Pursuit and optokinetic responses in latent/manifest latent nystagmus

Abnormalities of foveal smooth pursuit and the monocular optokinetic response (OKR) have often been reported in subjects with latent nystagmus (LN) and manifest latent nystagmus (MLN). This abnormality typically takes the form of a monocular asymmetry with a deficit in the response to nasal-to-temporal (N-T) motion in the visual field. Previous studies have each presented different interpretations of this finding, depending on whether the characteristics of the spontaneous oscillation were considered when analyzing the measured eye movement response: one report has suggested that these asymmetries are in fact the cause of the spontaneous nystagmus. In this study, pursuit and OKRs were examined separately and, when working synergistically and antagonistically, to attempt to overcome this difficulty. Results suggest that pursuit and the OKR could be symmetric in LN and MLN for both binocular and monocular viewing, which leads to the conclusion that the asymmetric patterns of response often reported in LN/MLN result from either shifts in the zone of minimum-intensity oscillation or from non-stimulus-specific increases in the spontaneous nystagmus.