neurologic disorders
Conjugate Gaze Palsies
Vertical gaze palsies
Upward and downward gaze depends on input from fiber pathways that ascend from the vestibular system through the MLF on both sides to the 3rd and 4th cranial nerve nuclei, the interstitial nucleus of Cajal, and the rostral interstitial nucleus of the MLF. A separate system descends, presumably from the cerebral hemispheres, through the midbrain pretectum to the 3rd and 4th cranial nerve nuclei. The rostral interstitial nucleus of the MLF integrates the neural input into a final command for vertical gaze, similar to the horizontal gaze center for horizontal gaze. Vertical gaze becomes more limited with aging. Vertical gaze palsies commonly result from midbrain lesions, usually infarcts and tumors. In upward vertical gaze palsies, the pupils may be dilated, and vertical nystagmus occurs during upward gaze. Parinaud syndrome(dorsal midbrain syndrome), a conjugate upward vertical gaze palsy, may result from a pineal tumor that compresses the midbrain or, less commonly, a tumor or infarct of the midbrain pretectum. Parinaud syndrome is characterized by Impaired upward gaze Lid retraction (Collier sign) Downward gaze preference (setting-sun sign) Convergence-retraction nystagmus Dilated pupils (about 6 mm) that respond poorly to light but better to accommodation (light-near dissociation) 