Eye movement Flashcards
What are the different types of eye movements?
Fast –> Saccades
Slow –> VOR, OKR smooth pursuit and vergence
What are the properties of saccades?
Ballistic
Roughly 3 saccades per second
2 types: reflex and voluntary
Vision is actively suppressed during saccade
What is a corrective saccade?
Normal saccadic eye movement but with a slight undershoot followed by a corrective saccade
What do dysmetric saccades cause in cerebellar patients? and what are the 2 types?
cause visual problems
hypermetric and hypometirc
What is the VOR - vestibular-ocular reflex
rotates eyes to compensate for head movement, helps stabilise the visual image.
very fast - it is a basic brainstem circuit with only 3 neurons
How can you test VOR function?
- rotation in darkness produces alternating slow and fast movements. If Vor works perfectly then slow-phase eye movemnts should be cancelled out by head rotation
Anything that affects the vestibular system affects your VOR. What are the 3 main things?
Vestibular loss
ageing
alcohol
what is the velocity storage mechanism?
when spinning, the vestibular signal decays but your brain will still think you are because of gaze stabilization.
what takes over when the velocity storage mechanism fails?
optokinetic reflex
What is the optokinetic relfex?
Pretty much the same as VOR - rotates eyes to compensate for head movement but relies more of vision than the vestibular system
what is smooth pursuit?
ability to track a moving object. it involves some prediction as eyes will continue to move after the object disappears
What is vergence?
basically going cross eyed. (ability to direct eyes to same point)
what are the 4 methods of eye tracking?
scleral coil - contact lens with wire coils in. Measures yaw, pitch and roll
infrared reflectance - into the cornea
electro-oculography - retina gives electric charge
video-oculography - use software to track pupil
