To the Editor. —In reading Beck's 1 editorial on the optic neuritis treatment trial, it seems that magnetic resonance imaging (MRI) is only being used to predict future development of multiple sclerosis. New evidence raises the possibility that MRI may be useful in a primary diagnostic role. Miller et al 2 recently reported on a series of 44 eyes with optic neuritis. They showed that MRI was useful in identifying the site of inflammation of the optic nerve in 84%. Thirty-four percent showed inflammation in the intracanalicular portion of the nerve. In analyzing the visual outcome by site of inflammation, Miller et al found that those with an intracanalicular site of inflammation showed poorer or slower recovery compared with those with inflammation at other sites (73% vs 50% or less). They postulated a logical reason for this result: Edema in the enclosed space of the canal was causing optic nerve