Visual acuity and ERG-CFF in relation to the morphologic organization of the retina among diurnal and nocturnal primates

Abstract

Visual acuity and ERG critical flicker frequency (CFF) of 4 diurnal and 2 nocturnal primate species were related to the morphologic organization of photoreceptors and the retina. Acuity thresholds of the diurnal squirrel monkey, marmoset, lemur and tree shrew ranged from 0.5 to 1.5′ and of the nocturnal aotus and galago from 3.5 to 8.0′ of visual angle. Species differences in ERG-CFF included high response rates and fast recovery of cone dominated in contrast to duplex or rod dominated eyes. In the temporal retina, there was a trend toward a differentation of an avascular area coinciding with the fovea of the duplex primate eye. Rods, cones and fovea were observed in the squirrel monkey and marmoset. Mostly rods and an area centralis were found in the aotus and galago. Cones were observed predominantly in the tree shrew. The maximum number of ganglion cells was located around the fovea and the area centralis. The electron microscope indicated similarities in ultrastructure of receptor outer segments. Species differences were found in the inner segments and synaptic contacts of photoreceptors. Significant differences were also observed in visual discrimination learning capacity. From the multidisciplinary comparisons it was concluded that similarities in acuity were associated with the convergence of receptors on ganglion cells, whereas visual learning capacity was associated with differences in visual projection and association areas in the brain.