[Does proprioception of the extrinsic eye muscles participate in equilibrium, vision and oculomotor action?]

Extrinsic eye muscles respond to both proprioceptive and visual impulses. Histology of ocular proprioceptive receptors shows them to be qualitatively and original, neuromuscular bundles are found in primates, and so called "palisade sensory nerve endings" in felines. Golgi's osteotendinous receptors are apparently absent. The number of muscle receptors is high and their proportion in relation to muscle weight even more so. The afferent pathway for this sensory system initially accompanies the motor fibers of oculomotor III, IV, ans VI nerves. Some fibers continue with these nerves to the brain stem while others join the ophthalmic branch of the trigeminal nerve (probably in the cavernous sinus). Cell bodies of proprioceptive fibers are located either in the mesencephalic root of the trigeminal nerve and in the Gasserian ganglion. The superior colliculus, center of eye-head coordination integration, also receives proprioceptive data. Proprioceptive afferent signals also project on two cerebellar cortex regions, one in the VI th and VII th lobules of the posterior lobe vermis, the other in the flocculus, all major centers for control and interaction of visuocervicovestibular activity. Extraocular proprioceptive impulses play an important role as do visual influx, in the maturation of the visual cortex in mammalia. Moreover, maintenance of binocular integration appears to require both coherent binocular vision and balanced bilateral, extraocular afferent impulses. Clinical consequences are multiple. Proprioceptive imbalance due to oculomotor dysfunction could explain the attendant visual deficit, which is reversible after correction of they motor disorder. Forced excentration of gaze provokes equilibrium disturbances in normal subjects. In cases of oculomotor palsy, the accompanying vertigo often observed could thus be due à lack of coordination between the intention of movement and its execution. Many oculomotor signs are dependent on the position of gaze alone, in the absence of any visual guide: end-position nystagmus gaze nystagmus, rebound nystagmus, gaze drift, periodic alternating and vertical superior nystagmus, ocular flutter and opsoclonus, nystagmus retractorius, etc. Proprioceptive impulses from extrinsic eye muscles are probably necessary for assessment of orbital coordinates of the ocular globe position during target fixation: this emphasizes the importance of this proprioceptive factor in the origin of ocular jerks. Proprioceptive impulses may play a crucial role in the triggering of the rapid phase of nystagmus, thus conditioning the variations in amplitude seen in provoked nystagmus tests.