Optic neuritis.

Optic neuritis is an acute inflammation of the optic nerve. It is a common manifestation of multiple sclerosis; it may be the initial expression or occur later in the course of the disease. Approximately 15-20% of cases of definite multiple sclerosis present with optic neuritis; another 40% will suffer an attack at some point. When optic neuritis occurs without antecedent signs of multiple sclerosis, magnetic resonance imaging (MRI) of the brain frequently reveals characteristic signal abnormalities of white matter, and analysis of cerebrospinal fluid often shows oligoclonal bands. Optic neuritis has been considered a forme fruste of multiple sclerosis.