Definition of Optic neuritis:

Optic neuritis is inflammation of the optic nerve. It may cause sudden, reduced vision in the affected eye.

Causes, incidence, and risk factors:

The cause of optic neuritis is unknown.

Sudden inflammation of the nerve connecting the eye and the brain (optic nerve) can injure the insulation (myelin sheath) surrounding each nerve fiber, causing the nerve to swell.

Causes of the inflammation can include:

• Autoimmune diseases (systemic lupus erythematosus, sarcoidosis, Behcet disease, autoimmune optic neuritis)
• Infections (tuberculosis, syphilis, Lyme disease, meningitis, viral encephalitis, and post-infectious measles, rubella, chickenpox, herpes zoster, mumps, and Mycoplasma pneumonia or other common upper respiratory tract infections)
• Multiple sclerosis (most often in adults, but also in children)
• Toxicity from drugs such as methanol or ethambutol
• Vitamin B-12 deficiency

Risk factors are related to the particular cause.