Monocular and binocular optokinetic nystagmus in humans with defective stereopsis.

In order to investigate the previously suggested relation between cortical binocular function and deficits in monocular optokinetic nystagmus (OKN), monocular and binocular OKN was examined in normal, stereodeficient, and stereoblind observers, using a variety of stimulation velocities and stimulus field sizes. Most stereodeficient and stereoblind observers showed monocular OKN deficits in one or both eyes, which took the form of either a directional asymmetry or a reduction of the response in both directions. The deficits were often more pronounced at higher stimulation velocities and with smaller stimulus field sizes. The severity of the OKN deficit was related to the degree of residual foveal stereopsis, while the type of the deficit seemed to be influenced by the presence and depth of amblyopia. Binocular OKN resembled the best monocular response in subjects with a directional or ocular asymmetry. The results fit well with current animal models of the neural control of OKN.