Development of the optokinetic system in macaque monkeys.

Optokinetic nystagmus in response to horizontal movement of a whole field random dot pattern was measured in infant macaque monkeys from the first week to about 5 months after birth using electrooculography. During monocular and binocular viewing conditions stimulus velocities were varied between 10 and 120 degrees/s. Monocular stimulation in the temporonasal direction yielded slow phase gain of the optokinetic system which was relatively constant for a given stimulus velocity over the whole period of observation. Gain during nasotemporal stimulation was also clearly present but significantly lower at early stages and increased during further development. This asymmetry of monocular horizontal optokinetic nystagmus (OKN) clearly depended on the stimulus velocity. At lower stimulus velocities (10-20 degrees/s) OKN was largely symmetrical at 2-5 weeks of age. At higher stimulus velocities (40 degrees/s) symmetry was reached at about 12 weeks of age or even much later (80-120 degrees/s).