Asymmetries of optokinetic nystagmus in amblyopia: the effect of selected retinal stimulation.

Open loop optokinetic eye movements were measured in response to monocular nasalward and temporalward visual field movement presented at four selected retinal sites in 6 strabismic amblyopes and 4 normal observers. Stimulus sites included the central retina (10 X 10 deg), a large field (40 X 32 deg), a large peripheral field with the center (10 X 10 deg) blocked out and a hemiretinal field (15 X 32 deg) excluding the fovea. We found directional preferences of OKN in amblyopia to nasalward stimulus movement for the foveal and concentric peripheral stimuli. The results of peripheral hemiretinal optokinetic stimulation of amblyopic subjects revealed a deficient OKN slow phase response from the temporal hemiretina, particularly for temporalward stimulus movement. There was no marked asymmetry of OKN in the normal group for the concentric stimuli. A normal preference was found for nasalward and temporalward stimulus field movement imaged on the nasal and temporal hemiretinae respectively. These results are interpreted in terms of a model of cortical and subcortical pathways for OKN derived from comparative studies of cat and monkey.