Conservation of absolute foveal area in new world monkeys - A constraint on eye size and conformation

The foveal specializations of five New World monkeys, the marmoset, Callith rix jacchus; the golden-handed tamarin, Saguinus midas niger; the squirrel monkey, Saimiri ustius; the capuchin monkey, Cebus apella; and the howler m onkey, Alouatta caraya were compared. Although retinal area varies by over a factor of two in these monkeys, the area of the fovea does not covary wit h retinal area and remains approximately the same absolute size, as measure d by the dimensions of the high density region of cones, or the rod-free re gion. This constancy in foveal size also holds for rhesus monkeys and human s, bringing the variation in retinal area to a factor of five. Alouatta car aya is unusual, distinguished by a very high central cone density and a sma ll rod-free zone. Physiological constraints that might limit foveal area ov er a wide range of eye sizes are considered. Copyright (C) 2001 S. Karger A G, Basel.