Luminance-onset, pattern-onset and pattern-reversal evoked potentials in human albinos demonstrating visual system anomalies.

Most fish, amphibians, reptiles and birds have laterally placed eyes and primarily panoramic vision. These vertebrates usually have complete crossing of optic fibres at the chiasm, i.e., optic ganglion fibres originating from each eye terminate in visual centres of the contralateral hemisphere. One of the features of the mammalian visual system is the appearance of an uncrossed optic projection terminating in visual centres of the ipsilateral hemisphere. As the eyes shift to a more frontal position on the head the number of ganglion fibres originating in temporal retinae increases. Concomitantly, stereoscopic vision and binocular overlap of visual fields increase. The number of optic fibres that do not cross at the chiasm varies: approximately l-5 percent in guinea pigs and mice, 5-10 percent in rats, 20 percent in dogs and horses, 30-40 percent in domestic cats, 4030 percent in primates (Giolli. and Creel, 1973; Hayhow et al, 1960; Polyak, 1957).