Gain of slow-phase velocity of optokinetic nystagmus

Although slow-phase velocity of optokinetic nystagmus (OKN) increases according to the increase of stimulus velocity, it is not obvious whether both are quite equal or not. In this study, gain of slow-phase velocity in OKN response to stimulation velocity was analyzed by two methods of stimulation, constant acceleration, and constant velocity stimulation. In our observation, the gain of slow-phase velocity was not equal to 1.0 even at low-speed stimulation. On the other hand, the number of nystagmus almost corresponded to the number of stimulation stripes passing through the center of an OK-drum up to high-speed stimulation. The results of this study indicate that pursuit eye movement of slow-phase OKN should not be quite equal to that of the eye tracking test, i.e. being required to continuously look at a moving spot.