Visual system- eye movements Flashcards
what is duction?
eye movement in one eye
what is version?
simultaneous movement of both eyes in same direction
right= dextroversion
left= levoversion
what is vergence?
- simultaneous movement of both eyes in opposite direction
what is convergence?
- simultaneous adduction (inward) movement in both eyes when viewing a near target
what is a saccade?
short fast burst of eye movement
can be voluntary or involuntary
what are the types of saccade?
- reflexive saccade to external stimuli (acquiring new external target)
- scanning saccade (reading book)
- predictive saccade to track objects
- memory-guided saccade (in absence of external stimuli)
what is a slow pursuit?
sustained slow eye movement - up to 60deg/sec
driven by motion of moving target across the retina
what are the extraocular muscles?
Where do the extraocular muscles originate?
5/6 from back of orbit
inferior oblique comes nasally
where does the superior rectus attach and what do they do?
attached to eye at 12 o clock
elevates the eye maximally, moves eye up
where does the inferior rectus attach and what does it do?
attached to eye at 6 o clock
depressses eye maximally (moves eye down)
what does the lateral rectus do and where does it attach?
also called external rectus, attaches on temporal side of eye, moves eye towards outside of head (towards temple)
what does the medial rectus do and where does it attach?
also called internal rectus, attaches on nasal side of eye, moves the eye towards the middle of the head (towards the nose)
where is the superior oblique attach and what does it do?
attached high on temporal side of eye
passes under superior rectus
moves eye in a diagonal pattern down and out
travels through trochlea
what does the inferior oblique do and where is it attached?
(faded muscle)- attached low on nasal side of eye and passes over inferior rectus. Moves eye in diagonal pattern (up and out)
what is the innervation of extraocular muscles?
which muscle in involved in looking in each direction?
how is extraocular muscle testing done?
– Isolate muscle to be tested by maximizing its action and minimizing the action of other muscles
what muscle is used for each movement of eye?
- Abduction – Lateral Rectus
- Adduction – Medial Rectus
- Elevated and Abducted – Superior Rectus
- Depressed and Abducted – Inferior Rectus
- Elevated and Adducted – Inferior Oblique
- Depressed and Adducted – Superior Oblique
what is a 3rd nerve palsy?
- Only muscles not innervated by 3rd cranial nerve are working
what are the signs of a 3rd nerve palsy?
- Affected eye down and out
- Droopy eyelid (ptosis) (loss elevator palprebrae superioris- upper lid lavatory muscle innervated by superior branch of oculomotor nerve (3rd))
- Unopposed superior oblique innervated by 4th nerve (down)
- Unopposed lateral rectus action innervated by 6th nerve (out)
what happens in a 6th nerve palsy?
- Affected eye unable to abduct and deviates inwards
- Double vision worsen on gazing to the side of affected eye
what are the causes of 3rd, 4th and 6th nerve palsy?
what is nystagmus?
oscillatory eye movement
what is optokinestic nystagmus?
smooth pursuit + fast phase reset saccade
- Eyes track along grating motion, with smooth pursuit up to a limit and resets eye position to centre with a burst of fast saccade motion
- Results in cycles of slow phase smooth pursuit, alternating with fast phase reset saccade in opposite direction
what is an optokinetic nystagmus reflex useful for?
testing visual acuity in pre-verbal children
by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies
signifies subject has sufficient visual acuity to perceive the grating pattern
