Impaired temporal resolution of vision after acute retrobulbar neuritis.

Following retrobulbar neuritis patients need a greater interval between two flashes of light in order to see them as double. The abnormality is large and easily detectable; the values lie well outside the normal 99 per cent tolerance limits. The abnormality sometimes occurs in localized retinal areas but can cover the whole visual field. The abnormality is a persistent one, remaining up to five years after visual acuity has returned to normal. It can occur in the absence of optic atrophy and with normal visual fields. There is also a delay in visual perception following retrobulbar neuritis but when this and double flash discrimination are both measured at the same retinal sites, the areas of abnormality do not correlate for the two tests. This indicates that the two tests monitor different aspects of visual damage. Double flash threshold can be a more sensitive indication of visual damage due to demyelination than conventional clinical tests including critical flicker fusion frequency. It provides an absolute measurement of local damage in the visual field and has advantages over the recording of perceptual delay and of evoked potentials.