Flicker fusion in multiple sclerosis.

This paper is concerned with a study of thresholds of critical flicker fusion frequency (C.F.F.) of a light stimulus in patients suffering from multiple sclerosis. The capacity of normal human vision to appreciate the intermittency of rapidly repeated light stimuli is a function of great physiological interest, and it may be impaired by disease at many sites in the visual pathway. Thus Parsons and Miller (1957) examined cases of multiple sclerosis on the hypothesis that general damage within the central nervous system might be responsible for depressing critical flicker fusion frequency. However, they found the C.F.F. so frequently impaired in their group that they were forced to conclude that retrobulbar neuritis must play a part in damaging its perceptual mechanism. They noted a correlation with pallor of the discs but did not observe cases during the course of retrobulbar neuritis. They suggested the potential value of C.F.F. estimation as a diagnostic test. These observations showed such a striking difference between cases of multiple sclerosis and controls that it appeared profitable to validate them for estimations made with different apparatus, and if possible to confirm their conclusion that depression of C.F.F. was related to the occurrence of retrobulbar neuritis. The relation between C.F.F. and visual acuity and the visual fields in multiple sclerosis is also of considerable interest. Kurachi and Yonemura (1956) investigated four cases of retrobulbar neuritis and demonstrated the slower rate at which the flickering light was fused subjectively. Most of the work on flicker fusion has been carried out by ophthalmologists but psychiatrists have also taken an interest in the subject in relation to its impairment in organic psychosis. Phillips (1933) and Riddell (1936) have studied the visual fields by means of flicker from the point of view of the neurosurgeon and this work made it clear that C.F.F. might be depressed by lesions far removed from the retina and