The invention provides a method of treating acute demyelinating optic neuritis in a patient suffering therefrom, which method comprises administering a compound to the patient, wherein the compound is phenytoin or an analog or prodrug thereof. The compound acts as a neuroprotectant by partial blocking of voltage-gated sodium channels in axonal other cell membranes thereby reducing the entry of sodium into the respective cell in vivo. The treatment is particularly concerned with preserving vision after onset of the acute demyelinating optic neuritis.