12. Eye movement

Question 1

What are the 2 gaze shifting classes?

Answer 1

Saccades and Vergence

Question 2

What is saccades?

Answer 2

Brings objects of interest onto the fovea

e.g looking between your two fingers very quickly

Question 3

What is vergence?

Answer 3

Disconjugate movement of eyes to allow BSV at different distances.

Question 4

What are the 4 classes for gaze holding?

Answer 4

1. Vestibular
2. Optokinetic
3. Smooth pursuit
4. Fixation

Vestibular and optokinetic work together

Question 5

What is vestibular class?

Answer 5

Holds retinal image steady during brief head rotation

Question 6

What is optokinetic class?

Answer 6

Holds retinal image steady during sustained head rotation

Question 7

What is smooth pursuit class?

Answer 7

Holds the image of a small moving target on the fovea.

e.g looking at a plane in the sky and tracking it.

Question 8

What is fixation class?

Answer 8

Holds eyes in primary position

Question 9

Explain neural control of eye movements

Answer 9

Frontal lobe, parietal lobe, occipital lobe (high cognitive areas) send info the the brain stem. To the pons where cranial nerves are.

Input from the high cognitive areas will arrive at excitatory burst neurons (horizontal and vertical). This then stimulates the III, IV and VI nerves to send signal to eye muscles.

If these were constantly firing our eyes would be jumping all over the place so are kept in check by omnipause neurons. The omnipause neurons turn off when Input from the high cognitive areas will arrive at excitatory burst neurons

Question 10

How are saccades generated?

Answer 10

Info processed in frontal eye field. This sends the info to:
1. The cerebellum which helps to compute the size and control the movement
2. The superior colliculus. This contains lots of cells to help dictate whereabouts in your visual field you will move your eyes to.
2a. The parietal cortex. Shifts out attention to a new area. and then sends to superior colliculus.

All of these signals then sent to brainstem nuclei.

Question 11

Disorders of Saccades

Answer 11

Velocity disorder = FEF /Parietal lesions. Extraocular muscle problem, brainstem abnormalities.

Initiation = delayed latency with FEF lesion

Amplitude (accuracy)= Dysmetria
Problem with cerebellar or brainstem
If hypermetria= problem with cerebellar

Question 12

Disorders of smooth pursuit

Answer 12

Slow jerky movement= Lesions in visual motion brain areas, FEF.

Question 13

Disorders with vergence

Answer 13

Convergence insufficiency
Brainstem lesions
High/Low AC/A ratios