Meridional variations of the scotopic sensitivity in the human retina

The absolute threshold of the dark-adapted retina for a 1 degree circular white light stimulus located at 15 degrees eccentric to the fovea was measured on four meridians. In each of the 11 tested subjects the sensitivity was found to be higher on the 90 degrees suprafoveal vertical meridian, on average by 0.3 log nLa compared to the subfoveal vertical meridian. On the two oblique 45 degrees and 135 degrees meridians of the upper retina the sensitivity was only very slightly lower compared to the 90 degrees meridian.