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Neurology aNd Special SeNSeS ` neurology—oPhthAlmology Neurology aNd Special SeNSeS ` neurology—oPhthAlmology SecTioN iii 543

Internuclear Medial longitudinal fasciculus (MLF): pair of MLF in MS.
ophthalmoplegia tracts that allows for crosstalk between CN VI When looking left, the left nucleus of CN VI
and CN III nuclei. Coordinates both eyes to fires, which contracts the left lateral rectus and
move in same horizontal direction. Highly stimulates the contralateral (right) nucleus of
myelinated (must communicate quickly so eyes CN III via the right MLF to contract the right
move at same time). Lesions may be unilateral medial rectus.
or bilateral (latter classically seen in multiple Directional term (eg, right INO, left INO) refers
sclerosis, stroke). to the eye that is unable to adduct.
Lesion in MLF = internuclear ophthalmoplegia INO = Ipsilateral adduction failure, Nystagmus
(INO), a conjugate horizontal gaze palsy. Opposite.
Lack of communication such that when
CN VI nucleus activates ipsilateral lateral
rectus, contralateral CN III nucleus does not
stimulate medial rectus to contract. Abducting
eye displays nystagmus (CN VI overfires to
stimulate CN III). Convergence normal.

Right frontal Right INO (right MLF lesion)
eye field
Voluntary gaze
to left
Left gaze
L R
Lateral Medial
rectus rectus
Impaired adduction Nystagmus
(convergence normal)
CN VI CN III

Oculomotor
Midbrain (III) nucleus

Right MLF
Paramedian pontine
reticular formation (PPRF)
Pons
Abducens
(VI) nucleus

Medulla

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