Optic neuritis can involve any portion of the optic nerve and is characterized as an inflammatory, infectious, or demyelinating disorder of the optic nerve. Presenting symptoms typically include loss of visual acuity and visual field changes. Optic neuritis is often a manifestation of multiple sclerosis, but it can also be seen as a component of other disease processes, in particular vasculitis. The characteristic imaging changes of optic neuritis include swelling of the optic nerve and enhancement following the administration of contrast material. Contrast enhanced CT using high resolution mode can show these findings, but the modality of choice is contrast enhanced MRI. It is possible for the optic chiasm to be involved as a part of optic neuritis. If the chiasm is enlarged, however, other diseases known to cause such enlargement (sarcoidosis involving the chiasm and chiasmal neoplasms) should be considered in addition to optic neuritis.