Flashcards in Eye Movements 2 Deck (13)
A smooth pursuit eye movement is elicited by:
any large moving stimulus, and it is an attempt to foveate that stimulus for more extended visual examination.
Once the object is on/near the fovea, slower movements (pursuit) are used to track the moving object.
Smooth pursuit eye movements can only maintain foveation at a rate of ____. Why?
50 degrees per second or less.
Coordinating smooth pursuit requires a lot of analysis in the visual cortex.
You analyze the position, direction of movement and speed in the visual cortex, and this takes time.
At a speed greater than 50 degrees per second, the visual cortex cannot keep up, and so saccades are initiated at points during smooth pursuit to "catch up" with the object
At a speed greater than 50 degrees per second, the visual cortex cannot keep up, and so saccades are:
initiated at points during smooth pursuit to “catch up” with the object.
1. Fast and Accurate
2. Can occur in the dark w/o any visual stimulus
VOR is driven by
There are _____ for all directions of head rotation.
corresponding head-eye compensations
However many degrees your head moves in one direction, the eyes must move a corresponding amount in the opposite direction to maintain fixation on a certain point in space.
Rightward head rotation is signaled by the
1. if the head turns to the right, the eyes counter rotate left.
2. If the head continues to turn, the eyes rotate slowly left until the limit of eye rotation is reached, then snap quickly back to a new fixation point.
3. The sawtooth movement of the eyes – slow ramp opposite to head rotation, fast saccade to center of eye position
The direction of nystagmus is determined by
the direction of the rapid saccade “right-beating nystagmus”
Internuclear opthalmoplegia describes
the disconnection of the coordination of medial and lateral recti during horizontal gaze movements due to MLF damage.
early sign of MS
The MLF is
large, long, and myelinated. As such, it is vulnerable to demyelinating diseases, such as MS.
The medial rectus muscle and motor neurons may be normal even though
the muscle does not function properly during horizontal gaze. You can tease this out by doing a vergence test.