Physio-anatomy of ocular motility

1. Ocular Motility
Basic Sciences
YONG MENG HSIEN 2021

3. Q
• Anatomy/Physiology of
– efferent visual system
– supranuclear or infranuclear efferent visual system
– cranial nerves for ocular movements
– Orbital apex, SOF, cavernous sinus
– EOM
• Specific functions of eye movement
– horizontal and vertical gaze
– saccade, pursuit, VOR, optokinetic
– laws in ocular motility
• Pathogenesis/Pathology
– gaze palsy: INO, one and half
– myasthenia gravis

4. Q (true/false)
1. Eye movements are not controlled by cortical
function
2. Posterior commissure projecting axons from INC to
contralateral ocular motor nuclei
3. Smooth pursuit system does not decussate
4. Smooth pursuit system is a ipsilateral system
5. Oblique muscles insert at posterior-lateral aspect
of the globe
6. Origin of all EOMs are AOZ
7. Insertion of EOMs/spiral of Tillaux
8. EOMs receive innervation from outer surface

5. Q (true/false)
1. Superficial/dorsal part of superior colliculus
processes motor signal (deep/ventral part)
2. Dorsolateral pontine nuclei are neurons for vertical
saccade (smooth pursuit)
3. Brodmann area 8 controls pursuit eye movement
(saccade)
4. MLF receives projections from ipsilateral superior
vestibular nucleus (contralateral medial vestibular
nucleus)
5. Ipsilateral vestibular system provides tonic input
for vertical gaze (contralateral for horizontal)

6. Outline
• Terminology & Laws
• Anatomy
– supranuclear & infranuclear
• Physiology and Control
– supranuclear & infranuclear

8. Monocular Eye Movement
• = Ductions
• Agonist
• Synergist
• Antagonist
• Sherrington law

9. Binocular Eye Movement
• = Versions or Vergences
• Yoke muscles
• Herring law

10. Binocular Eye Movement
2x basic movements:
1. gaze shift
2. gaze stabilization/holding
6x functional systems or classes:
1. visual fixation
2. vestibular ocular reflex/VOR
3. optokinetic
4. smooth pursuit
5. saccades
6. vergence

12. Donder & Listing Laws
•Donder Law
–For any one gaze direction, the line of sight belong to
the definite orientation of vertical horizontal retinal
meridian
–Relative to the coordinate of the space
–The eye always assume the same unique orientation
in 3D
–Torsion is constrained
•Listing Law
–All movements from primary position are true to the
meridian
–Occurs without torsion
–With respect to the primary position
–True for movement around vertical and horizontal
axes in the equatorial plane

14. Ocular Movement- Anatomy
Supranuclear
• Cerebral cortex
– FEF, MT/MST/POT
– + subcortex: basal ganglia (BG), superior colliculus (SC) and
thalamus
• Brainstem
– Neural networks & premotor neurons
– Reticular formation- mesencephalic/para-
pontine/medullary
– + neural integrators
– + tracts (MLF, PC)
• Vestibulo-cerebellum system

15. Ocular Movement- Anatomy
Infranuclear
• Ocular motor CN (III, IV, and VI)- nuclei & nerve
• NMJ
• EOMs

18. Supranuclear control- Cortex
Initiation of movement
– frontal lobe (FEF/Brodmann 8 & SEF)
– saccade (memory-guided and volitional)
– parietal lobe (posterior parietal cortex)
– saccade (visually reflexive)
– temporal lobe (POT or MT/MST)
– smooth pursuit

19. Supranuclear control- Subcortex
Processing, relaying, filtering
– Basal ganglia
– caudate nucleus, putamen nucleus, and substantia nigra
– Thalamus
– internal medullary lamina and pulvinar
– Brainstem to cortex
– Superior colliculus
– deeper layers: stratum griseum profundum and stratum
album profundum
– Internal capsule

21. Supranuclear Control- Brainstem
- Neuronal generator/network
• Midbrain (mesencephalic reticular formation, MRF)
– vertical & torsional gaze
• Pons (paramedian pontine reticular formation, PPRF)
– horizontal gaze
• Medulla (medullary reticular formation, MedRF)
– horizontal gaze (inhibit)

22. Brainstem Control (Neuron)
Midbrain
• rostral interstitial nucleus of MLF (riMLF)- vertical & torsional gaze/saccade (excitatory
burst neuron)
• interstitial nucleus of Cajal (INC): vertical & torsional gaze/saccade (inhibitory burst
neuron)
• region of riMLF and INC: vertical & torsional saccades (inhibitory burst neuron)
• y-group cells: vertical smooth pursuit and vertical vestibular eye movements
Pons
• nucleus raphe interpositus (RIP): omnipause cells
• nucleus reticularis tegmenti pontis (NRTP): long-lead burst cells
• dorsolateral pontine nuclei (DLPN): neurons for smooth pursuit
Medulla
• nucleus prepositus hypoglossi (NPH): neural integrator for horizontal gaze/eccentric gaze

23. Brainstem Control (Tracts)
• Medial longitudinal fasciculus (MLF)
• major pathway for relaying signals
• contralateral PPRF/6th CN nuclei to ipsilateral 3rd CN nuclei
(horizontal)
• vestibular system to gaze center/CN nuclei (vertical &
horizontal)
• Posterior commissure (PC): INC to contralateral CNs
III/IV/VI/INC (vertical)
• Cell groups of paramedian tracts (PMTs): neurons that project
from the CN VI nucleus to the cerebellum

24. Supranuclear control-
Vestibular & Cerebellum
• Cerebellum
• Filtering, relaying, processing
• Vermis, floculonodular lobe (paraflocculus and dorsal
vermis), brachium conjunctivum
• Vestibular (pons/medulla)
• VOR, eye positioning during head movement/tonic input
• Vestibular nuclei
• semicircular canal: rotator head mvm (angular)
detection
• utricle & saccule: head tilt (linear)

27. CN III, IV, VI: Anatomy
• Functions
• Nuclei
• Connections
• Course & relationships
– fasciculus
– basilar (subarachnoid)
– Cavernous sinus
– Intraorbital/EOM
• Clinical relevance

29. EOM- the Anatomy
• Embryo: mesoderm
– 5W start (primordium) → 2yr completed migration of
insertion (Tillaux)
• Functions (1/2/3)
• Macroscopic (table)
– origin/course/insertion/size
– blood supply/innervation
• Microscopic:
– characteristic (nerve-fiber ratio, fatigue resistant, fast)
– fibers (types, inner global vs outer orbital layer)
– Content of fiber cell & surrounding

31. Six cardinal position
(right eye)

33. EOM- Actions
• EOM= 2x horizontal rectus & 2x vertical rectus & 2x oblique
• Horizontal rectus (MR & LR)
– only horizontal actions (adduction or abduction)
• Vertical rectus (SR/IR)
– primary vertical actions (elevation/depression)
– forms a 23° angle relative to the visual axis in the primary
position
– greatest elevation with the eye in the abducted position
– secondary torsion & tertiary adduction.
• Oblique muscles (SO/IO)
– primary torsional actions (intorsion or extorsion)
– forms a 51° angle relative to the visual axis in the primary
position
– leads to secondary vertical actions (depression/elevation best
when the eye is adducted) & tertiary abduction.

35. Saccade
• Def: fovea shifting to eccentric target/bring object in peripheral to fovea
• Character:
– Ballistic (cannot altered once initiated)
– V= >100/400 degree per sec (depends on amplitude of mvm)
– L= 100-200msec
– Duration < 1msec
– Supplement pursuit >50degree/sec (cogwheel pursuit)
– Fast phase of nystagmus/OKN
– Saccadic suppression/omission to avoid blurring
• Anatomy:
– FEF/SEF (volitional pathway/voluntary)
– Parietal lobe (visual reflexive pathway/involuntary)
– Subcortex: SC/BG/thalamus (signal processing)
– Decussate at midbrain
– Contralateral gaze center/PPRF
– Neural integrator (riMLF/INC for vertical gaze, NRTP/RIP/NPH for horizontal)
• Clinical:
– Latency/accuracy/velocity/conjugacy
– Hypo/hypermetric

36. Pursuit
• Def: fovea/fixation holding on moving object
• Characters:
– Smooth slow
– V= < 100 degree per sec (30-40)
– L =125-150 msec
– Cogwheel if V>50 degree/sec (pursuit fall behind → saccade to re-fixate
→ pursuit again)
• Anatomy:
– MT/MST/POT junction
– Subcortex: int capsule/BG/SC (signal processing)
– Vestibulocerebellum (signal processing)
– Ipsilateral gaze centre/PPRF (double decussate at pons & cerebellum)
• Clinical:
– slow component of OKN nystagmus (unilateral lesion = asymmetrical =
Cogan’s law)
– Latency/accuracy/gain (1-0, lag behind stimulus & catch up with
saccade)

37. Vestibulo-ocular reflex (VOR)
• Def: hold image/fwd fixation at brief head mvm
• Supplement pursuit with brief/high frequency head movement
• Characters:
– Involuntary/non optical reflex
– Slow 20-50 degree/sec
– Extreme short latency 10 msec (fast reflex)
• Anatomy
– Semicircular canal (endolymph mvm/velocity changes) & utricle/saccule
(otoliths/linear acceleration/gravity)
– Vestibular nerve (CN VIII) → nuclei @ rostral pons-medulla
– Modified by cerebellum
– Cross over to contralateral gaze center/PPRF
• Clinical
– Brainstem test
• doll eye reflex/oculocephalic reflex
• caloric test with COWS nystagmus)
– By pass supranuclear input above PPRF

38. Optokinetic
• Def: hold image on retina on sustain eye movement
• Supplement pursuit/vestibular reflex
• Characters:
– physiology nystagmus
– Biphasic (slow pursuit/quick saccade)
– Velocity 30-100 degree per sec
– Latency 70 msec
• Anatomy
– Slow pursuit (direction of OKN)- by ipsilateral MT/MST/POT
– Fast saccade (opposite)- by ipsilateral FEF
• Clinical
– VA test
– Functional blindness
– Congenital nystagmus with paradoxical OKN reflex
– Assess homonymous hemianopia (impaired OKN when turn to opposite
hemianopic field/ipsilateral to lesion- of parietal/temporal)
– Detect INO (toward eye with adduction failure)
– Detect Parinaud convergence retraction nystagmua (rotate OKN downward)
– Detect vascular occipital lesion (symmetrical OKN)

39. Vergence
• Def: eyes move in opposite direction for BSV
(disconjugate binocular mvm)
• by relative movement toward or away from the eyes
• Character:
– Slow 20-50 degree per sec
– Latency 160 msec
• Anatomy
– Pretectal nucleus → CN III nuclei (EW & MR nucleus) & VI
nuclei
• Clinical
– Spared in solely MLF/posterior midbrain lesions
– Light-near dissociation (parinaud/Adie/Argyll Robertson)

40. Fixation mvm/Troxler’s
phenomenon/microsaccadic refixation
• Def: small eye mvm to move retinal image at
regular interval, or correction of ocular drift
(prevent image fade/bleaching of
PRC/attenuated neural response)
• 0.1-0.2 degree of visual angle, square waves,
slight pause 200ms (intersaccadic interval)