Optic neuritis is an inflammatory disease of the optic nerve that typically affects young adults. Women are affected more often than men. It is second only to glaucoma as the most common acquired optic nerve disorder in persons younger than age 50.

In this disorder, closely linked to multiple sclerosis, prognosis for visual recovery is generally good. However, return of visual function is almost never complete. After resolution of optic neuritis, virtually all patients show some signs of optic nerve damage, and most are symptomatic. Even when a patient's acuity recovers to 20/20, abnormalities frequently remain in other measures such as contrast sensitivity, color vision, and visual field.

Prior to the Optic Neuritis Treatment Trial (ONTT), well-established guidelines for treating optic neuritis did not exist. Although corticosteroids had been used to treat this disease, studies to demonstrate their effectiveness had not been satisfactory. Some experts advocated treatment with oral prednisone while others recommended no treatment. Anecdotal reports suggested that high-dose intravenous corticosteroids might be effective.

The association between optic neuritis and multiple sclerosis is well established. Optic neuritis may be the first manifestation of multiple sclerosis, or it may occur later in its course. A strong case can be made for "isolated" optic neuritis being a forme fruste of multiple sclerosis, based on similarities between the two in such epidemiologic factors as gender, age, geographic distributions, cerebrospinal fluid changes, histocompatibility data, magnetic resonance imaging (MRI) changes, and family history. The magnitude of the risk of multiple sclerosis after optic neuritis is uncertain. Previous studies have reported very disparate results, with the risk being reported to be as low as 13 percent and as high as 88 percent. The importance of risk factors such as age, gender, and MRI changes in predicting which patients with optic neuritis are most likely to develop multiple sclerosis also is unclear.

The treatment phase of the study was called the Optic Neuritis Treatment Trial (ONTT), whereas the current long-term followup phase is called the Longitudinal Optic Neuritis Study (LONS). The study is being conducted at 15 clinical centers in the United States. Resource centers include a data coordinating center and a visual field reading center.

Patients were randomized to one of the three following treatment groups at 15 clinical centers:

• Oral prednisone (1 mg/kg/day) for 14 days
• Intravenous methylprednisolone (250 mg every 6 hours) for 3 days, followed by oral prednisone (1 mg/kg/day) for 11 days
• Oral placebo for 14 days

Each regimen was followed by a short oral taper. The oral prednisone and placebo groups were double masked, whereas the intravenous methylprednisolone group was single masked.

Baseline testing included blood tests to evaluate for syphilis and systemic lupus erythematosus, a chest x-ray to evaluate for sarcoidosis, and a brain MRI scan to evaluate for changes suggestive of multiple sclerosis.

The rate of visual recovery and the long-term visual outcome were both assessed by measures of visual acuity, contrast sensitivity, color vision, and visual field at baseline, at seven followup visits during the first 6 months, and then yearly. A standardized neurologic examination with an assessment of multiple sclerosis status was made at baseline, after 6 months, and then yearly.