investigating eye movement systems Flashcards
How many types of eye movement systems are there /?
7 types
What 2 different aims might the types of eye movement have ?
- either fall in Gaze holding- both foveas maintain fixation on the object constantly through time
- Gaze shifting- Both foveas move from one object to another
What is gaze holding example?
if follow bird through sky , you maintain both foveas on that bird at all times
one object to another
What is gaze shifting example?
if you are looking at a book then look at a door
one object to another
How many of the eye movements are gaze holding ?
5 types
How many of the eye movements are gaze shifting?
2 types
What are the gaze holding eye movements ?
Fixational Vestibular ocular- ask px to move head right and left and up and down Optokinetic Smooth pursuit- using ocular motility Vergence- using RAF rule
What are the gaze shifting eye movements ?
saccades - measure using 2 pencils- shifting both foveas to one to the other
fast phase of nystagmus- okmm drone.
What are fixational eye movements ?
- never will measure
- involuntary- make these unconsciously
What is the purpose of fixational eye movements ?
to prevent retinal failing by continuously stimulating g different neurons (TROXLER phenomenon)
-if neurons are stimulated over again - get fatigued - if want to make small eye movements repeatedly over and over again eventually the objects will disappear from your view.
What are the 3 ways fixational eye movement prevent retinal failing ?
micro saccades
drift
tremor
How can we prevent retinal failing?
making tiny eye movements stimulate different receptive fields (at the fovea and macula the receptive field sizes are very small ) and hence are enough to stimulate different neurons and prevent retinal fading- within the macula
Why can we not do retinal fading in the periphery ?
the receptive field sizes re much larger
-therefore these tiny eye movements won’t be able to prevent retinal fading in the periphery
What is vestibular ocular reflex ?
holds images steady as we move around
Head turn to left eyes move to right
What is another e.g for VOR?
spin chair to right - head moves to right- eye moves to the left
What is the stimulus of VOR ?
comes from inner ear- HAIR CELLS
-IF spin px around horizontally in 360 degrees , the horizontal semicircular canal
What happens in VOR transient head rotation ? (acceleration)
-hair cells stimulate the inner ear and send signal for the VOR pathways for eyes to move on the left hand side
What happens in OKN (optokinetic) sustained head rotation (constant velocity)?
when rotation becomes constant the hair cells won’t move anymore, so another eye movement happens.
-becasue the whole scene is is moving, constant world takes by.
What is optokinetic ?
holds images of the world steady on the retina during constant head rotation
- world is steady, keep person spinning- OKN takes over
- keep person steady, spin the whole world- e.g in the train, watching the scene outside- stimulate OKN
What maintains stable retinal image during head movements ?
VOR and OKN
When is it VOR ?
accelerated head movement
When is it OKN?
constant head movement
What are the 2 types of eye moevement in each VOR and OKN?
- if spin in chair to right- eyes would move to left
- the slow phase phase is the eyes move in the direction opposite to the head rotation
-during the fast phase the eye move in the direction of the rotation- e.g spin really fast on the chair.
What is the horizontal pathway for horizontal gaze?
Stimulates right horizontal semicircular canal
Right vesibular nerve
Right medial vestibular nuclear complex
Left VI nerve nucleus (horz. gaze centre).
To right lateral rectus
-6th nerve nucelus sends a signal to the 3rd nerve nucelus via the MLF (medial longitudinal fasciculus)
-Stimulating right Medial rectus & Left lateral rectus (eyes move to the left slow phase).
-sherringtons law- when one muscle contracts the other one relaxes
What is the inhibitory pathway ?
- start off with left medial vestibular nucleus which will cross the midline and send signal to right 6th nerve nucellus (Abucens nucelus) which will send nucleus to right lateral rectus to relax , so right eye can look to left hand side
- the 6th nerve nucelus will also send signal via the MLF to the left 3rd nerve nucelus, which will send a signal to left medial rectus to relax and will make movement to left hand side ( head moves right and eyes move into laevoversion )
Where does the stimulus for VOR come from ?
the inner ear
how do we retain a pure VOR response?
suspend vision
How do we get a pure VOR response in 3 ways ?
via opaque lens
high convex lens
testing in the dark
What is the Dolls head test ?
-clinical examination for VOR
-Rotate head to the right and left.
Rotate head up and down.
If eye movements are equal and opposite to head movement then there is normal VOR.
If patient unconscious can still carry this out.
What is another way you can carry out VOR clinical examination ?
Visual acuity testing during head rotation.
Request patient to read down the chart as you rotate their head horizontally & vertically (2-3 cycles / second)
If patient not able to maintain fixation indicates abnormal VOR (reduced visual acuity).
Reduction of > 2/3 lines indicates a problem
What happens if px has high prescription ?
do this test with CL instead of spectacles
What is the Spinning baby test?
clinical examination for VOR
Hold infant at eye level facing you
Support their face and neck
Examiner rotates 360 degrees
Eyes should move opposite the rotation
Smooth pursuit is unlikely in a young infant
In an older infant they may fixate on examiner face and VOR suppressed
Nystagmus persists for few seconds after rotation
What is a barany chair ?
Can also investigate VOR using this chair.
Head inclined forward 30 degrees from sitting position
What is Caloric testing?
clinical examination for VOR
Tilt patient’s head 60 degrees backward from sitting position.
Add cold water to the ear on one side.
Will induce nystagmus with the fast phase to the opposite side.
Add warm water to the ear on one side.
Will induce nystagmus with the fast phase to the same side.
COWS
cold opposite warm same
What are the 2 movements for OKN/OKR ?
Slow following movement (optokinesis) Corrective saccade (nystagmus)
What do you do to elicit OKN ?
that fully requires movement of the entire visual surround (not common in real life)
How is OKN stimulated in real life ?
it is self motion (sustained head movement at constant velocity) that stimulates OKN.
In the clinic easier to rotate the environment at constant motion rather than the patient
What are clinical examination of OKN ?
Large moving field rotated at constant velocity.
Alternatively, patient rotated at constant velocity.
Small hand held drums occasionally used.
-USING OKN strips or drum
-Subject follows one stripe then rapidly re-fixes on the next stripe.
- Targets should be moved at a minimum speed of 30 degrees/second otherwise smooth pursuit is also tested.
- Investigated horizontally and vertically.
Stripes should be moved from right to left and then from left to right.
Note any difference in response between the two eyes or globe position.
What does smooth pursuit do?
Holds the image of a moving target on the fovea.
How do we test smooth pursuit ?
- Smooth pursuit tested during ocular motility
- Slow following eye movements less than 40 degrees/second
- More accurate assessment Electrophysiological recordings (Electro oculogram)
- Eye tracker
What is vergence ?
-Disjugate movement so that the image of a single object placed simultaneously on both foveas.
What is a Disjugate movement (VERGENCE) ?
= Two eyes move in equal but opposite directions so that the visual axes do not remain parallel.
What vergence can you measure ?
- Horizontally mainly (convergence & divergence)
- Vertical vergence
- Cyclovergence
What does the stimulus convergence come from ?
4 different types
- Fusional vergence (retinal slip)
- Accommodative vergence (blurred image)
- Proximal vergence (awareness of proximity)
- Tonic vergence (tone of medial recti)
Part of the near triad (convergence, accommodation, miosis).
What is the Clinical examination of vergence?
Near point of convergence measure with RAF rule.
Horizontal and vertical vergence tested via motor fusion response to prisms.
Synoptophore can test
Horizontal vertical & cyclovergence.
What are Saccades?
Brings image of object of interest onto the fovea
Short, rapid (400-700 degrees/ second) eye movement
Voluntary
Involuntary (auditory sensory)
When is saccades done?
Re-fixation from one point to another
Scan path’
A series of fixations and saccades used when examining a scene
Vision is suppressed during a saccade
What is voluntary saccades?
-Predictive : know door will open
-Command generated - check your phone
-Memory guided
-Anti-saccades (saccade in opposite
direction of stimulus)
What is involuntary saccades?
Fast phase nystagmus Scan path Reflexive response to auditory clues Somatosensory clues
What is voluntary saccades initiated by ?
frontal cortex
What is involuntary saccades initiated by?
parietal cortex
What is the Horizontal saccadic movement?
Right frontal eye field (voluntary saccade) stimulates left PPRF
left PPRF stimulates left abducens nucleus (VI).
Abducens nucleus contains abducens motor neurones which innervate left lateral rectus.
Abducens nucleus also contains abducens internuclear neurones with axons that project via the contralateral medial longitudinal fasciculus to innervate the contralateral oculomotor nucleus (III).
Oculomotor nucleus contains motor neurones which innervate right medial rectus.
Patient look to the left.
What is the inhibitory pathway for the horizontal saccadic movement ?
listen on the lecture
What is the
Nystagmus quick
phase ?
Reset the eyes during prolonged rotation and direct their gaze towards the oncoming scene.
Vestibular
Optokinetic
What is Nystagmus?
A rhythmical movement of the eyes normally involuntary
Can be normal or abnormal
Nystagmus Fast phase: reset the eyes during prolonged rotation and directs their gaze towards the oncoming scene (after slow phase VOR or OKN).
How do we test for saccades?
Head un-restrained initially
Request the patient to look from one object to another
Observe the movement on one side of the midline and then the other.
Larger saccades tested by asking patient to look at pen on the right and left of the nose.
Assess horizontally and the vertically.
Head restrained then un-restrained to observe the effect.
Accurate examination Electrophysiological recordings (EOG)
