Synchronous optokinetic nystagmus. The prediction area in normal humans

Optokinetic nystagmus was investigated in 150 normal subjects who were separated into two groups according to age (17-50 years and 65-89 years). The investigations were carried out at target speeds of 10 degrees/sec and 20 degrees/sec. Both of the test situations were within the area of synchronous response, i.e. every target gave rise to one or more nystagmic beats. The normal variation of the eye velocity of horizontal OKN was determined. It was impossible to obtain stable ENG recordings of vertical OKN. No age- or sec dependent asymmetry of the eye velocity was observed. Five of the participants from the older group were unable to produce a continuous and regular OKN. From the rest of the participants regular responses were recorded at one or both of the test situations. The eye velocity is encumbered with a considerable individual variation, which is reduced when considering the difference between clockwise and counter-clockwise OKN.