Visual Neuroanatomy Efferent Pathways Vivek Patel, MD University of Ottawa Eye Institute Neuro-Ophthalmology

Visual Neuroanatomy Afferent – eye to brain Pupillary reflex arc Efferents – eye movements

Extra-Ocular Muscles

Infranuclear pathways

CN III Innervates Levator, inferior oblique & all recti except lateral rectus Projects ventrally Enters cavernous sinus after crossing PCOM

CN III Injuries Categorized by age Older Adults Children Young Adults Congenital AVM Tumor Young Adults Demyelination Vascular Older Adults Vascular Tumor

CN III Subnuclei 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 ? 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 Nucleus just caudal and dorsal to III Innervates Contralateral superior oblique Exits brainstem dorsally Longest intracranial course

CN IV injuries Intrinsic Trauma Tumor Demyelination Vascular Medulloblastoma Ependymoma Metastatic Demyelination Vascular Congenital ( high vertical vergence amplitudes and objective excyclotorsion only) Bilateral: V-pattern esotropia and excyclotorsion greater than 15 degrees. Resultant compensatory head position?

CN IV injuries Extrinsic Tumor Hydrocephalus / Aqueductal stenosis Pinealoma Metastatic Hydrocephalus / Aqueductal stenosis

Skew Deviation? 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 Vestibulo-cerebellar: Midbrain: Ipsilateral head tilt Ipsilateral hypotropia Excyclo of hypo eye, incyclo of hyper eye Midbrain: Contralateral head tilt Ipsilateral hypertropia Excylo of hypo eye, incyclo of hyper eye

Look for a lesion in: cerebellum Pons midbrain

Normal counter-roll R IV palsy Ocular tilt rxn (skew)

CN VI Innervates ipsilateral lateral rectus Interneurons to contralateral medial rectus via MLF Runs near: CN VII MLF and PPRF Vestibular Nuclei Peduncle

CN VI Origin: ponto-medullary junction Projects ventrally along clivus Tethered at apex of the petrous bone by petroclinoid ligament Enters Cavernous sinus

CN VI Injuries Vascular Demyelination Trauma Tumor Anterior inferior cerebellar or paramedian perforators Demyelination Trauma Tumor

Cavernous Sinus Site of multiple cranial nerve palsies Vascular Tumor Idiopathic Tolosa-Hunt

Supranuclear control

Internuclear Pathways MLF PPRF

Paramedian Pontine Reticular Formation Horizontal Gaze center 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 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 Rostral Interstitial nucleus of the MLF (riMLF) (gaze initiation) Interstitial Nucleus of Cajal (INC) (gaze holding) INC riMLF

Upgaze Lateral riMLF projects to contralateral inferior oblique and superior rectus sub-nuclei Remember Superior Rectus fascicle decussates

Downgaze 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.

Alternating cover testing Cover / uncover testing Quantifying a deviation

Name that lesion

Benedikt’s Involves Red Nucleus Ipsilateral CN III Contralateral involuntary movements

Weber’s Involves Cerebral peduncle Ipsilateral CN III Contralateral Hemiparesis

PPRF lesion 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 Ipsilateral Gaze palsy with Abnormal oculocephalic and caloric testing

1 and ½ syndrome Lesion of PPRF, CN VI nucleus, MLF Ipsilateral gaze palsy with ipsilateral INO

Remember Know the anatomy and you know the lesion.