Analysis of Retinal Function by a Two-Filter Method

Abstract

Any two colored lights are effective in some characteristic energy ratio for stimulating cones, and some other characteristic ratio for stimulating rods, owing to the different spectral sensitivities of these receptors. Such ratios can be used to assess precisely the contributions of rods and cones to visual responses. In these experiments a violet and a yellow test light are used in this way to analyze cone and rod participation in dark adaption, and in the thresholds of the dark-adapted retina at various distances from the fixation point (“retinal profiles”). Also, since the human macular pigment absorbs the violet light and not the yellow, these lights can map the extent and depth of the yellow patch. A functional cross section of the retina results, measuring separately rod and cone activities and macular pigmentation, that agrees reasonably well with histological descriptions. A considerable section of dark adaptation is shown to involve mixed cone and rod responses. Thresholds of the dark adapted eye near the foveal border are similarly mixed, Color sensations at the threshold desaturate with the first participation of rods, and are wholly lost while cone activity is still prominent. The macular pigmentation becomes appreciable at some distance from the fixation point, and in this subject increases regularly in depth to a maximum in the central fovea.