visual systems 4 Flashcards
what is eye movement?
Voluntary or involuntary of movement of eyes
Necessary for acquiring and tracking visual stimuli
Facilitated by the six extraocular muscles (recti and obliques)
innervated by the three cranial nerves (III, IV and VI)
what are the different types of eye movements?
Duction – Eye Movement in One Eye
Version – Simultaneous movement of both eyes in the same direction
Vergence – Simultaneous movement of both eyes in the opposite direction
Convergence – Simultaneous adduction (inward) movement in both eyes when viewing a near object
what are the speeds of eye movement?
Saccade – short fast burst, up to 900°/sec: Reflexive saccade to external stimuli Scanning saccade Predictive saccade to track objects Memory-guided saccade
Smooth Pursuit – sustain slow movement up to 60°/s:
Driven by motion of a moving target across the retina.
what are the 6 extraoccular muscles?
attach eyeball to socket
straight and rotary movement
superior rectus inferior rectus lateral rectus medial rectus superior oblique inferior oblique
what does each of the extraocular muscles do?
superior rectus:
attaches at 12 oclock
moves the eye up
inferior rectus:
attaches at 6 oclock
moves the eye down
lateral rectus:
attached to temporal side
moves the eye sideways towards the outside of the head
medial rectus:
attached to nasal side
moves the eye towards the nose
superior oblique: attached high on the temporal side passes under superior rectus moves the eye down and out travels through the trochlea
inferior oblique:
attached low in the nasal side
passes over the inferior rectus
moves the eye up and out
what nerves innervate the extraocular muscles?
oculomotor (III):
superior branch -
superior rectus
levator palpebrae superioris
inferior branch- inferior rectus medial rectus inferior oblique parasympathetic nerve (constricts pupil)
trochlear (IV):
superior oblique
abducens (VI):
lateral rectus
how is eye movement testing done?
Extraocular Muscle Testing – Isolate muscle to be tested by maximizing its action and minimizing the action of other muscles
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 are the directions of eye movement?
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 sixth nerve palsy?
Affected eye unable to abduct and deviates inwards
Double vision worsen on gazing to the side of the affected eye
what is Optokinetic Nystagmus Reflex?
Nystagmus – Oscillatory eye movement
Optokinetic Nystagmus = Smooth Pursuit + Fast Phase Reset Saccade
Optokinetic Nystagmus Reflex is useful in testing visual acuity in pre-verbal children by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies
Presence of Optokinetic Nystagmus in response to moving grating signifies that the subject has sufficient visual acuity to perceive the grating pattern
