Abstract

Cataract and poor refraction cause reduction of visual acuity and of sensitivity to luminance contrast. However, a blurred retinal image effects the visibility of a suprathreshold chromatic contrast much less than the same suprathreshold luminance contrast.¹ The advantage of color is even more marked at threshold. A retinal blur, which reduced visual acuity from normal to between 0.1–0.05, increased luminance thresholds for large stationary targets (greater than 2–3°) and coarse gratings by a factor of 5–10, while causing only minor changes in the thresholds for detecting isoluminant gratings consisting of chromatic and white bars. The dependency of a blur-to-normal sensitivity ratio on spatial frequency is presented for luminance gratings and equiluminous chromatic/achromatic gratings. These results, and accompanying temporal dependencies, demonstrate clear differences in the physiological processing of chrominance and luminance. This was confirmed in an electrophysiological experiment where +5 diopter blur reduced the response of primate retinal M_α-cells to luminance contrast significantly, whereas the response of P_β-cells to chrominance contrast was virtually unaffected.

© 1991 Optical Society of America