The topography of primate retina: A study of the human, bushbaby, and new‐ and old‐world monkeys

Abstract

The distribution of ganglion cells has been studied in the retinas of four primates: the prosimian bushbaby, the New-World squirrel monkey, the Old-World crab-eating cynamolgous monkey, and the human. The sizes of ganglion cell somas were also measured at a number of retinal locations and compared with similar measurements in the cat retina to test for the presence in primates of retinal specializations such as the visual streak, and for gradients in retinal structure, such as that between temporal and nasal retina. In all four primates, ganglion cell somas in peripheral retina ranged considerably in diameter (6-16 micrometer in the bushbaby, 8-22 micrometer in the squirrel monkey, 8-23 micrometer in the cynamolgous monkey, 8-26 micrometer in the human). It seems likely that the strong physiological correlates of soma size which have been described among cat retinal ganglion cells and among the relay cells of the macaque lateral geniculate nucleus are generally present in primates. In all four primates, evidence was also obtained of a visual streak specialization; the isodensity lines in ganglion cell density maps were horizontally elongated, and small-bodied ganglion cells were relatively more common in the region of the proposed streak than in other areas of peripheral retina. However, the visual streak seems less well developed than in the cat; among the four primate species examined it was best developed in the bushbaby, at least as assessed by the shape of the isodensity lines. All four primates showed a clear foveal specialization, but this feature seemed least developed in the bushbaby. At the fovea, ganglion cells are smaller in soma size than in peripheral retina; they also seemed more uniform in size, although some distinctly larger cells persist in the human and bushbaby. Soma size measurements also provided evidence of a difference between nasal and temporal areas of peripheral retina comparable to that reported for the cat and other species. Thus the primate retinas examined show features, such as the foveal specialization, which seem unique to them among mammals. They also show features, such as nasal-temporal differences in ganglion cell size, and (though weakly developed) a visual streak, which they have in common with other mammals with widely different phylogenetic histories.

Conformal geometry of the retinal nerve fiber layer

“…This suggests an alternate model in which the macular morphogen is spread along a streak-a line segment inside the raphe itself, starting at the macula. This fits with anatomic studies of ganglion cell distribution (19), which demonstrate a (weakly developed) horizontal visual streak in humans.…”

Primate hearing from a mammalian perspective

“…do not have a measure of the width of the field of best vision of squirrel monkeys, we know their fovea is less distinct, consistent with their slightly larger sound-localization threshold (Stone and Johnston, 1981). Localization acuity is not known for any of the strepsirrhines, but it is likely that species such as the Philippine tarsier, galago, and mouse lemur will have progressively poorer soundlocalization acuity, ranging from approximately 9 to 12°, based on the width of their fields of best vision (Stone and Johnston, 1981;Tetreault et al, 2004).…”

“…Localization acuity is not known for any of the strepsirrhines, but it is likely that species such as the Philippine tarsier, galago, and mouse lemur will have progressively poorer soundlocalization acuity, ranging from approximately 9 to 12°, based on the width of their fields of best vision (Stone and Johnston, 1981;Tetreault et al, 2004). The dwarf lemur may have much poorer localization acuity as it is reported to have very little variation of acuity across its retina (Tetreault et al, 2004).…”

Retinotopic Organization and Functional Subdivisions of the Human Lateral Geniculate Nucleus: A High-Resolution Functional Magnetic Resonance Imaging Study

“…Our estimates indicate that the volume of the LGN representing the horizontal meridian is considerably larger than that devoted to the vertical meridian. In human and macaque retinas, the distribution of ganglion cells is significantly anisotropic, elongated along the horizontal meridian into a modest visual streak (Stone and Johnston, 1981;Perry and Cowey, 1985;Curcio and Allen, 1990;. Functionally, peripheral visual acuity is enhanced along the visual streak (Anderson et al, 1992).…”