In order to understand the vision of patients with long standing optic neuritis, contrast perception was analysed in some detail for three patients with uniocular anomalies. Contrast detection and contrast matching experiments each demonstrate anomalies in contrast processing for eyes with optic neuritis. In this regard, optic neuritis differs from all other visual anomalies so far investigated where the suprathreshold deficits (from matching experiments) are slight compared with those measured under threshold conditions (from detection experiments). Contrast discrimination is also impaired to a mild degree in optic neuritis but this cannot be predicted on the basis of the matching results. These results bear upon the currently proposed models for contrast coding in the normal visual system as well as the nature of the underlying pathology in optic neuritis.