Nystagmus Responses in a Group of Normal Humans during Earth-horizontal Axis Rotation

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Abstract
Horizontal eye movement responses to earth-horizontal yaw axis rotation were evaluated in 50 normal human subjects who were uniformly distributed in age (20-69 years) and equally divided by gender for each decade. The subjects were rotated with eyes open in the dark, using clockwise and counterclockwise 607s velocity trapezoids. The nystagmus slow component velocity (SCV) was analysed using four parameters: Amp, Bias, Mod and Tau. Amp and Tau characterize the canal-ocular reflex to constant velocity steps, while Mod and Bias characterize the “AC” and “DC” components of the otolith-ocular reflex. Results indicated that intersubject variability was larger than that seen in earth-vertical axis data. Tau depended significantly (p<0.05) upon subject gender, while Mod increased monotonically with age decade. Linear regression showed a positive correlation between pairs of SCV magnitude parameters (Amp, Bias and Mod), suggesting a common scaling effect. In addition, there was a negative correlation between the value of the decay time constant Tau and each of the three magnitude parameters. Thus, despite large intersubject variability, parameters that describe earth-horizontal yaw axis responses are loosely interrelated and some of them vary significantly with gender and age.