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I ANATOMY                

 

II PHYSIOLOGY OF EYE MOVEMENTS  

III CLINICAL EXAMINATION

IV FIXATION INSTABILITY   

VI VESTIBULAR SYSTEM  

 VII CEREBELLAR EYE   MOVEMENTS 

VIII VISUAL FIELDS, PUPIL & THE EYE

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Supranuclear Gaze. Professor A Moodley, NASA Neurology Registrar Weekend, 2019

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The abducens nucleus, located in the pontine tegmentum, contains motor neurons that innervate the ipsilateral lateral rectus and interneurons which decussate in the MLF, and innervate the contralateral medial rectus subnucleus.  Abducens nucleus involvement can be distinguished from abducens nerve injury in that the former produces a gaze palsy to the side of the lesion, whereas the latter produces only a lateral rectus palsy.  Note that this gaze palsy cannot be overcome by oculocephalic or caloric stimulation, as opposed to supranuclear lesions, or lesions of the PPRF.  This suggests that the abducens nucleus is a central integrating final common pathway for horizontal eye movements and that that the vestibular nuclei send excitatory projections to this site.

Involvement of oculomotor control pathways above the level of the abducens nucleus for horizontal eye movements, and above the level of structures for vertical eye movements (cranial nerves III and IV, and the interstitial nucleus of Cajal (INC) in the dorsal midbrain) may produce supranuclear deficits.
Often, such ocular motor disturbances are associated with other neurological deficits, so that the ‘overlap’ of the neurological findings allows location of the level of the lesion in the brainstem region as well as the side. STR 14

Supranuclear ocular motor disturbances usually impair the movement of both eyes, for example, in the form of:

Supranuclear deficits can be distinguished from nuclear insults by the preservation of oculocephalic responses.  Nuclear insults render vestibular ocular reflexes (VOR) dysfunctional, since the final common pathway for vestibular-induced eye movement is controlled by neurons in the respective cranial nerve nuclei and in the INC.