eye movement Flashcards
why do we move our eyes? (3)
brings points of interest over the fovea
gives high level of visual acuity
to foveate
to stop blurring
describe fast eye movement
saccades - brings area of interest into the fovea
describe slow eye movement (3)
vestibulo-ocular reflex (VOR) - moves head at the same time
optokinetic reflex (OKR) - requires visual feedback
both maintain a stable image on the retina
what is meant by smooth pursuit ?
tracks moving objects
what meant by vergence ?
point eyes in the same direction
describe saccades (3)
ballistic - 40-200ms - too fast for sensory feedback
3 saccades a second
vision is actively suppressed during saccade
what are the 2 types of saccades ?
reflex - stimulus driven
voluntary - not stimulus necessary - looking anywhere
normal saccadic eye movements are characterised by what ?
slight undershoot
then followed by a corrective saccade
describe dysmetric saccades - in relation to the cerebellum
cerebellum important to tune saccadic eye movements
dysmetric saccades cause visual problem in cerebellar patients
what are the 2 types of dysmetric saccades ?
hypermetric - overshoot
hypometric - lots of small saccades required to move eye
how does the vestibule-ocular reflex (VOR) effect eye movement ?
rotates the eyes to compensate for head movement - when head moves keeps eyes in direction of object
stabilises visual image
what did research into VOR function in the dark reveal ? (5)
rotation in darkness used to test VOR function
creates alternating pattern of fast + slow eye movements known as NYSTAGMUS
quick saccades rest eye position
if VOR works correctly- slow phase eye rotation and head rotation cancel each other out - gain of 1
if les than gain of 1 then vestibular is damaged
describe VOR adaptation
relationship between head and scene movement required diff VOR gain
in real life when we get stronger glasses we adapt our VOR
what 3 things happen when the VOR goes wrong ?
anything affecting vestibular function compromises VOR
vestibular loss :head injury, viral infection , etc
loss of balance, disorientation, blurred vision
axing : vestibular hair cells lost with age
alcohol: changes in gravity of fluid in the canals - spinning sensation
what is the velocity storage system
continuous rotation causes vestibular decay quicker then eye movement
brain stem has velocity storage mechanism to prolong gaze stabilisation
but prolonged rotation causes the signal to fail - optokinetic reflex takes over
