Optic Neuritis

Symptoms might include:

• Pain. Most people who develop optic neuritis have eye pain that’s worsened by eye movement. Sometimes the pain feels like a dull ache behind the eye.
• Vision loss in one eye. Most people have at least some temporary reduction in vision, but the extent of loss varies. Noticeable vision loss usually develops over hours or days and improves over several weeks to months. Vision loss is permanent in some people.
• Visual field loss. Side vision loss can occur in any pattern, such as central vision loss or peripheral vision loss.
• Loss of colour vision. Optic neuritis often affects colour perception. You might notice that colours appear less vivid than normal.
• Flashing lights. Some people with optic neuritis report seeing flashing or flickering lights with eye movements.

Causes

The following autoimmune conditions often are associated with optic neuritis:

• Multiple sclerosis. Multiple sclerosis is a disease in which your autoimmune system attacks the myelin sheath covering nerve fibres in your brain. In people with optic neuritis, the risk of developing multiple sclerosis after one episode of optic neuritis is about 50% over a lifetime.
• Your risk of developing multiple sclerosis after optic neuritis increases further if an MRI scan shows lesions on your brain.
• Neuromyelitis optica. In this condition, the inflammation affects the optic nerve and spinal cord. Neuromyelitis optica has similarities to multiple sclerosis, but neuromyelitis optica doesn’t cause damage to the nerves in the brain as often as multiple sclerosis does. Still, neuromyelitis optica is more severe than MS, often resulting in a diminished recovery after an attack compared with MS.
• Myelin oligodendrocyte glycoprotein (MOG) antibody disorder. This condition can cause inflammation to the optic nerve, spinal cord or brain. Similar to MS and neuromyelitis optica, recurrent attacks of inflammation can occur. Recovery from MOG attacks is usually better than recovery from neuromyelitis optica.

When symptoms of optic neuritis are more complex, other associated causes need to be considered, including:

• Infections. Bacterial infections, including Lyme disease, cat-scratch fever and syphilis, or viruses, such as measles, mumps and herpes, can cause optic neuritis.
• Other diseases. Diseases such as sarcoidosis, Behcet’s disease and lupus can cause recurrent optic neuritis.
• Drugs and toxins. Some drugs and toxins have been associated with the development of optic neuritis. Ethambutol, used to treat tuberculosis, and methanol, a common ingredient in antifreeze, paints and solvents, are associated with optic neuritis.

Diagnosis

You’re likely to see an ophthalmologist for a diagnosis, which is generally based on your medical history and an exam. The ophthalmologist likely will perform the following eye tests:

• A routine eye exam. Your eye doctor will check your vision and your ability to perceive colors and measure your side (peripheral) vision.
• Ophthalmoscopy. During this examination, your doctor shines a bright light into your eye and examines the structures at the back of your eye. This eye test evaluates the optic disk, where the optic nerve enters the retina in your eye. The optic disk becomes swollen in about one-third of people with optic neuritis.
• Pupillary light reaction test. Your doctor may move a flashlight in front of your eyes to see how your pupils respond when they’re exposed to bright light. If you have optic neuritis, your pupils won’t constrict as much as pupils in healthy eyes would when exposed to light.

Other tests to diagnose optic neuritis might include:

• Magnetic resonance imaging (MRI). An MRI scan uses a magnetic field and pulses of radio wave energy to take pictures of your body. During an MRI to check for optic neuritis, you might receive an injection of a contrast solution to make the optic nerve and other parts of your brain more visible on the images.
• An MRI is important to determine whether there are damaged areas (lesions) in your brain. Such lesions indicate a high risk of developing multiple sclerosis. An MRI can also rule out other causes of visual loss, such as a tumour.
• Blood tests. A blood test is available to check for infections or specific antibodies. Neuromyelitis optica is linked to an antibody that causes severe optic neuritis. People with severe optic neuritis may undergo this test to determine whether they’re likely to develop neuromyelitis optica. For atypical cases of optic neuritis, blood may also be tested for MOG antibodies.
• Optical coherence tomography (OCT). This test measures the thickness of the eye’s retinal nerve fibre layer, which is often thinner from optic neuritis.
• Visual field test. This test measures the peripheral vision of each eye to determine if there is any vision loss. Optic neuritis can cause any pattern of visual field loss.