Anatomy of eye movements Flashcards
What muscles control torsion when eye is abducted?
Obliques
What muscles control torsion when eye is adducted?
Rectus
Third nerve palsy resting gaze
Down (IV) and out (VI), with ptosis and nonreactive to light.
What can cause III nerve palsy
PCOM aneurysm, uncal herniation
Right trochlear nucleus innervates?
Left superior oblique.
IVth nerve palsy
Eye is up and in.
Abducens nerve palsy
One eye can’t look laterally, one eye deviated inwards
Draw the pathway of lateral gaze and conjugate gaze in the other eye.
PPRF tells ipsilateral abducens nucleus to fire, abducens nucleus tells ipsilateral VI nerve to fire, and sends a projection via the CONTRALATERAL MLF to contralateral III nucleus, which tells contralateral eye to look medially.
Lesions of abducens nerve
CN VI palsy, no abduction of ipsilateral eye
Lesion of abducens nucleus or PPRF
Neither eye can look to affected side because abducens nucleus knocked out, so ipsilateral eye cannot abduct, and contralateral eye cannot adduct.
Lesion of MLF
Ipsilateral eye cannot adduct, but contralateral eye can abduct.
INO
One eye cannot adduct, but the other can abduct. This is an MLF lesion.
Parts of brain that initiate eye movements
Frontal and parietal cortical eye fields, send projections to subcortical regions (SC, pretectum, reticular formation).
Saccades and pathway for horizontal and vertical
Fast conjugate eye movements. Cortical eye fields, superior colliculus, PPRF and riMLF (rostral interstitial nucleus of MLF in midbrain, vertical).
PPRF projects to ipsilateral 6 nuc
riMLF projects to ipsilateral 3 to control up down movements.
Smooth pursuit
Dependent on a cortico-ponto-cerebellar network.
Nystagmus
Named for fast phase (under midbrain control). There’s also a smooth pursuit phase (under pontine/cerebellar control).
Vestibular Ocular Reflex, pathway of turning head to right
Mediated by a 3 neuron arc. Activates right horizontal canal and inhibits left horizontal canal, causes conjugate gaze to left. Activated vestibular nerve fibers project to medial vestibular nucleus. MVN excites contralateral 6 nuclei, which projects to ipsilateral rectus muscle and to contralateral medial rectus via MLF. Simultaneously, MVN inhibits ipsilateral abducens. This relaxes ipsilateral lateral rectus and relaxes the contralateral medial rectus.
Caloric testing
Cold = opposite, warm = same.
So, cold in right ear = nystagmus fast phase to the left because the body thinks the head is turning to the left.
Hot in right ear = nystagmus to the right because body thinks head is turning to the right, so it sends eyes left, eyes will try to correct by turning right quickly.
Fast phase commanded by?
Cortex
Slow phase commanded by
Gaze centers.
Vergence eye movements
Complicated, but disconjugated.
Vergence
accomodation
miosis.
One and a half syndrome
Neither eye can look right (abducens nucleus lesion), right eye cant adduct either (lesion in MLF).
