Control of Eye Movement Flashcards
Primary gaze
Neutral position
Lateral eye moveent
Adduction
Abduction
Intorsion
Upper eye approaches nose
Extorsion
Upper eye approaches temporal region
How many muscles are involved for eye movement above or below the horizontal plane
Two muscle
Muscle in upward gaze
Superior rectus
Inferior oblique
Muscle in downward gaze
Inferior rectus
Superior oblique
Cranial Nerves Involved
CN III - Occulomotor Nerve
CN IV - Trochlear Nerve
CN VI - Abducens Nerve
CN III: Motor Nerve Fibers
Occulomotor nucleus → levator muscles (all except lateral rectus)
CN III: Parasympathetics
Edinger-Westphal Nucleus → Cillary Ganglion → Constrictor pupilae & ciliary muscle
CN III: Where is the Edinger-Westphal Nucleus located
In the midline between both occulomotor nuclei
CN III: What is the role of the parasympathetic
Round the lens for close focus
CNIII Describe the pupillary light reflex
Afferet nerve fibres → Pretectal nuclei → EWN → cilliary Ganglion → Sphincter pupillae muscle → constrict pupil
CN III: Third Nerve Palsy: 3 signs
Ptosis
Diliated pupil
Pupil looks lateral because lateral rectus is innervated by CN VI
CN IV: Function
General somatic efferent innervation to superior oblique
CN IV: Pathway
CN IV Nucleus → decussation → Exit dorsal brainstem → Cavernous sinus (lateral wall) → Superior oblique muscle
CN IV: Damage
- Extorsion + medial deviation
- Inability to depress eye
- Assume abnormal head position to try and allign the good & bad eye
Easily damaged in head trauma
CN IV
CN VI: Function
General soatic efferent innervation to lateral rectus
CN VI: Pathway
CN VI Nucleus (caudal pons) → Exits pontomedullary junction → cavernous sinus (crosses internal carotid) → lateral rectus
Tonic activity?
Yes, extraoccular motor neurons
Define saccade movements
Voluntary rapid eye movements to allow eyes to keep up with a moving target (3 seconds) followed by head movement
Define microsaccades
Small movements that prevent an image from remaining on the same rods & cones (if not, you would lose vision through adaptation)
Pathway for saccades for horizontal eye movement
- Cerebral cortex or Superior colliculus
2. Paramerdian pontine reticular formation (PPRF)
Pathway for saccades for vertical eyemovement
- Cerebral cortext or superior colliculs
2. Rostral Interstial Nucleus
Supperior Colliculus
Function
Afferent
Efferent
Saccadic movements
Afferents: Retina, inferior colliculus, spinal cord
Efferent: Spinal cord → Tectospinal tract
Brain stem → Tectoeticular tract
How is the superior colliculus organized what is superficial and what is deep?
Visual input is superficial and Motor input is deep
What is opthamoplegia?
Damage to to the MLF transfering information from PPRF to CN VI and CN III nuclei
When do Smooth Persuit Movements occur?
Eyes move smoothly when tacking objects or when head is moving
What pathway is involved in Smooth Pursuit Movement
Vestibulo-ocular Reflex (VOR)
What does damage to the VOR cause?
Drift in eyes as if head was moving → triggers saccadic eye movements to keep eye in focus → Nystagmus
Fixation Reflex
Fixate on moving target (Smooth persuit pathway)
Optokinetc Reflex
Involuntary fixation on objects that are moving relative to the head
Convergence or Divergence Reflex
Convergence accompanied by pupilary constriction to allow focus on close objects
Pupillary Light Reflex
Constriction in respose to light
Pendular nystagmus
Oscillations are equal in both directions
Not CNS or vestibular damage
Jerk nystagmus
Rapid and slow compent
Slow: Imbalance in vestibular system, flocculos or MLF
Rapid: Compenstatory to try and remain fixated on the object
When is it normal to have nystagmus?
End of range of eye movement
