This proposal is to continue a long-term follow-up study of the cohort of patients who were entered into the Optic Neuritis Treatment Trial (ONTT) between 1988 and 1991 and have been followed as part of the Longitudinal Optic Neuritis Study (LONS) since 1992. The ONTT's primary objective was to assess the efficacy of corticosteroids in the treatment of acute optic neuritis. The LONS' primary objectives are (1) the evaluation of the long-term course of visual function after optic neuritis and (2) investigation of the relationship between optic neuritis and multiple sclerosis (MS). This application is for a continuation of the LONS to acquire additional valuable long-term follow-up information about both the visual course and the neurologic course in this unique patient cohort. The LONS provides a unique opportunity to study a cohort of well- characterized patients with optic neuritis. No other study has ever assembled and evaluated so extensively with standardized methodology such a large number of patients with optic neuritis. The importance of the treatment trial in providing a cohort of patients which could be followed longitudinally to answer many key visual and neurologic questions concerning optic neuritis was recognized from the onset of development of the ONTT protocol. This cohort of patients was assembled through considerable effort and cost. The costs involved in the current proposed five-year extension are small compared to the overall study costs. The information emanating from this study will have both therapeutic and quality of life relevance for patients with optic neuritis. For the first four years of the proposal, patient contact will be maintained through phone calls and mailings from the Data Coordinating Center. In the fifth year, the 14 LONS clinics will be recertified and each patient will be seen for an ocular examination, visual function testing, and neurologic examination by protocols currently utilized in the LONS. This visit will coincide with 15-17 years of follow up for each patient. Major manuscripts are planned for both the ophthalmic and neurologic results. More than 80% of the original cohort remains in follow up and mechanisms are in place to assure that this high rate will continue so as to provide valid results for the long-term study.