Optic Neuritis

Optic neuritis is an inflammation that affects the myelin lining of the optic nerve, which transmits visual stimuli to the brain. The optic nerve is a nerve tract of axons that originate in the ganglion cells of the retina in the back of the eye. Nerve tracts are the information pathways in the brain. The "optic nerves" are the only nerve tracts not located entirely within the brain. The optic nerves carry visual information from the retina 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 20 to 40 years of age. There is a strong female predominance. The annual incidence is approximately 6.4/100,000.

The precise cause of optic neuritis is unknown, but most cases are thought to be a type of autoimmune disorder. The immune system is generally used by the body 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 and destruction of the protective myelin sheath that coats and insulates the optic nerve, plus direct damage to the nerve axons results in loss of vision, which may be temporary or permanent.

Optic neuritis is frequently an indication of multiple sclerosis (MS), a disease in which the immune system attacks the myelin sheath covering nerve fibers in the brain and spinal cord, resulting in inflammation and nerve damage. Optic neuritis typically resolves initially but often recurs.

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 any first episode of optic neuritis. Various studies have shown that approximately 50% of patients who have optic neuritis for the first time will have magnetic resonance imaging (MRI) brain and/or spinal cord abnormalities consistent with MS at the time of the initial optic neuritis.

Neuromyelitis optica is another autoimmune condition in which demyelination occurs both in the spinal cord and both optic nerves but often sparing the brain. In this infrequent condition, the patient can experience weakness or paralysis in the limbs and/or bladder and bowel dysfunction, as well as bilateral loss of vision.

Certain bacterial infections (including Lyme disease, cat scratch fever, and syphilis, as well as viral infections such as measles, mumps, herpes simplex, and herpes zoster) can cause optic neuritis.

Other diseases (including sarcoidosis and systemic autoimmune disorders such as lupus) can cause optic neuritis.

Some drugs (including quinine, tetracycline, linezolid antibiotics, amiodarone, ethambutol, and isoniazid) have been associated with the development of optic neuritis. The phosphodiesterase type 5 inhibitors, such as Viagra, may cause damage to the optic nerve from inadequate blood supply (ischemia), rather than primary inflammation.

Approximately one-half of initial cases of optic neuritis have an unprovable cause and are described as idiopathic. These cases are presumed to be an inflammatory reaction developing 1 week to 1 month following an upper respiratory viral infection.

There are a variety of conditions that can affect the optic nerve, causing symptoms like optic neuritis. These include various optic neuropathies due to infection, trauma, hereditary conditions, toxic or nutritional problems, excessive use of nicotine or alcohol, compressive lesions of the optic nerves, and vascular diseases, including arteritic optic neuropathy, diabetes, and glaucoma. Treatment of these optic neuropathies is directed at the underlying disease.

Optic neuritis risk factors include trauma, hereditary conditions, toxic or nutritional problems, compressive lesions of the optic nerves, and vascular diseases, including arteritic optic neuropathy, diabetes, and glaucoma.

Symptoms of optic neuritis

The major symptom of optic neuritis is vision loss, usually in one eye, often developing within hours to a couple of days and peaking in 1-2 weeks. It may vary from a small area of blurring to complete blindness. Affected individuals may also notice distorted vision, inability to distinguish certain colors (dyschromatopsia), loss of contrast, and washed-out or less vivid vision than normal. Symptoms may be worsened by heat (Uthoff's phenomenon) 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. The intensity of the pain usually follows the course of the vision loss, decreasing and disappearing within 1-4 weeks.

Because optic neuritis usually affects one eye, patients may be unaware of subtle visual loss or changes in color vision until they or doctors close or cover the healthy eye.

Signs of optic neuritis

The most characteristic findings on examination include reduced visual acuity (typically 20/25 to 20/200), a measurable change in peripheral vision, decreased perception of brightness in the affected eye, and loss of color vision out of proportion to the loss of visual acuity. A disturbance in the reaction 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 optic nerve head can easily be visualized with fundoscopy, a painless procedure using an ophthalmoscopeope. In one-third of the cases, there is visible swelling of the optic nerve head, and there may be enlargement of the blood vessels around the nerve. This condition is called papillitis. In about two-thirds of patients, the inflammation is entirely behind the eye (retrobulbar), causing no visible changes when the physician examines the optic nerve with an ophthalmoscope. This is called retrobulbar neuritis.

Swelling of the head of the optic nerve can also be seen with papilledema, which sometimes occurs with increased intracranial pressure. In papilledema, visual acuity is usually not affected.

An ophthalmologist is a medical doctor who specializes in the diagnosis and treatment of eye disease. Ophthalmologists diagnose and treat optic neuritis, often in conjunction with a neurologist or family physician. A neuro-ophthalmologist is a medical doctor who subspecializes in the connections between the eye and the brain. Other specialists are involved based on any underlying diseases.

Optic neuritis is suspected based on the characteristic history of eye pain and vision loss. The standard exam includes visual acuity, pupillary reduction, visual field evaluation, color vision testing, and visualization of the optic disc by direct and indirect ophthalmoscopy.

A person experiencing a first episode of optic neuritis should undergo an MRI of the brain to detect central nervous system lesions associated with MS. If there is active brain inflammation, single or multiple brain lesions may be seen which light up (enhance) with injection of contrast material. The MRI may also show an enlarged optic nerve or inflamed optic nerve sheath.

Visual symptoms usually progress for the first few weeks and then start to improve within the first month. If the course of recovery is not typical, further testing can be performed to look for more unusual causes of optic neuritis/neuropathy.

If a definite cause (such as infection or underlying other disease) is determined, appropriate therapy for that cause is instituted.

The Optic Neuritis Treatment Trial, a multicenter randomized trial with 15 years of follow-up, showed that oral corticosteroids (prednisone) had no benefit on recovery to normal visual acuity. High-dose intravenous steroids, which involve some risks and can have significant side effects in some patients, including elevated blood sugar, depression, and insomnia. In the trial, high-dose intravenous steroids did speed up the initial recovery of vision in the acute phase. However, there was no conclusive evidence that intravenous steroids had any long-term benefit on visual acuity, visual field, or contrast sensitivity five years later.

Although there is no evidence that the use of oral nonsteroidal anti-inflammatory drugs (NSAIDs) have an effect on ultimate visual outcomes, they are effective in decreasing the pain on eye movement often associated with optic neuritis.

Various disease-modifying agents, including Glatiramer acetate (Copaxone), interferon beta-1a (Avonex, Rebif), interferon beta-1b (Betaseron, Extavia), mitoxantrone (Novantrone), and natalizumab (Tysabri), are used to decrease episodes of demyelination in patients with suspected or proven multiple sclerosis.

Intravenous immunoglobulin (IVIg) and plasma exchange (PLEX) are alternative immunomodulatory therapies that may offer additional benefit for acute optic neuritis.

Two monoclonal antibodies, eculizumab (Soliris) and Inebilizumab (Uplizna), and a recombinant humanized antibody, enspryng (Satralizumab-MWGE) have been recently FDA approved for the treatment of neuromyelitis optica.

Good nutrition and hydration, avoidance of tobacco, and refraining from vigorous exercise or over-heating is often recommended during the acute phase of optic neuritis.

The prognosis for and the time that the optic neuritis lasts depend on the underlying cause. Most episodes resolve spontaneously, with the return of vision in two weeks to three months. About 90% of people with optic neuritis will recover most of their vision within six months of onset. However, about 14% will have a recurrence of optic neuritis in the affected eye, and 12% will develop optic neuritis in the other eye within 10 years. If the patient has one or more abnormal lesions on the MRI, the risk of MS within 15 years is 72%.

Since almost 50% of optic neuritis is likely a result of a post-viral immune reaction, minimizing your risk of acquiring a viral respiratory infection decreases your risk of optic neuritis. It is impossible to avoid exposure to respiratory viruses, but research has shown that frequent hand-washing and attempting to not touch one's face without first washing one's hands decreases the incidence of the common cold. Teaching children to cover their mouths and noses when sneezing and instructing them on personal hygiene can also decrease the chances of the upper respiratory virus spreading within families.

In patients with recurrent optic neuritis secondary to multiple sclerosis, there are approved disease-modifying agents that reduce disease activity and disease progression for many people with relapsing forms of MS, including relapsing-remitting MS, as well as progressive forms of MS in those people who experience relapses. These include injectable forms of interferon beta, glatiramer acetate, and the biologic monoclonal antibody, daclizumab. Oral medications include teriflunomide (Aubagio), fingolimod (Gilenya), and dimethyl fumarate.

Relapses of multiple sclerosis are sometimes treated with a three- to five-day course of intravenous high-dose corticosteroids such as methylprednisolone. Similar to the use of this regimen in treating acute optic neuritis, intravenous corticosteroids will often end the relapse more rapidly but do not have any effect on the long-term outcome of the disease.

American Academy of Ophthalmology
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