Eye Movements 2

Question 1

A smooth pursuit eye movement is elicited by:

Answer 1

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.

Question 2

Smooth pursuit eye movements can only maintain foveation at a rate of ____. Why?

Answer 2

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

Question 3

At a speed greater than 50 degrees per second, the visual cortex cannot keep up, and so saccades are:

Answer 3

initiated at points during smooth pursuit to “catch up” with the object.

Question 4

VOR =

Answer 4

1. Fast and Accurate

2. Can occur in the dark w/o any visual stimulus

Question 5

VOR is driven by

Answer 5

vestibular input

Question 6

There are _____ for all directions of head rotation.

Answer 6

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.

Question 7

Rightward head rotation is signaled by the

Answer 7

horizontal canals.

Question 8

nystagmus

Answer 8

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

Question 9

The direction of nystagmus is determined by

Answer 9

the direction of the rapid saccade “right-beating nystagmus”

Question 10

Internuclear opthalmoplegia describes

Answer 10

the disconnection of the coordination of medial and lateral recti during horizontal gaze movements due to MLF damage.

early sign of MS

Question 11

The MLF is

Answer 11

large, long, and myelinated. As such, it is vulnerable to demyelinating diseases, such as MS.

Question 12

Internuclear opthalmoplegia:

The medial rectus muscle and motor neurons may be normal even though

Answer 12

the muscle does not function properly during horizontal gaze. You can tease this out by doing a vergence test.

Question 13

If a patient is unable to participate in horizontal gaze saccades or pursuit, yet can perform convergence eye movements:

Answer 13

then the patient likely has internuclear opthalmoplegia

(as opposed to, for example, CN III palsy).