Abstract

In subjects without optic nerve defects, asymmetries in the detection thresholds of equiluminous opponent colors are rare. King-Smith et al.¹ reported four subjects whose detection thresholds violated the symmetry found in normal subjects. Two had acquired retinal defects: one had a microinfarct of the optic nerve, and the other had Leber's optic atrophy; in both cases only the blue-yellow system had an asymmetry. The other two subjects appeared to be normal, but we later discovered that they have mild congenital optic nerve defects. One of these subjects has megalopapilla (abnormally large optic discs), and the other has optic nerve hypoplasia (abnormally small optic discs). The subject with megalopapilla has much higher thresholds for blue than for yellow. The variation of threshold as a function of duration is steeper than Bloch's law predicts for blue but not for yellow. The asymmetry is maximum at approximately 5° parafoveal. The hypoplastic subject was found to have large detection-threshold asymmetries for both red-green and blue-yellow equiluminous spots. Critical durations for equiluminous red were significantly longer than for green, relative to normal subjects. Violations of Bloch's law were also seen for this subject. Spatial and temporal contrast sensitivity for both subjects were within normal limits.

© 1990 Optical Society of America