Binocular immobilization induced by paralysis of the extraocular muscles of one eye: evidence for an interocular proprioceptive mechanism.

1. Spontaneous changes in the positions of both eyes were measured in anesthetized cats before and after infusion of paralytic or anesthetic agents directly into the extraocular muscle capsule behind one eye. 2. Before retrobulbar injection, large changes in eye position were observed in both eyes. The position changes of each eye were independent of each other and often in opposite directions. 3. Application of a paralytic agent into the orbit of one eye reduced the spontaneous position changes in that eye to a very low level. Unexpectedly, the changes in the position of the other, untreated eye were also greatly reduced. 4. Control experiments demonstrated that the binocular immobilization observed after monocular paralysis was not due to 1) leakage of the paralytic agent from the orbit of the treated eye to the orbit of the untreated eye or 2) systemic vascular transport of the paralytic agent. 5. Passive movement of the paralyzed eye did not induce movement of the untreated eye. 6. Application of a local anesthetic agent rather than a paralytic agent to one eye resulted in reversible reduction of movement only in the treated eye, but not in the untreated eye. 7. The results suggest that the reduction of movement in one eye produced by application of a paralytic agent to the other eye is mediated by an afferent neural signal derived from extraocular muscle proprioceptors possibly gated by a central motor control signal.