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I ANATOMY                

 

II PHYSIOLOGY OF        EYE MOVEMENTS  

III EXAMINATION: EYE MOVEMENTS & NYSTAGMUS 

IV FIXATION INSTABILITY   

VI VESTIBULAR SYSTEM  

 VII CEREBELLAR EYE   MOVEMENTS 

VIII CN PALSIES, VISUAL FIELDS, PUPIL & THE EYE

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Lesions affecting the cortical connections to the nuclei of cranial nerves 3, 4 and 6, are termed supranuclear

Lesions affecting the connections between nuclei are internuclear

Lesions affecting the nerves, neuromuscular junction, or muscles are infranuclear1.

Video 1. Supranuclear Gaze. Professor A Moodley, NASA Neurology Registrar Weekend, 2019

 

(vv)SNGaze.mp4(tt)

The abducens nucleus, located in the pontine tegmentum, contains motor neurons that innervate the ipsilateral lateral rectus, as well as 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, which receives excitatory projections from the vestibular nuclei2.

Supranuclear deficits arise from 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).

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.

 

 

References
  1. Glisson CC. Approach to Diplopia [published correction appears in Continuum (Minneap Minn). 2020 Feb;26(1):240]. Continuum (Minneap Minn). 2019;25(5):1362-1375. doi:10.1212/CON.0000000000000786
  2. Strupp M, Kremmyda O, Adamczyk C, et al. Central ocular motor disorders, including gaze palsy and nystagmus. J Neurol. 2014;261 Suppl 2:S542-58