Visual system- eye movements

Question 1

what is duction?

Answer 1

eye movement in one eye

Question 2

what is version?

Answer 2

simultaneous movement of both eyes in same direction

right= dextroversion

left= levoversion

Question 3

what is vergence?

Answer 3

1. simultaneous movement of both eyes in opposite direction

Question 4

what is convergence?

Answer 4

1. simultaneous adduction (inward) movement in both eyes when viewing a near target

Question 5

what is a saccade?

Answer 5

short fast burst of eye movement

can be voluntary or involuntary

Question 6

what are the types of saccade?

Answer 6

1. reflexive saccade to external stimuli (acquiring new external target)
2. scanning saccade (reading book)
3. predictive saccade to track objects
4. memory-guided saccade (in absence of external stimuli)

Question 7

what is a slow pursuit?

Answer 7

sustained slow eye movement - up to 60deg/sec

driven by motion of moving target across the retina

Question 8

what are the extraocular muscles?

Answer 8

Question 9

Where do the extraocular muscles originate?

Answer 9

5/6 from back of orbit

inferior oblique comes nasally

Question 10

where does the superior rectus attach and what do they do?

Answer 10

attached to eye at 12 o clock

elevates the eye maximally, moves eye up

Question 11

where does the inferior rectus attach and what does it do?

Answer 11

attached to eye at 6 o clock

depressses eye maximally (moves eye down)

Question 12

what does the lateral rectus do and where does it attach?

Answer 12

also called external rectus, attaches on temporal side of eye, moves eye towards outside of head (towards temple)

Question 13

what does the medial rectus do and where does it attach?

Answer 13

also called internal rectus, attaches on nasal side of eye, moves the eye towards the middle of the head (towards the nose)

Question 14

where is the superior oblique attach and what does it do?

Answer 14

attached high on temporal side of eye

passes under superior rectus

moves eye in a diagonal pattern down and out

travels through trochlea

Question 15

what does the inferior oblique do and where is it attached?

Answer 15

(faded muscle)- attached low on nasal side of eye and passes over inferior rectus. Moves eye in diagonal pattern (up and out)

Question 16

what is the innervation of extraocular muscles?

Answer 16

Question 17

which muscle in involved in looking in each direction?

Answer 17

Question 18

how is extraocular muscle testing done?

Answer 18

– Isolate muscle to be tested by maximizing its action and minimizing the action of other muscles

Question 19

what muscle is used for each movement of eye?

Answer 19

• Abduction – Lateral Rectus
• Adduction – Medial Rectus
• Elevated and Abducted – Superior Rectus
• Depressed and Abducted – Inferior Rectus
• Elevated and Adducted – Inferior Oblique
• Depressed and Adducted – Superior Oblique

Question 20

what is a 3rd nerve palsy?

Answer 20

• Only muscles not innervated by 3^rd cranial nerve are working

Question 21

what are the signs of a 3rd nerve palsy?

Answer 21

• Affected eye down and out
• Droopy eyelid (ptosis) (loss elevator palprebrae superioris- upper lid lavatory muscle innervated by superior branch of oculomotor nerve (3^rd))
• Unopposed superior oblique innervated by 4^th nerve (down)
• Unopposed lateral rectus action innervated by 6^th nerve (out)

Question 22

what happens in a 6th nerve palsy?

Answer 22

• Affected eye unable to abduct and deviates inwards
• Double vision worsen on gazing to the side of affected eye

Question 23

what are the causes of 3rd, 4th and 6th nerve palsy?

Answer 23

Question 24

what is nystagmus?

Answer 24

oscillatory eye movement

Question 25

what is optokinestic nystagmus?

Answer 25

smooth pursuit + fast phase reset saccade

• Eyes track along grating motion, with smooth pursuit up to a limit and resets eye position to centre with a burst of fast saccade motion
• Results in cycles of slow phase smooth pursuit, alternating with fast phase reset saccade in opposite direction

Question 26

what is an optokinetic nystagmus reflex useful for?

Answer 26

testing visual acuity in pre-verbal children

by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies

signifies subject has sufficient visual acuity to perceive the grating pattern