The Pulfrich spatial frequency phenomenon: a psychophysical method competitive to visual evoked potentials in the diagnosis of multiple sclerosis.

The results of a study in which visual evoked responses (VERs) and a modified Pulfrich method were compared showed that both methods are very effective for the diagnosis of multiple sclerosis. With VERs, 97% of the multiple sclerosis cases were diagnosed correctly, while the corresponding value for the Pulfrich method was 93%. In contrast to VERs, the Pulfrich method allows only measurement of latency differences between the two visual pathways. This method involves measuring the speed required to cause a shift in the apparent depth location of a large, moving, striped pattern observed with a neutral density filter over one eye. A pathological transmission time was inferred when the patients observed a shift in the depth of the moving pattern either without any filter at all or with a filter whose attentuation was no more than 0.2 log units. A further criterion for pathology was a difference of more than 10% between the two eyes in the retinal speed required for a depth displacement using a 1.5 log unit filter. This test requires about 15 minutes, and can be carried out by a technical assistant.