Visual Neuroanatomy
Efferent Pathways
Vivek Patel, MD
University of Ottawa Eye Institute
Neuro-Ophthalmology
Visual Neuroanatomy
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Afferent – eye to
brain
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Pupillary reflex arc
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Efferents – eye
movements
Extra-Ocular Muscles
Infranuclear pathways
CN III
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Innervates Levator,
inferior oblique &
all recti except
lateral rectus
Projects ventrally
Enters cavernous
sinus after crossing
PCOM
CN III Injuries
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Categorized by age
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Children
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Congenital
AVM
Tumor
Young Adults
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Demyelination
Vascular
Tumor
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Older Adults
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Vascular
Tumor
CN III Subnuclei
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All subnuclei are ipsilateral EXCEPT
Levator subnucleus forms a fused
central nucleus
Superior rectus subnuclei decussate to
innervate contralateral superior rectus
muscle
IS it nuclear or peripheral ?
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It must be nuclear if
Bilateral CN III without ptosis
Unilateral CN III with bilateral ptosis
BUT
Complete bilateral CN III
Bilateral ptosis
May be either!
CN IV
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Nucleus just caudal and dorsal to III
Innervates Contralateral superior oblique
Exits brainstem dorsally
Longest intracranial course
CN IV injuries
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Intrinsic
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Trauma
Tumor
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Medulloblastoma
Ependymoma
Metastatic
Demyelination
Vascular
Congenital ( high vertical vergence amplitudes and
objective excyclotorsion only)
Bilateral: V-pattern esotropia and excyclotorsion greater
than 15 degrees.
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Resultant compensatory head position?
CN IV injuries
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Extrinsic
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Tumor
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Pinealoma
Metastatic
Hydrocephalus / Aqueductal stenosis
Skew Deviation?
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Supranuclear cause of vertical
misalignment
Does not necessarily obey the 3-step
test
Ipsilateral intorsion (not extorsion as in
IV palsy)
Interruption of otolith-ocular pathway at
some point along it’s course
Skew deviation - OTR
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Vestibulo-cerebellar:
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Ipsilateral head tilt
Ipsilateral hypotropia
Excyclo of hypo eye, incyclo of hyper eye
Midbrain:
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Contralateral head tilt
Ipsilateral hypertropia
Excylo of hypo eye, incyclo of hyper eye
Look for a lesion in:
1) cerebellum
2) Pons
3) midbrain
Normal counter-roll
R IV palsy
Ocular tilt rxn (skew)
CN VI
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Innervates ipsilateral lateral rectus
Interneurons to contralateral medial
rectus via MLF
Runs near:
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CN VII
MLF and PPRF
Vestibular Nuclei
Peduncle
CN VI
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Origin: ponto-medullary junction
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Projects ventrally along clivus
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Tethered at apex of the petrous bone by
petroclinoid ligament
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Enters Cavernous sinus
CN VI Injuries
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Vascular
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Anterior inferior cerebellar or paramedian
perforators
Demyelination
Trauma
Tumor
Cavernous Sinus
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Site of multiple
cranial nerve
palsies
Vascular
Tumor
Idiopathic
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Tolosa-Hunt
Supranuclear control
Internuclear Pathways
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MLF
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PPRF
Paramedian Pontine Reticular
Formation
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Horizontal Gaze center
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Initiates horizontal eye movements
Bilateral, within Pons
Projects to ipsilateral CN VI nucleus
Lesions of the PPRF cause ipsilateral
gaze palsies
PPRF lesions do not affect
oculocephalic & caloric reflexes
MLF
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Midbrain to cervical spine
Composed of interneurons – ipsilateral
CN VI to contralateral CN III.
fascicle for horizontal gaze and vertical
gaze that connects the VI and III
nuclear complexes.
Trochlear nerve and otolith ocular
pathways also use the MLF
Vertical Gaze
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Rostral Interstitial nucleus of the MLF (riMLF)
(gaze initiation)
Interstitial Nucleus of Cajal (INC) (gaze holding)
INC
riMLF
Upgaze
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Lateral riMLF projects to contralateral
inferior oblique and superior rectus
sub-nuclei
Remember Superior Rectus fascicle
decussates
Downgaze
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Medial riMLF projects downward to
ipsilateral superior oblique and inferior
rectus sub nuclei
Remember the CN IV fascicle
decussates
Vertical gaze is initiated by Bilateral
activation of the riMLF and INC.
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Alternating cover testing
Cover / uncover testing
Quantifying a deviation
Benedikt’s
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Involves Red Nucleus
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Ipsilateral CN III
Contralateral involuntary movements
Weber’s
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Involves Cerebral peduncle
Ipsilateral CN III
Contralateral Hemiparesis
PPRF lesion
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Ipsilateral gaze palsy
Provides the supranuclear input to the
abducens nuclear complex.
Isolated PPRF lesion will preserve the
oculocephalic and caloric reflexes.
PPRF & Nuclear sixth
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Ipsilateral Gaze palsy with
Abnormal oculocephalic and caloric
testing
1 and ½ syndrome
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Lesion of PPRF, CN VI nucleus, MLF
Ipsilateral gaze palsy with
ipsilateral INO