The abducens nucleus, located in the pontine tegmentum, contains two populations of motor neurons¹:

1. Those that innervate the ipsilateral lateral rectus.
2. Interneurons which decussate in the MLF, and innervate the contralateral medial rectus subnucleus. 

The abducens nucleus is the final common motor pathway for horizontal conjugate eye movements, as it receives input for horizontal saccades, VOR, and smooth pursuit².

Lesions of the abducencs nucleus result in²:

• Ipsilesional horizontal gaze palsy. Acutely, there is an associated contralesional gaze deviation.
• Loss of all conjugate movements (saccades,pursuit,VOR) toward the side of the lesion.
• Sparing of vertical movements and vergence.  Vergence is spared because vergence commands are sent directly to medial rectus motoneurons in the oculomotor nucleus,without passing through the abducens nucleus or the MLF.
• Horizontal gaze-evoked nystagmus is present on looking away from the lesion.

Abducens nucleus involvement can be distinguished from abducens nerve injury in that when the nucleus is damaged, this will result in a gaze palsy to the side of the lesion, whereas damage to the 6th nerve fasciculus 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.

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