Causes

The exact cause of optic neuritis is unknown. It's believed to develop when the immune system mistakenly targets the substance covering your optic nerve, resulting in inflammation and damage to the myelin.

Normally, the myelin helps electrical impulses travel quickly from the eye to the brain, where they're converted into visual information. Optic neuritis disrupts this process, affecting vision.

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 fibers 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, 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.