neurologic disorders
Conjugate Gaze Palsies
Horizontal gaze palsies
Conjugate horizontal gaze is controlled by neural input from the cerebral hemispheres, cerebellum, vestibular nuclei, and neck. Neural input from these sites converges at the horizontal gaze center (paramedian pontine reticular formation) and is integrated into a final command to the adjacent 6th cranial nerve (abducens) nucleus. The 6th cranial nucleus controls the lateral rectus on the same side and projects to the contralateral 3rd cranial nerve nucleus via the medial longitudinal fasciculus (MLF) to activate the medial rectus. Inhibitory signals to opposing eye muscles occur simultaneously. The most common and devastating impairment of horizontal gaze results from pontine lesions that affect the horizontal gaze center and the 6th cranial nerve nucleus. Ischemic Stroke are a common cause, resulting in loss of horizontal gaze ipsilateral to the lesion. In palsies due to stroke, the eyes may not move in response to any stimulus (eg, voluntary or vestibular). Milder palsies may cause only nystagmus or inability to maintain fixation. Another common cause is a lesion in the contralateral cerebral hemisphere rostral to the precentral gyrus (called the frontal eye fields). These lesions are typically caused by a stroke. The resulting palsy usually abates with time. Horizontal conjugate gaze mediated by brain stem reflexes (eg, in response to cold-water caloric stimulation) is preserved. 