Slow oscillatory eye movement during visual fixation.

A slow oscillatory eye movement was discovered in a 20-min-long recording. The frequency of this slow oscillation was lower than any known eye movement. Fixational eye movements were recorded in seven healthy subjects with four different recording techniques and with different sampling frequencies. The frequency of the oscillation is 0.04-0.10 Hz, and the amplitude is less than 0.2°. Right and left eyes oscillate conjugately in the vertical direction implying a neural control. We suggest the oscillation to be a fourth movement in the fixational eye movement system. The influence of the oscillation on visual function is not known nor the underlying mechanism controlling the eye movement.