Optic neuritis (ON) is an inflammatory demyelinating condition of the central nervous system that results in the loss of vision and is associated with eye pain, loss of color vision and visual field deficits. While ON can occur in isolation, it is often part of Multiple Sclerosis (MS), Acute Disseminated Encephalomyelitis (ADEM) or Neuromyelitis Optica Spectrum Disorder (NMOSD). ON can be the presenting feature of MS (15-20% of the time) and occurs in 50% percent of those diagnosed with MS at some point during their illness. ON is typically monocular (affecting one eye), though it can also affect both eyes sequentially or simultaneously. Bilateral ON tends to be more common in children younger than 15 years old.
The most common cause of ON is inflammatory demyelination of the optic nerve. The pathology (similar to that of acute MS) involves plaques in the brain, with perivascular cuffing, edema in the myelinated nerve sheaths, and myelin breakdown. Similar to MS, a genetic susceptibility for ON is suspected, and it is believed that the demyelination in ON is immune-mediated. However, the specific mechanism and target antigen(s) are unknown.