Optic neuritis

Reviewed by Dr M J  Labuschagne M.B.Ch.B, M Med(Ophth), (OSSA member), University of the Free State, November 2010

Summary

• Optic neuritis is an inflammation of the optic nerve, leading to swelling and damage to the optic nerve.
• Symptoms include pain and vision loss.
• Usually this is temporary.
• In some cases, it may indicate an autoimmune disorder such as multiple sclerosis.

Alternative names

Optic neuropathy, papillitis, retrobulbar neuritis

Definition

Optic neuritis is an inflammation of the optic nerve, leading to swelling and damage to the nerve's outer covering, the myelin sheathand the nerve axons. This usually causes pain, as well as sudden vision loss or vision impairment in one eye. Optic neuritis can be considered in three categories, namely acute, chronic or asymptomatic (subclinical).

In most cases this is a temporary condition, although a decrease in vision may be permanent in less than 10% of cases.

In most cases opticneuritis may result from an autoimmune disorder, such as multiple sclerosis (MS) - a serious condition which causes nerve damage in the brain and spinal cord.

Causes  

The condition may result from the immune system attacking the myelin sheath. It's not certain what causes this; there may be a genetic component. Optic neuritis stemming from autoimmune disease usually affects younger adults (on average in their early thirties) - women more than men, and white people more than others.

Autoimmune disorders that can cause optic neuritis include:

• Multiple sclerosis (MS). Up to half of MS patients experience optic neuritis. People with optic neuritis are also at risk of developing MS later on, especially if an MRI (magnetic resonance imaging) scan shows that the neuritis is accompanied by brain lesions (myelin damage).
• Neuromyelitis optica. While this also causes inflammation in the optic nerve and spinal cord, it does not damage the brain to the same extent as MS. However, this neuritis tends to be more severe.

Other factors that may be involved in causing optic neuritis include:

• Bacterial infections, including Lyme disease, syphilis and cat-scratch fever
• Virus infections such as HIV, herpes and hepatitis B
• Inflammation of the cranial arteries (arteritis), which can block blood flow to the brain and eyes
• Sarcoidosis a multisystem granulomatous inflammation may affect the optic nerve
• Ischaemic conditions affecting the blood supply to the optic nerve
• Diabetes
• Hypertension
• Drugs, such as the tuberculosis drug ethambutol (Myambutol), Amiodarone
• Toxic reaction tomethanol
• In rare cases, radiation therapy to the head
• Nutritional deficiency, e.g. Vitamin B12

Symptoms and signs

Optic neuritis usually affects one eye, although sometimes both. Symptoms may include:

• Pain or discomfort around the orbit or in the eye, worsened by eye movement in 90% of patients. Pain usually grows worse during the course of a week, and then gradually disappears.
• Acute loss of vision in one eye, ranging from barely noticeable to severe. Vision may be blurred. This usually worsens over a few days, perhaps exacerbated by heat or exertion, and then disappears gradually over weeks or months.
• Change in colour perception. Reds, particularly, may appear less vivid than normal. One may not be aware of this until tested.
• Reduced constriction in the pupil in response to bright light

Diagnosis

If your doctor suspects optic neuritis, you will be referred to an ophthalmologist, who will examine your eyes with an ophthalmoscope to check for optic nerve swelling, changes in peripheral blood vessels of the retina and vitreous cells.

• Other eyes tests may test colour perception, the pupils’ reaction to bright light, reduction in contrast sensitivity or the slowing of electrical conduction along the nerve.
• MRI scans can determine whether there are brain lesions. An MRI can also rule out other conditions with similar symptoms, such as tumours.
• Blood tests can check for antibodies for neuromyelitis optica, and for inflamed cranial arteries.

Treatment

There is no known treatment for optic neuritis, but approximately 90% of patients recover to visual acuity of 0.5, or better, with time.

• In some cases, intravenous for 3 days followed by oral steroids for 15 days may reduce inflammation and quicken healing. However, they may not make a great difference to the outcome in the long term.  
• Disease modifying drugs, e.g.immunosuppressive therapy (Interferon beta-1a) may be prescribed to slow or prevent the development of multiple sclerosis, if this seems a likely outcome.
• If vision loss persists, plasma exchange therapy may help in some cases.

Prognosis

The prognosis is generally good, if there is no underlying autoimmune disease. Most people regain normal or near-normal vision. However, in some cases there is permanent sight loss, or recurring episodes.

People with multiple sclerosis or neuromyelitis optica may have recurrent attacks of neuritis. In such cases there is a poorer prognosis for retaining undamaged sight.

Complications

• Most people have some permanent damage to the optic nerve after a bout of optic neuritis, but this may be very slight.
• Steroid medication has side effects which may include a suppressed immune system and bone thinning.

When to call your doctor

Because there is a risk of sight loss with optic neuritis, you should contact your doctor if you feel:

• Eye pain or sight changes, including sudden loss of vision in one eye
• Limb numbness or weakness, which may indicate a neurological problem

If you have been diagnosed with optic neuritis, consult your doctor if you have new eye pain, deteriorating vision or persistent symptoms.

Reviewed by Dr M J  Labuschagne M.B.Ch.B, M Med(Ophth), (OSSA member), University of the Free State, November 2010