Counterrolling of the Human Eyes Produced by Head Tilt with Respect to Gravity

Abstract

A photographic method of measuring torsional eye movements (counter-rolling) yielded, on the average, a precision of ±5.3 minutes of arc. Using this method, torsional eye movements compensatory to head (body) tilt were found in all planes tested except the sagittal. In the two intermediate (±45d`) planes the overall counterrolling response was quite similar and somewhat less than that found in the case of lateral tilt. Counterrolling always occurred opposite to the lateral component of head tilt and increased fairly rapidly up to a maximum at a head inclination of between 60d` and 90d`. From this point on counterrolling decreased, but at a lesser rate than it increased, reaching about zero when the head was positioned vertically downward. A difference in absolute amount of torsion of the right eye found between tilting the head (body) leftward and rightward could not be established. However, no difference in counterrolling could be attributed to the order (clockwise or counterclockwise) in which the measurements were made. Variability in counterrolling response was found to be considerable at every position of tilt. A theory attempting to explain the mechanism of otolith organ stimulation is presented.