly directed against a normal part of the body, creating inflammation and potential damage. In the case of optic neuritis, the optic nerve becomes swollen and its function is impaired. Inflammation of the optic nerve causes loss of vision because of the swelling and destruction of the protective myelin sheath that covers and insulates the optic nerve. Direct damage to the nerve tracts (axons) may also play a role in nerve destruction.
Optic neuritis most commonly 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 disease in which the immune system attacks the myelin sheath covering nerve fibers in the brain and spinal cord, resulting in inflammation and damage to nerve cells in the brain and spinal cord. Demyelinating optic neuritis is another term for this eye condition. In optic neuritis resulting from demyelinating disease, particularly multiple sclerosis, there may be recurrences of optic neuritis over time.
In 15%-20% of people who eventually develop multiple sclerosis, optic neuritis is their first symptom. The risk of developing multiple sclerosis following one episode of optic neuritis is approximately 50% within 15 years of the episode of optic neuritis. On MRI scanning, almost half of the patients with optic neuritis (and no history or clinical evidence of multiple sclerosis) have abnormal brain white matter changes consistent with multiple sclerosis. In patients undergoing MRI scans of the brain at the time of the initial attack of optic neuritis, the finding of brain lesions on MRI images increased the risk of development of later multiple sclerosis threefold versus people with normal MRI scans. However, almost half of patients with any brain lesions on MRI at the time of the initial episode of optic neuritis will not have developed multiple sclerosis 10 years later.
Another autoimmune condition that causes optic neuritis is neuromyelitis optica. In this unusual condition, inflammation occurs in the optic nerve and spinal cord but usually not within the brain as often as in multiple sclerosis. Optic neuritis arising from neuromyelitis optica is more severe than optic neuritis associated with multiple sclerosis.
There are many causes of optic neuritis unassociated with multiple sclerosis, including:

• Infections: Bacterial infections, including Lyme disease, tuberculosis, cat scratch fever, toxoplasmosis and syphilis, or viral infections such as HIV (human immunodeficiency virus), hepatitis B, and herpes zoster can cause optic neuritis. Bacterial meningitis, encephalitis, and sinusitis (all especially in children) may cause optic neuritis or optic nerve damage.
• Cranial arteritis: This is an inflammation of the lining of the arteries within the skull. 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 60-90 years of age. This condition is also known as temporal arteritis or giant cell arteritis (GCA).
• Diabetes: Diabetes is a condition in which the body cannot make or properly use insulin, a hormone that regulates the amount of sugar in the blood and other tissues. People with diabetes are at an increased risk of developing disorders of the optic nerve, including optic neuritis, most likely from decreased blood flow to the optic nerve.
• Sarcoidosis, pernicious anemia, Grave's disease, bee stings, and vaccinations may cause vision loss from optic nerve swelling.
• Autoimmune diseases (such as systemic lupus) may cause inflammation of blood vessels (vasculitis) nourishing the optic nerve.
• Drugs. Some drugs have been associated with the development of optic neuritis. These include ethambutol (Myambutol) and certain antibiotics.
• Toxins: Lead, methyl alcohol, quinine, and arsenic may cause vision loss and other symptoms that may mimic optic neuritis.
• Radiation therapy to the head is an uncommon cause of optic neuritis.
• Leber's hereditary optic neuropathy, an inherited form of vision loss that affects mostly males in their 20s or 30s, may cause optic neuritis.

However, the basic cause of optic neuritis is often unknown.
The term "optic neuropathy" is a more general term used to describe any condition that results in damage to the optic nerve. Optic neuritis is a specific type of optic neuropathy resulting from inflammation. Common noninflammatory causes of optic neuropathy include glaucoma, blocked or limited blood flow, direct trauma to the optic nerve(s), many neurological diseases, elevated intracranial pressure, primary and metastatic optic nerve tumors, nutritional deficiencies, and toxic exposure, including alcohol and tobacco, intraocular inflammation, and injuries. Trauma can interfere with the nerve's ability to conduct electrical impulses. All of these may cause vision loss and other symptoms that may mimic optic neuritis.

What are symptoms of optic neuritis?

The major symptom of optic neuritis is vision loss, frequently maximal within one or two days and varying from a small area of blurring to complete blindness. Affected individuals may also notice distorted vision, reduced color vision, loss of contrasts, and washed out or less vivid vision than normal. Loss of vision usually develops over the course of a day to two weeks and may be worsened by heat or exercise. Vision loss is usually temporary, but it may be permanent in some cases.
Most people who develop optic neuritis experience eye pain that is worsened by eye movement. Pain associated with optic neuritis usually peaks within one week and then goes away within several days.
Optic neuritis usually affects one eye, although it may occur in both eyes simultaneously. In cases where only one eye is affected, patients may be unaware of subtle visual loss or changes in the color vision until the doctor asks them to close or cover the healthy eye.

What are signs of optic neuritis?

The most characteristic findings on examination include reduced visual accuracy (acuity), a measurable change in peripheral vision, decreased perception of brightness in the affected eye, and a change in color vision (often out of proportion to loss of visual acuity). A disturbance in function of the pupil (afferent pupillary defect or APD) is usually detectable if the other eye is either unaffected or involved to a lesser degree.
The head (known as the disk) of the optic nerve can easily be visualized by an ophthalmoscope. If the optic disk is swollen, the condition is called papillitis. Otherwise, it is referred to as retrobulbar neuritis. In about two-thirds of patients, inflammation is entirely retrobulbar, causing no visible changes when the physician examines the optic nerve with an ophthalmoscope. In the other one-third, there is visible swelling of the optic nerve and there may be enlargement of the blood vessels around the nerve.

How is optic neuritis diagnosed?

Optic neuritis is suspected in patients with characteristic eye pain and vision loss. A complete medical examination, including chemical analysis of the blood can help rule out related diseases. Tests may include visual acuity testing, pupillary testing, visual field testing, color vision testing, and visualization of the optic disc by direct and indirect ophthalmoscopy.
A person with a first episode of optic neuritis usually undergoes an MRI of the brain to look for central nervous system lesions. MRI with gadolinium enhancement may show an enlarged, enhancing optic nerve. MRI may also help diagnose multiple sclerosis by demonstrating typical abnormalities in the brain.

What is the treatment for optic neuritis?

If a definite cause (such as infection or underlying other disease) is determined, appropriate therapy for that cause can be instituted.
In optic neuritis of undetermined cause or related to multiple sclerosis, vision often returns to normal within two to 12 weeks with no treatment but may also advance to a permanent state of partial or complete visual loss.
Treatment with steroid medications (cortisone medications such as prednisone [Deltasone, Orasone, Prednicen-M, Liquid Pred] and methylprednisolone, [Solu-Medrol]) may speed up vision recovery. Although treatment with steroids have little effect on the final visual outcome in patients with optic neuritis, patients treated initially with intravenous (IV) steroids have about one-half the risk of developing multiple sclerosis in two years as untreated patients do. This effect disappears by the third year of follow up. In addition, patients treated with IV steroids have fewer repeated attacks of optic neuritis than untreated patients.
Ophthalmologists treat patients with optic neuritis with either IV -- followed by oral steroids -- or no treatment at all. For those who are treated, the regimen typically includes three days of IV steroids, followed by about 11 days of oral steroids.
When optic neuritis is associated with MRI lesions suggestive of multiple sclerosis (MS), immunomodulator or immunosuppressive therapy may be prescribed to reduce the incidence of future attacks.

What is the prognosis for optic neuritis?

The prognosis depends on the underlying cause. Most episodes resolve spontaneously, with return of vision in two weeks to three months. Some people have repeat episodes of optic neuritis. Most patients with a typical history of optic neuritis and no underlying systemic disease, such as a connective tissue disease, recover vision, but more than one-quarter have a recurrence in the same eye or in the other eye. MRI is used to determine future risk of demyelinating disease.
Visual deficits caused by optic neuritis may worsen over a period of about seven days before vision typically stabilizes at that level for three to eight weeks. Gradual vision improvement then may occur. About 95% of people with optic neuritis will recover much of their vision within six months of onset. However, about 20% will have a recurrence of optic neuritis in the affected eye, and 15% will develop optic neuritis in the other eye within 10 years.
Complications arising from optic neuritis may include optic nerve damage. Most people have some permanent optic nerve damage following an episode of optic neuritis, but they may not experience any symptoms. Decreased visual acuity or vision loss may persist after optic neuritis has improved. Up to 10% of people with a history of optic neuritis have some degree of long-term vision loss. Steroid medications used to treat optic neuritis may suppress the immune system, perhaps causing the body to become more susceptible to infections. Long-term use of steroids may also cause thinning of the bones (osteoporosis) and other side effects.
Patients who have optic neuritis without a disease such as multiple sclerosis have a good chance of recovery. Optic neuritis caused by multiple sclerosis or other autoimmune diseases such as systemic lupus erythematosus has a poorer outlook.

Can optic neuritis be prevented?

In patients with an infectious cause of optic neuritis, eradication of the underlying infection will usually prevent further episodes.
In patients with a known immune disorder such as systemic lupus or vasculitis, treatment of the underlying disorder will usually prevent further episodes.
In patients with known multiple sclerosis, treatment of the multiple sclerosis may decrease the incidence of future attacks of multiple sclerosis, including optic neuritis. Current treatment includes high-dose intravenous corticosteroids during attacks of multiple sclerosis and chronic preventative therapy including immune-modulating drugs (interferon [Roferon-A, Intron-A, Rebetron, Alferon-N, Peg-Intron, Avonex, Betaseron, Infergen, Actimmune, Pegasys], glatiramer acetate [Copaxone], or natalizumab [Tysabri]), immunosuppressants (mitoxantrone [Novantrone], cyclophosphamide [Cytoxan], azathioprine [Imuran, Azasan], or methotrexate [Rheumatrex, Trexall]).
Non-approved therapies that have not shown definite benefit in preventing attacks of multiple sclerosis include plasmapheresis (plasma exchange) and intravenous immune globulin. There are a large number of drugs under study by medical investigators for the prevention of recurrent attacks and manifestations of multiple sclerosis, including optic neuritis, that have yet to receive FDA approval.
In patients with diabetes-related optic neuritis, lifestyle modification (weight control, dietary changes and exercise) plus blood sugar stabilization can decrease the incidence of future vascular complications of diabetes. There are no scientifically validated preventive measures for other types of optic neuritis. Anecdotal evidence suggests that maintaining a healthy lifestyle with proper attention to good nutrition, exercise, prevention of obesity, maintenance of emotional health and adequate rest, together with avoidance of toxins such as cigarettes, may prevent many diseases. Regular annual eye exams are critical to maintaining healthy vision. Early treatment of vision problems can prevent permanent optic nerve damage (atrophy).

Where can I find more information on optic neuritis?

American Academy of Ophthalmology
http://www.aao.org

Optic Neuritis At A Glance

• Optic neuritis is an inflammation of the optic nerve of either or both eyes, typically affecting young adults.
• It may be triggered by a viral infection, but it is also sometimes an indication of multiple sclerosis. Other causes include infections, autoimmune disease, and injury to the optic nerve.
• The symptoms of optic neuritis include vision loss, reduced color vision, and pain on movement of the eye.
• The diagnosis is made on the basis of the patient history and an examination by an ophthalmologist. Blood tests and MRI scan of the brain may be indicated.
• Most cases of optic neuritis improve over a period of weeks. Treatment with corticosteroids may hasten recovery.

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Medical Author:

Andrew A. Dahl, MD, FACS

Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

Source:Medicinenet.com.