THE EFFECT OF GRAVITY ON THE RESTING POSITION OF THE CATS EYE

We measured rotation (horizontal, vertical and torsional) and translat ion (horizontal and vertical) of the paralysed cat's eye in response t o 45-degrees steps of orientation presented in a pseudorandom order ar ound the roll and pitch axes (with respect to the horizontal canals). During changes of position of the animal in the roll plane, the eyes r otated towards the lowest part of the orbit (left with left ear down; top when the cat was upside down, etc.) by an average of 0.55-degrees. Changing orientation in the pitch plane evoked vertical rotations of +/- 1.42-degrees (upwards eye movement during forwards head pitch) and torsional rotations of +/- 1.3-degrees. All these rotations taken tog ether suggest that the centre of mass is in front of, below and tempor al to the centre of rotation. The eyes translated temporally (thus sep arating by 0.72 mm) during forward pitching and there was a small vert ical displacement (0.23 mm) when the animal was upside down. These fin dings are discussed with respect to a possible role of the extraocular proprioception system.