Eye Movement

Question 1

Why do we move our eyes

Answer 1

To bring points of interest over the fovea

To prevent blurring of the visual scene

Question 2

Describe the types of eye movement

Answer 2

Fast: saccades- brings the area of interest onto the fovea

Slow: vestibulo-ocular reflex maintains a stable image on the retina

Question 3

Describe saccades

Answer 3

1.ballistic: up to 900 degrees last up to 40-200ms (too fast for sensory feedback)

2.roughly 3 saccades per second: more frequent than heartbeats, 10% of waking hours spent making saccades

3.two types: reflex and voluntary

4. Vision actively suppressed during a saccade

Question 4

Corrective saccades

Answer 4

Normal saccadic eye movement often characterised by slight undershoot followed by a corrective saccade

Question 5

What do dysmetric saccades cause

Answer 5

Cause visual problems in cerebellar patients

Question 6

What does the vestibular system consist of

Answer 6

3 semicircular canals- detect head rotation

2 otolith organs- detect tilt and linear acceleration

Question 7

VOR Adaption

Answer 7

1. Different relationship between head and scene movement requires different VOR gain
2. Adaption can be demonstrated experimentally with rotating chair and curtain
3. Cerebellar disease impairs VOR adaption

Question 8

What can cause vestibular loss

Answer 8

Infection, head injury, surgical intervention. Symptoms include loss of balance, disorientation and oscillopsia

Question 9

What is the velocity storage mechanism

Answer 9

The brainstem has a velocity storage mechanism to prolong gaze stabilisation.

However during prolonged rotation this signal fails

Question 10

What is vergence

Answer 10

Ability to direct eyes toward the same point

Disordered vergence may underlie some types of dyslexia