Eye movement Flashcards
Muscles
Any movement up or down involves >= 2 muscles!
Adduct/converge = medial rectus - elevate = inferior oblique - depress = superior oblique Abduct/diverge = lateral rectus - elevate = superior rectus - depress = inferior rectus
Direct
- elevate = inferior oblique + superior rectus
- depress = superior oblique + inferior rectus
Cranial nerves
All run through cavernous sinus, near internal carotid
Tonic activity -> inc or decrease for movement, new positions
Oculomotor (3)
- midbrain ventral to periaqueductal grey -> interpeduncular fossa (near post cerebral and communicating arteries) -> all ipsi except LR, SO, also levator palpebrae
- carries PNS from Edinger-Westphal -> ciliary ganglion -> pupil constrict and ciliary/lens
Trochlear (4)
- trochlear nucleus -> decussates -> ponto-mesencephalic junction -> cavernous sinus -> contralateral SO
- long and skinny -> traumatic damage
Abducens (6)
- abducens nucleus (facial colliculus) -> ponto-medullary junction -> ipsi LR
PNS eye control
lens accom, constrict (accom, converg, light)
Light reflex:
Optic nerve -> tract -> pre-tectal nuclei ->
Edinger-Westphal nucleus (bilateral) ->
outside of oculomotor (CN III) - susceptible to compression ->
ciliary ganglion -> sphincter pupillae (bilateral)
Can have isolated loss of light constriction with preserved accom, converge (ex pre-tectal or peripheral syphilis, DM)
Saccadic movement
Sudden “saccades” - no vision during movement (blurs)
- new object or catch up with sudden change (ex face features)
- must be accurate -> 200 ms lag to plan, check movement
- head follows in 20-30 ms -> compensation via vestibulo-ocular
Generation - frontal eye cortex, superior colliculus
- vertical via rostral interstitial nucleus
- horizontal via PPRF -> CN VI -> MLF -> CNIII
vs microsaccades - use neighboring retina cells to avoid adaptation
Conjugate horizontal gaze
ex eyes to L visual field
R frontal eye field cortex -> R superior colliculus ->
L (contralateral) PPRF -> L ipsilateral abducens
- L lateral rectus
- MLF -> contralateral R oculomotor -> R medial rectus
Key locations
- frontal eye center = premotor cortex -> movement away from active side
- PPRF - para-median pontine reticular formation -> movement towards active side
Eye palsies
Loss of function -> drift away from that movement
- > double vision (worse in weak position, bad eye is “further from center”)
- > turn head to bring in line
CN III
- abducted, inadequate vertical
CN IV - extorts, medial
- tilt head away from bad eye (other eye intorts to compensate)
CN VI - adducted
- spin head towards bad eye
Superior colliculus
Input: - retina (visual) -> superficial layers - inferior colliculus (auditory) - spinal cord (proprioception, somatic) - cortex Maps stimuli Output -> from deep layers - PPRF, midbrain reticular formation, spinal cord (tectospinal) -> reflex eye and head movements
MLF
Medial longitudinal fasciculus
Input from vestibular, PPRF, CN III, CN IV, CN VI nuclei
- ex connects CN VI and contralateral CN III -> horizontal
(lesion -> internuclear ophthalmoplegia - lateral not followed by other eye)
PPRF
Paramedian pontine reticular formation
At level of facial colliculus, CN IV bisects
Critical for voluntary horizontal movements
- damage -> can’t look toward injured side
Multiple neurons type -> burst and tonic activity
Voluntary vertical gaze
Diffuse cortical areas -> rostral interstitial nucleus (midbrain) ->
- > posterior commissure (dorsal midbrain)
- > b/l CN III, CN IV
Damage (RIN or post commissure)
-> loss of voluntary but can still move with vestibular
Intact with pontine damage (ex “locked-in”)
Smooth tracking
Only if “locked” onto object
Shares vestibulo-ocular pathways
Occipital eye field = visual association area (locks in) ->
(frontal eye field ->) ipsilateral pontine nucleus (NOT PPRF) ->
middle peduncle -> contralateral flocculus -> inf peduncle ->
vestibular nucleus -> bilateral PPRF, CN VI -> MLF -> CN III, CN IV
Reflexes use same pathway!
Fixation - fixate on moving target
Optokinetic - involuntary fixation on moving target (relative to head…?) - ie looking out of moving car
- track -> saccade towards new object (optokinetic nystagmus)
- lost when object moving towards cortical lesion
Vestibulo-ocular reflex
Vestibular nerve -> (nucleus ->) flocculus -> vestibular nucleus ->
- bilateral PPRF, CN VI -> MLF -> CN III, CN IV
Damage to tract - drift (as if head were moving) -> saccadic (nystagmus)
Loss of cortical input -> static drift without saccadic
Vergence
Less well-understood:
- requires occipital lobe -> mesencephalic reticular
- probably superior colliculus
Coordinated movement, constriction, ciliary muscles
Nystagmus
Pendular - equal phases, not CNS or vestibular
Jerk - normal at edges of visual field
- vestibular system (inner ear, CN VIII, nucleus, flocculus, MLF)
- can also be from drugs, toxins
- slow phase - vestibulo-ocular reflex
- fast phase - compensatory from cortex
- named for fast component
SNS eye control
Hypothal -> descending -> thoracic -> cerv ganglion -> int carotid ->
- Pupil dilation
- Lev palpebrae + Muller’s muscles -> opening
Cilio-spinal reflex:
- noxious -> thoracic -> peripheral chain -> active dilation
- does not use central SNS pathways - can be preserved
Horner’s syndrome:
- miosis, ptosis
- anhydrosis - location by innervation (ex only forehead = int carotid, lat face = sup cerv gang, face + neck = cerv chain, arm/body = thoracic)
