Extraocular muscles

Question 1

What is the primary action of MR?

Answer 1

Adduction

Question 2

Primary action of SO

Answer 2

Incylcotorsion

In adduction, primary action is depression

Question 3

Primary action of IO

Answer 3

Excyclotorsion

Question 4

Priamry action of SR

Answer 4

Elevation

Question 5

Primary action of IR

Answer 5

Depression

Question 6

What is function of SO / IO in adduction

Answer 6

SO - depression in adduction
IO - elevation in adduction

Question 7

What are yoked muscles?

Answer 7

Contract to move both eyes in the same direction

Question 8

What are yoked muscles of looking right?

Answer 8

Right lateral rectus, left medial rectus

Question 9

What are yoked muscles of looking left?

Answer 9

Right medial rectus, left lateral rectus

Question 10

What are yoked muscles of looking right and up?

Answer 10

Right superior rectus
Left inferior oblique

Question 11

What are yoked muscles of looking right and down?

Answer 11

Right inferior rectus
Left superior oblique

Question 12

What are yoked muscles of looking left and up?

Answer 12

Left superior rectus
Right inferior oblique

Question 13

What are yoked muscles of looking left and down?

Answer 13

Left inferior rectus
Right superior oblique

Question 14

What is the fucntion of superior rectus?

Answer 14

Elevation (max when eye abducted 24)

Incyclotorsion (maximal on adduction or medial gaze)

Question 15

What is the fucntion of inferior rectus

Answer 15

Depression ( max when eye abducted 24

Excyclotorsion (maximal in adduction)

Question 16

What is the fucntion of the superior colliculus?

Answer 16

rostral midbrain
Coordinates gaze shifts involving eye and head movement

Question 17

What is the cerebellar vermis invovled in?

Answer 17

Initiation of eye movements

Question 18

What are the frontal eye fields involved in?

Answer 18

Mediate contralateral saccadic eye movements

Question 19

What is version vs vergence?

Answer 19

Version is movement of both eyes in the same direction

Vergence is movements in different direction

Question 20

What is smooth pursuit movement?

Answer 20

Designed to keep an object of interest on the fovea

Emanate from occipitoparietal region

Question 21

What is Cogan’s law?

Answer 21

Desctructive lesions in occipitoparietal region may disrupt smooth pursuit to the ipsilateral side

Asymmetrical optokinetic nystagmus results

Question 22

What are saccadic movmeents?

Answer 22

Designed to place an object of interest in the peripheral visual field on the fovea

Fastest eye movements

Controlled by frontal cortex

Question 23

What are fixation movements?

Answer 23

Move the retinal image by very small intervals and prevent the image from fading due to persistent bleaching of photoreceptor pigments

Question 24

What is TRoxler’s phenomenon

Answer 24

image fading due to persistent bleaching of photoreceptor pigments

Question 25

What is optokinetic nystagmus?

Answer 25

Biphasic movmeent that can be elicited by a striped drum revolving at 30 to 100 degrees per second Smooth pursuit is compensatory movement followed by quicker saccadic movement

Question 26

What is Floren's law

Answer 26

Stimulation of semicircular canal leads to nystagmus in the plane of that canal, the slow phase of which is always in a direction opposite to that causing the nystagmus

Question 27

Describe caloric testing

Answer 27

Warm water stimulates horizontal canal causing smooth eye movement to contralateral side and saccadic movement to ipsilateral side Cold water stimulates horizontal canal causing smooth eye movement to ipsilateral side and saccadic movement to contralateral side COWS Cold opposite, warm same (nystagmus)

Question 28

What type of muscle fibres are EOM composed of?

Answer 28

Twitch-tonic type fibres Twitch - fast acting with en plaque motor nerve terminals - speed of response for eye tracking and vestibuloocular reflex Tonic - slow but fatigue resistance with en grappe motor terminals for holding gaze

Question 29

What angle isolates primary action of obliques

Answer 29

39512367 39 degrees abduction OBLIQUES ARE ABS SO - extorts IO - intorts

Question 30

What angle isolates secondary action of obliques

Answer 30

51 degrees ADDUCTION ABD FIRST ADD 2 SO - depresses IO - elevates

Question 31

What angle isolates primary action of SR IR

Answer 31

23 degrees ABDUCTION SR elevates IR depresses

Question 32

What angle isolates secondary action of SR IR

Answer 32

67 degrees ADDuction ABD 1 ADD 2 SR intort IR extort

Question 33

What action to superior muscles have

Answer 33

INTORT

Question 34

What action to inferior muscles have

Answer 34

EXTORT

Question 35

What are tertiary action of obliques

Answer 35

ABDuction obliques are abs