Visual system Eye movement Flashcards
Why do we have eye movements
Necessary for acquiring and tracking visual stimuli
What are movements facilitated by
It is facilitated by the six extraocular muscles in the orbit,
innervated by the three cranial nerves.
(III, IV and VI)
Why are there 6 muscles to facilitate eye movement
so eyeball can rotate, (and go up down left and right)
What is duction
Eye Movement in One Eye
what is simultaneous movement in both eyes in the opposite direction know as
Vergence
What is vergence
what is simultaneous movement in both eyes in the opposite direction
What is convergence
– Simultaneous adduction (inward) movement in both eyes when viewing a near object
For example, in convergence, as part of the near response triad,
both eyes move nasally in order to focus on a near object.
What is Simultaneous adduction (inward) movement in both eyes when viewing a near object
convergence
What is version
Simultaneous movement of both eyes in the same direction
eg
gazing to the right, Dextroversion,
or gazing to the left, Levoversion.
What is Saccade
short fast burst, up to 900°/sec
Can be voluntary or involuntary
What are the different types of saccade
Reflexive saccade to external stimuli
Scanning saccade (eg when reading a book)
Predictive saccade to track objects
Memory-guided saccade (absence of external stimuli)
What is Smooth pursuit
sustained slow movement upto 60°/s
It is an involuntary movement,
driven by a moving target across retina.
What is Smooth pursuit
sustained slow movement upto 60°/s
It is an involuntary movement,
driven by a moving target across retina.
name The Muscles of the Eye (Extraocular muscles)
Six muscles 5 of the 6 muscles come out of a cone from the back of the orbit. The inferior oblique comes in nasally.
Attach eyeball to orbit
Straight and rotary movement
whenever there is contraction of muscle in one eye there is relaxation of the counteracting muscle in the same eye
Four straight muscles
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
2
Superior oblique
Inferior oblique
Where does the superior rectcus attach to the eyeball
Attached to the eye at 12 o’clock
Moves the eye up.
In what direction do the vertical rectus muscles act (superior and inferior rectus)
Pull back wards and nasally
Where does the inferior retcus attach to the eyeball and what is its action
Attached to the eye at 6 o’clock
Moves the eye down.
What is the action of the vertical rectus muscles when the eye is in adducted position
When the eye is in an adducted position,
as shown in the diagram,
the anterior-posterior axis of the eye is not aligned with the vertical rectus muscle action.
Vertical rectus muscles produce torsion motion instead.
What is the action of the vertical rectus muscles when the eye is in adducted position
When the eye is in an abducted position,
the anterior-posterior axis of the eye is aligned with the insertion of the vertical rectus muscles.
In this position,
the Superior Rectus muscle elevates the eye maximally,
and the Inferior Rectus muscle depresses the eye maximally.
In which position does the superior rectus muscle elevate the eye maximally
when eye is in abducted position
In which position does the inferios rectus muscle depress the eye maximally
when eye is in abducted position
Where does the lateral rectus (external rectus) muscle attach
What movement does it cause
Attaches on the temporal side of the eye
Moves the eye toward the outside of the head (toward the temple)
Where does the medial rectus (internal rectus) muscle attach
What movement does it cause
Attached on the nasal side of the eye
Moves the eye toward the middle of the head (toward the nose)
Where does the superior Oblique muscle attach
What movement does it cause
Attached high on the temporal side of the eye.
It originates around orbital apex, Travels through the trochlea
Passes under the Superior Rectus.
Moves the eye in a diagonal pattern down and out
Where does the inferior Oblique muscle attach
What movement does it cause
Attached low on the nasal side of the eye.
Passes over the Inferior Rectus.
Moves the eye in a diagonal pattern - up and out.
Which extraoccular muscles does cranial nerve III supply
Superior rectus
Inferior rectus
Medial rectus
Inferior oblique
Which extraoccular muscles does cranial nerve IV supply
Superior Oblique
Which extraoccular muscles does cranial nerve VI supply
Lateral rectus
Which nerves supply the extra occular muscles
III, IV, VI
How do you test for eye movements
Extraocular Muscle Testing – Isolate muscle to be tested by maximizing its action and minimizing the action of other muscles
How is the lateral rectus muscle tested
Lateral Rectus muscle action is best tested in the abducted position.
How is the medial rectus muscle tested
Medial Rectus muscle action is best tested in the adducted position.
How is the superior rectus muscle tested
Superior Rectus muscle action is best tested in the elevated and abducted position.
How is the inferior rectus muscle tested
Inferior Rectus muscle action is best tested in the depressed and abducted position.
How is the inferior oblique muscle tested
Inferior Oblique is best tested in the elevated and adducted position.
How is the inferior oblique muscle tested
Superior Oblique is best tested in the depressed and adducted position.
Explain eye movements in terms of direction
Up (Elevation)
Supraduction – one eye
Supraversion – both eyes
Down (Depression)
Infraduction – one eye
Infraversion – both eyes
Right – Dextroversion
Right Abduction
Left Adduction
Left – Levoversion
Right Adduction
Left Abduction
Torsion – rotation of eye around the anterior-posterior axis of the eye
What is third nerve palsy
Affected eye down and out
Droopy eyelid (loss of elevator palpebrae superioris)
Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)
What is the reason for the appearance of the eye in third nerve palsy
When there is a complete third nerve palsy,
only muscles not innervated by the third cranial nerve in the affected eye are working.
Namely, lateral rectus muscle, responsible for abduction,
and superior oblique muscle, responsible for depression.
This causes over-action of the two unopposed muscles,
and the affected eye adopts a down and out position.
This is also accompanied by ptosis, or drooping of the eyelid on the affected side,
as the upper lid levator muscle is innervated also by the superior branch of the oculomotor nerve.
What is the reason for the appearance of the eye in third nerve palsy
When there is a complete third nerve palsy,
only muscles not innervated by the third cranial nerve in the affected eye are working.
Namely, lateral rectus muscle, responsible for abduction,
and superior oblique muscle, responsible for depression.
This causes over-action of the two unopposed muscles,
and the affected eye adopts a down and out position.
This is also accompanied by ptosis, or drooping of the eyelid on the affected side,
as the upper lid levator muscle is innervated also by the superior branch of the oculomotor nerve.
What happens in sixth nerve palsy
Affected eye unable to abduct and deviates inwards
Double vision worsen on gazing to the side of the affected eye
What nerve palsies are depicted in the image
What is Nystagmus
Nystagmus refers to oscillatory movement of the eye,
which can be physiological or pathological.
What is optokinetic nystagmus
Opto-kinetic Nystagmus is a form of physiological nystagmus,
triggered by the presentation of a constantly moving grating pattern.
Why does optokinetic nystagmus occur
The eyes track along the grating motion,
with smooth pursuit up to a limit,
and resets the eye position to the centre,
with a burst of fast saccade motion.
This results in cycles of slow phase smooth pursuit,
alternating with fast phase reset saccade in the opposite direction.
