Changes in compensatory eye movements after unilateral labyrinthectomy in the rabbit.

Compensatory (slow phase) eye movements elicited by sinusoidal oscillation on a torsion swing were measured in rabbits, 6 months after destruction of the left labyrinth. A range of combinations of stimulus frequencies (0.048-1.8 Hz) and amplitudes (1-25 degrees) were used. Gain (amplitude of cumulative slow phase eye movement/amplitude of swing), phase (eye position vs. swing position - 180 degrees) and directional asymmetry were calculated from averaged records. With eyes covered, gain was much less than half of normal and phase lead was increased by at least 20 degrees. Spontaneous drift was minimal or absent; a slight asymmetry of reactions (preponderance of smooth movements to the intact side) was found. In the presence of vision, reactions were slightly improved, but only for low stimulus velocities. It is concluded that although the acute effects of unilateral labyrinthectomy in rabbits subside and a static equilibrium is achieved, dynamic performance of vestibular reactions remains much below normal.