A morphological comparison of foveal development in man and monkey.

The fovea can first be identified in both monkey and human retina at 26-30% gestation as a region containing all adult retinal layers and only cone photoreceptors. A shallow foveal pit and cone outer segments appear by 63-65% gestation in both species. Prenatal development continues rapidly in the monkey, so that by birth a single layer of inner retinal neurons are present in the fovea, cones are three cells deep, inner segments are elongated, and outer segments are up to 50% of inner segment length. In contrast, human fovea does not reach a similar stage until several months after birth. The fovea is adult-like in monkey at 12 weeks and in human at 11-15 months, although human will mature further up to four to five years. This study shows that human fovea is less mature at birth than monkey but develops rapidly in infancy, suggesting that it may be even more susceptible to postnatal environmental influences than the commonly-used monkey model.