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Role of the central and peripheral retina upon optokinetic nystagmus. Foveal and peripheral nystagmus.

The optokinetic (OK) nystagmus induced by OK stimulus on the foveal area (foveal nystagmus) or on the peripheral retina (peripheral nystagmus) are discussed. Separation of the visual field can be achieved by a combination of a projection type OK stimulator and a masking cylinder driven by a d.c. ENG. Foveal and peripheral nystagmus became increasingly difficult to elicit in tact with narrowing of the visual field or increase in stimulus velocity. The influence of velocity was much more noticeable in the foveal nystagmus. The characteristics of foveal and peripheral OK nystagmus are elucidated by the overlapping method. The foveal nystagmus has a rather distorted form, but its slow-phase eye velocity is the same as the target velocity. It has a tendency to start and reverse with slow phase. Its beating field deviates in the direction of the slow phase. The peripheral nystagmus, on the contrary, has a typical saw-tooth form and its slow-phase eye velocity is slower than the target velocity, even at the low speed stimulus. It has a tendency to start and reverse with the quick phase. Its beating field deviates in the direction of the quick phase.