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

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

3. Extra-Ocular Muscles

4. Infranuclear pathways

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

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

7. 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

9. 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!

10. CN IV Nucleus just caudal and dorsal to III
Innervates Contralateral superior oblique
Exits brainstem dorsally
Longest intracranial course

12. 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?

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

14. 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

15. 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

17. Look for a lesion in:
cerebellum
Pons
midbrain

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

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

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

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

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

26. Supranuclear control

27. Internuclear Pathways
MLF
PPRF

28. 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

30. 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

31. Vertical Gaze
Rostral Interstitial nucleus of the MLF (riMLF) (gaze initiation)
Interstitial Nucleus of Cajal (INC) (gaze holding)
INC
riMLF

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

34. 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.

36. Alternating cover testing
Cover / uncover testing
Quantifying a deviation

37. Name that lesion

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

41. Weber’s Involves Cerebral peduncle Ipsilateral CN III
Contralateral Hemiparesis

45. PPRF lesion Ipsilateral gaze palsy
Provides the supranuclear input to the abducens nuclear complex.
Isolated PPRF lesion will preserve the oculocephalic and caloric reflexes.

47. PPRF & Nuclear sixth Ipsilateral Gaze palsy with
Abnormal oculocephalic and caloric testing

49. 1 and ½ syndrome Lesion of PPRF, CN VI nucleus, MLF
Ipsilateral gaze palsy with
ipsilateral INO

50. Remember
Know the anatomy and you know the lesion.