The diagnosis of Optic Neuritis is based on the patient’s medical history, as well as the absence of other diseases which can cause visual loss. The eye exam may help in showing abnormalities at the back of the eye in the optic disc, which is the part of the optic nerve visible using an instrument called an ophthalmoscope. There may be abnormalities of visual field testing, colour vision, testing, and visual acuity testing that aid in the diagnosis.
Occasionally, other diseases have to be considered in diagnosing Optic Neuritis, but these are usually apparent during the history and examination. For example, some people who are older than 50 experience a sudden loss of vision in one eye which is due to a problem with blood flow to the eye, and not due to inflammation.