Eye coordination Flashcards
Which muscles are innervated by oculomotor
- superior rectus
- medial rectus
- Inferior rectus
- Inferior oblique
- Levator palpebrae superioris (works with superior tasus muscle (aka “muller” which is smooth and sympathetic innervation)
all GSE
How do you test the obliques?
Adduct the eye and go up and down.
Abduct to test the superior and inferior recti.
That is why you go in an H pattern.
What happens to damage to one oculomotor nerve
- Exotropia: ipsilateral deviates “down and out” when patient looks straight ahead. Caused by unopposed actons of lateral rectus muscle.
- Unable to move ipsilateral eye vertically or medially.
- Diplopia- where images don’t overlap properly ontop of each other.
- Mydriasis - no constriction
- loss of accommodation
What is the pretectal nucleus and describe what happens with an oculomotor lesion
Think consensual response - one eye projects to both pretectal nuclei.
Therefore if ipsilateral eye to oculomotor lesion is shown with direct light, it can’t coordinate either eye, so both don’t react.
Normal eye direct light - both constrict
Blind eye direct light - no constriction.
Marcus Gunn pupil
aka Relative afferent pupillary defect
(caused by diabetes or MS, what is the presentation)?
Partial right optic nerve lesion
- diffuse illumination to left eye, causes both to remain dilated
- light on normal eye: both constrict
- Direct light of defective eye: intermediate constriction.
Use the swinging flashlight test because the difference is not as obvious. You will see dilation in response to light.
Left occulomotor nerve lesion,
what happens in dark room, ambient light, direct response in affected, unaffected light.
This one is easy because one eye will stay dilated no matter what you do while the healthy eye responds to changes in light appropriately
Dark room - affected slightly more dilated
ambient light - affected more dilated
direct affected - light in affected eye
sensory info is fine but the efferent limb for left is fked, only normal eye constricts “consensual”
direct normal - still sensation is preserved, efferent is fked.
what is Argyll Robertson Pupil
(lesion unknown) midbrain?
associated with syphillis
diabetes
aka light near dissociation.
Affected pupil will not constrict to light altho normal one will so afferents are intact.
However! Accommodation will have consensual constriction. ??
With partial compression of nerve 3, what is usually the first symptom
The first signs are usually pupillary
This is because the GVE surround the GSE
What is the clinical triad of uncal herniation - transtentorial herniation.
usually caused by supra-tentorial mass
Clinical triad of
- blown pupil -oculomotor nerve
- Hemiplegia - cerebral peduncles.
- Coma - RF - decreased consciousness or coma
Trochlear nerve lesion
Well think about what the trochlear nerve does.
Superior oblique.
(depresses, adducts)
So patient will have
(elevation, abduction)
“extorsion with hypertropia in ipsilateral eye as nerve lesion
**however the nucleus is CONTRALATERAL!
Abducent nucleus can get lesioned by increased ICP, brainstem pushed downwards stretching CN6
Presentation -right CN6 lesion
- Right esotropia when looking straight ahead
- When looking to right - you will get straight looking right eye, this is only because medial rectus weakened
- Left gaze is fine
What are the 6 systems that control eye movement image on the fovea and enable it to stay there (reflexive and voluntary)
- Active fixation - eyes are still and on object of interest
- Saccadic system: extremely fast movement in response to visual targets, tactile stimuli, verbal commands, locations of memory
- Smooth pursuit eye movement: tracks a moving object -(first saccade catches up with object and then you track it)
- Vergence system: for different depths
- Vestibulo-ocular reflexes: holds images during brief head movements
- Optokinetic movements: hold image during translation or sustained rotation.
Eye movements; and nerve firing. Abducens as an example
There are bursts of activity during saccades - saccadic pulses
Position is held by tonic activity because without it the eyes would drift back to center in response to elastic forces
PPRF - paramedian pontine reticular formation
(Horizontal gaze center)
Right PPRF > right conjugate gaze
Left PPRF> left contralateral gaze.
right PPRF projects to
- RIGHT abducens nucleus - right lateral rectus contracts
- Interneuron (travels in MLF) cross and synapses on LEFT oculomotor nucleus to target medial rectus
Right abducens nuclei lesion
- Look straight - right esotropia
- Left gaze fine
- RIGHT GAZE** - just looks straight - lateral rectus doesn’t work, and there is no coordination with left medial rectus
