Acute retrobulbar neuritis is a disease of the optic nerve, chiasm or tract usually characterized by marked and sudden loss of sight in one or both eyes, with a central or paracentral scotoma. Rarely the fields are contracted. Occasionally there is pain on movement of the eye. The pupil often shows hippus. The fundus may be normal, or there may be venous congestion, optic neuritis or papilledema of as much as 6 D. When the lesion is close to the globe the changes in the disk are pronounced and the condition is called optic neuritis. When the lesion is behind the entrance of the retinal vessels into the optic nerve the fundus is usually normal and the condition is called retrobulbar neuritis. Although the two conditions are treated as separate and distinct diseases in the textbooks, the differences between acute optic and acute retrobulbar neuritis are quantitative rather than qualitative