A simple and relatively fast method was used to evaluate visual performance: gratings of sinusoidal luminance profile, generated on the face of an oscilloscope, were reversed in contrast at a rate of 2 Hz. Under these conditions the patients could set separate contrast thresholds for seeing either the structure of a grating or its apparent movement. The grating resolution limit (maximum spatial frequency) for each task was determined by extrapolation from thresholds measured at several spatial frequencies. The resulting ratios of pattern/movement resolution limits (P:M) are usually between 1.6 and 2 for normals and for patients with pathological changes located distally (probably prior to the chiasma). On the other hand in patients suspected of multiple sclerosis the P:M ratios were reduced to below 1.3. It is considered that such results may suggest a central site for the damage, although they do not exclude pre-chiasmal defects which may occur simultaneously during the acute stages of the disease.
Adult Evoked Potentials, Visual