Subjects will be recruited from out-patients assessed for acute demyelinating optic neuritis by neurology, ophthalmology, neuro-ophthalmology at London Health Sciences Center and St. Joseph's Health Care Center in London, Ontario. Subjects will be included only if the first visit takes place within 14 days of symptom onset. Only subjects where the physician who identifies/diagnoses the optic neuritis is considering corticosteroid treatment will be contacted for potential screening and enrollment. To ensure treatment is chosen based on the clinical judgement of physician diagnosing ON, the investigators will only contact potential subjects after the decision to use corticosteroids has been made by the patient's treating physician.