Uniocular and Binocular Scotopic Responsiveness of the Peripheral Retina*

Thresholds were determined with a square test field subtending a visual angle of 0.3° and an exposure time of 0.04 sec, for the right eye, the left eye, and both eyes. The test field was presented at 21 retinal points between 30° to the left and 30° to the right of fixation on the horizontal meridian and on a parallel line 1.5° below the meridian. In the binocular curves the thresholds are high at the center, drop to low levels between 5° and 20°, and then gradually rise farther in the periphery. The monocular curves are asymmetrical due to the blind spot in the left field for the left eye, and in the right field for the right eye. Thresholds measured in the blind spot areas are attributed to excitation of marginal elements by scatter of light in the ocular media. Corresponding to the lack of sensitivity occasioned by the blind spot in one eye is a region of enhanced sensitivity in the other eye as if in compensation. The binocular thresholds are lower than the monocular thresholds, indicating slight binocular summation.