Mysterious Sparing of Blue Sensitivity on Yellow Backgrounds in Dominant Optic Atrophy

Abstract

We have previously described several optic atrophy patients whose deficits in psychophysical responses have been interpreted as a selective loss of tonic ganglion cells. The patients’ responses to flicker (e.g. deLange curve) are normal, however, their spectral sensitivities for a 1°, 1 Hz, foveal test flash on a 10° white background do not show the three normal peaks (440, 520 and 600 nm, conducted through tonic cells?) but instead have been replaced by a single peak at 555 nm corresponding to phasic cell responses as described by De Monasterio (1978) and others. Detection of a test spot on blue, magenta or yellow backgrounds produces responses whose characteristics are similar to those of photoreceptors (cones). In 9 of 13 patients we have interpreted as having a selective loss of tonic ganglion cells, the response to a blue test flash on a 10° yellow background was reduced as much as 2.5 log units (corresponding to their large spectral sensitivity losses on a white background and very poor FM 100-hue scores). In 4 of the 13 patients, though performance in detecting the 1° test flash on a white background was depressed (> 1 log unit), sensitivity was closer to normal for the detection of a blue test spot on a yellow background. It previously has been assumed that blue cones contribute exclusively to color-opponent channels. Observation of the above four cases leads one to question the generality of this statement. Theories which may account for this phenomenon in relation to post-receptoral processing are discussed.