Eye movements Flashcards
What are the 4 types of eye movements?
smooth pursuit, saccades, vestibuloocular reflex and optokinetic nystagmus, vergence
What is the purpose of smooth pursuit?
tracking –> keep an object on the fovea
What is a saccade?
700 degree/sec ballistic movement used to rapidly foveate an interesting peripheral visual stimulus or restore the eye toward the center of the orbit
How is a saccade generated?
High frequency (1000 Hz) burst –> initial acceleration –> calculation of steady rate –> maintained new eye position
Describe conjugate eye movements
eyes move in the same direction. Initiated by visual and vestibular inputs
Describe vergence movements
eyes move in opposite directions. Eg: accomodation reflex –> focus on near object
What is the speed of smooth pursuit movements?
50 degrees/sec
How is foveation maintained for an object moving faster than 50 degrees/sec?
combination of saccade and smooth pursuit
Describe the control of the vestibuloocular reflex for a person sitting on a chair that is rotated to the right
Rightward head rotation sensed by semicircular canals –> fluid rotates left –> deflection of the cupula (right side = depolarization; left side = hyperpolarization) –> excitation transmitted to the right vestibular nuclei –> MLF –> left lateral rectus neurons in abducens nucleus; right medial rectus contraction due to coactivation of abducens and internuclear interneurons –> maintained center of gaze
What is interocular ophthalmoplegia?
MLF damage –> uncoordinated medial and lateral recti during horizontal gaze movements
How do you determine the medial rectus motor neuron function
test vergence movements –> both medial recti contract
What is optokinetic nystagmus
Rhythmic pattern of saccades and tracking movements. Experienced by watching a passing scene, such as telephone poles from a moving vehicle
What is vestibular nystagmus?
Continuous head rotation (spinning in circles) –> eyes go to limit of eye rotation –> eyes snap to new fixation point. “Sawtooth” movement of eyes
