Optic Neuritis: A Review (Disease/Disorder Overview) (Report‪)‬

Introduction In most parts of the world acute demyelinating optic neuritis (ON) is the most common cause of unilateral painful visual loss in a young adult. In those regions where multiple sclerosis (MS) is common, most cases of ON are related to that disorder, although the diagnosis is not made until a second symptomatic episode (relapse) when the disorder can be referred to as MS-associated ON (MSAON). Typical cases can be referred to as demyelinating ON until a diagnosis of MS is made. Since ON can herald a more diffuse demyelinating disease, care should be taken in making an accurate diagnosis, and careful consideration given to treatment options, particularly as other causes of ON not related to MS require quite different management. The diagnosis of demyelinating ON is usually made clinically, although imaging of the optic nerves, preferably by magnetic resonance imaging (MRI), is mandatory for atypical cases. MRI of the brain can also yield prognostic information in terms of the patient's future risk of a second, MS-defining, episode. Much information has been gleaned from the ON Treatment Trial (ONTT) (1) where 377 patients with acute ON were prospectively assessed with respect to visual function, recurrence of optic neuritis and development of MS over 15 years. (2) The design of the ONTT was to measure visual field and contrast sensitivity as the primary endpoints of the trial and visual acuity and colour vision identified as secondary endpoints. (3) This article reviews adult demyelinating ON as a primary demyelinating inflammation of the nerve occurring either in isolation or in association with MS. ON in childhood, bilateral ON (both excluded from the ONTT) and non-MS-associated ON are important conditions that involve a different set of clinical phenotypes. We refer the reader to recent reviews on the differential diagnosis of ON. (4-6)