Control of Eye Movements Flashcards
Which eye movements are conjugate? (3)
Which eye movements are disconjugate? (1)
Saccadic
Smooth pursuit
Vestibuloocular
Vergence
Horizontal/vertical systems do what?
Does rapid eye movements that bring the image of an object onto the fovea so the detail can be seen.
Horizontal system tract
- Frontal eye field and superior colliculus synapses in CL PPRF.
- PPRF sends a neuron to nucleus VI (CL now).
- CN VI stays IL to go to LRm. Nucleus VI also sends a fiber to the CL side via MLF to synapse onto nucleus III.
- CN III goes to MRm.
Vertical system tract (simple)
- Frontal eye field and superior colliculus synapses in riMLF.
- riMLF sends fibers to CN IV (SOm.) and CN III (IOm.).
What 3 things contribute to reflex saccadic eye movements?
Supplementary and parietal eye fields.
Superior colliculus.
Burst neurons
Tonic neurons
Pause neurons
Where do these firings occur?
Excitatory firing.
Move eyes toward target.
Inhibit burst neurons to stop further neurons.
Brainstem.
Location of Horizontal movements: burst cells, tonic cells, pause cells.
Burst: PPRF
Tonic: nucleus prepositus hypoglossi (pons)
Pause: Raphe nuclei
Location of Vertical movements: burst cells, tonic cells, pause cells.
Burst: riMLF.
Tonic: interstitial nucleus of Cajal.
Pause: Raphe nuclei
How to test saccadic movements?
Ask pt to visually jump from one object to another.
Destructive lesion defects
Eye deviates toward the lesion.
In seizure activity, the eyes look:
Away from the firing gaze center.
Smooth pursuit purpose
Keeps moving object centered on fovea.
Smooth pursuit tract
- P-O junction goes to pontine nuclei.
- Pontine nuclei to CL vestibulocerebellum.
- Vestibulocerebellum to medial vestibular nuclei.
- Vestibular nuclei send fibers to CL nucleus VI.
- CN VI goes to IL LRm. and fibers to nucleus III (via MLF).
- Nucleus III sends CN III to MRm.
*Can also be done in vertical w/ CN III and IV.
Optokinetic pathway purpose
Holds image of steady target fixed on retina during head movement.
What happens in the optokinetic pathway? (physically, what happens with the eyes?)
Smooth pursuit pathway allows us to remain on target.
Once visual target is broken at limit of visual field, the eyes make a quick move in opposite direction (optokinetic nystagmus).
What MUST be intact for the optokinetic pathway to work?
Parietooccipital eye field
How to test for smooth pursuit movements:
Optokinetic tape. Move tape through the fingers in front of patient.
Lesion of parietal lobe will cause (2):
Loss of smooth pursuit movements toward the side of the lesion.
No optokinetic nystagmus when tape is moved toward damaged lobe.
What does doll’s eye maneuver test?
What is the test?
Tests for vestibuloocular movements.
Have pt stay focused on image and move head quickly.
Explain COWS
Cold water will cause nystagmus (fast phase) toward opposite side.
Hot water will cause nystagmus toward same side.
In a comatose patient, what will the pathology be from doll’s eye maneuver and ice water caloric?
Both reflexes will be absent
Internuclear ophthalmoplegia (INO) defects:
What are the able to do, though?
Where is the lesion?
Weak adduction of affected eye (CN III).
Abduction nystagmus of CL eye.
Convergence.
MLF in pons or midbrain.
What 3 things occur in the near reflex?
Convergence
Accommodation
Pupillary constriction
Argyll-Robertson pupil (neurosyphilis)
Absent light reflex, but pupil constricts in near reflex testing.
Pathway of convergence (overview)
- CN II to LGN.
- LGN to primary visual cortex.
- Primary visual cortex to primary association cortex.
- Primary association nucleus to Edinger Westphal nucleus.
Tumors of pineal gland can cause:
Lesions to the red nucleus can cause:
Pineal - upward gaze palsy
Red nucleus - downward gaze palsy
