Abstract

A century has passed since it was first reported that an observer's anomaloscope setting (Rayleigh match) can be affected by field size, with less red light required for smaller fields. This phenomenon, known as the color-match area effect, appears to be due to longer cone outer segments in the foveola than in the parafovea, which results in higher effective optical density of foveolar cone photopigments. Since Rayleigh match midpoints are determined by ratio of quantal catches in the cone outer segments for the different wavelengths, they will not be affected by reduced numbers of cones, changes in the gain of the cone signals, or postreceptoral processing (these other factors may affect match width, but not midpoint). Therefore, the color-match area effect can be used as a noninvasive measure of the integrity of foveal architecture¹ (i.e., the normal increase in cone outer segment length from parafovea to foveola and normal outer segment alignment). A reduced or absent color-match area effect would reflect abnormal foveal architecture, including a relative decrease in the length of the foveolar cone outer segments or a tilting of the plane of the photoreceptors.

© 1993 Optical Society of America