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Ocular anatomy > Extraocular muscles > Flashcards

Extraocular muscles Flashcards

1
Q

What are the 6 Extraocular muscles in the eye

A

Superior recuts
Inferior recuts
Lateral recuts
Medial rectus

Superior oblique
Inferior oblique

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2
Q

What is three types of duction

A

Horizontal movement (along vertical axis)
- adduction, eye turns nasally
- abduction, eye turns temporally

Vertical movement (along transverse axis)
- elevation (supraduction)
- depression (infraduction)

tortinal movment (along sagittal axis)
- Intorsion (incycloduction), eyes rotate nasally
- Extorsion (excycloduction), eye rotates temporally

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3
Q

What is the primary posistion of gaze

A

Look straight, ahead position

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4
Q

What is the secondary posistion of gaze

A

Looking up, down, left or right

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5
Q

What is the tertiary posistion of gaze

A

Oblique position of gaze

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6
Q

what is the longest rectus muscle

A

SR, followed by MR, LR then IR

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7
Q

Where do the 4 recti start from

A

Annules of Zinn

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8
Q

Spiral of tillaux

A

MR attach closes to limbus, followed by IR, LR, SR (clockwise)

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9
Q

How is the superior rectus inserted into the sclera

A

passes laterally forward and pierces the sclera, 7.55mm posterior to limbus

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10
Q

What is the angle of visual axis for the Superior Rectus

A

Line of insertion is slightly curved and oblique, makes a angle of 23 degres with visual axis when eye in primary position

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11
Q

What is the primary action of superior rectus

A

Elevation
- at its maximum when eye is abducted 23 from primary position so that the visual line is parallel to the muslce pull

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12
Q

What is the seconday and tertiary action of superior rectus

A

Secondary action:
Intorsion

Teritary action:
Adduction
- 67 degrees from primary position so visual line is right angle to muslce pull

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13
Q

What is the nerve supply of superior rectus

A

Oculomotor (CN III) nerve

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14
Q

What is the blood supply of superior rectus

A

Muscular branch of opthalmic artery

Drained from superior opthalmic vein

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15
Q

How is the inferior rectus inserted into the sclera

A

passes laterally forward and pierces the sclera, 6.55mm posterior to limbus

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16
Q

What is the angleof visual axis for inferior rectus

A

23 degress with visual axis when eye in primary position

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17
Q

What is the primary action of the inferior rectus

A

Depression
- at its max. when eye abducted 23 degress from primary position so that visual line is parallel to muscle pull

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18
Q

What is the secondary and tetiary action of the inferior rectus

A

Secondary adction:
Extorsion

Tertiary action:
Adduction
- eye adducted 67 degress from primary position

How to rmb:
When ur Inferior= you depressed and extorsion, added tgt gives you 23 degress of depression

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19
Q

what is the nerve supply of inferior rectus

A

Oculomotr nerve

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20
Q

What is the blood supply of Inferior rectus

A

Ateries:
- Inferior muscular branch of opthalmic artery

  • Infra- orbital artery

Venous drainge:
- inferior opthalmic vein

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21
Q

How does the medial part peirce the scelra

A

Start from medial part of annulus, attached to dural sheath of optic nerve n medial wall of the orbit to form medial check ligment

Passes forward close to medial wall n pierces sclera area, inserts around 5.5mm from limbus

LARGEST EOM

22
Q

What is the action of the medial rectus

A

Adduction

23
Q

What is the nerve supply of the medial rectus

A

Occulomotor (CN III) nerve

24
Q

What is the blood supply of medial rectus

A

Supplied by inferior muscular branch of opthlamic artery

25
Q

How does the lateral rectus pierce the sclera

A

Spreads across the superior orbital fissure from the annulus, passes forward close to lateral wall of orbit, lie below lacrimal gland

Inserts about 7mm from limbus

26
Q

What is the action of the lateral rectus

A

Abduction

27
Q

Which nerve is the lateral rectus innervated by

A

Abducent Nerve (CN VI)

28
Q

What is the blood supply of the lateral rectus

A

Superior muscular branch and lacrimal branch of opthalmic artery

Drainage is inferior opthalmic vein

29
Q

How is the superior oblique inserted into the sclera

A

Inserted into periorbita at apex of orbit (medial n superior to annulus of zinn)

Runs nasally to trochlea fossa before tuning back to insert under the SR at upper lateral posterior quadrant of the globe

Longest and thinnest muscle

30
Q

What is the angle with the visual axis made by superior oblique muscle

A

Line of action of msucle make angle of 51 degres with sagital line when eye in primary position

31
Q

What is the primary action of the Superior Oblique muscle

A

Intorsion
- at its maximum when eye is abducted 39 degress from the primary position forming right angle to the musle pull

32
Q

What is the secondary and teritary action of the Superior Oblique

A

Secondary action:
Depression
- Max when eye is adducted by 51 degree from primary position so that visual line is parallell to muscle pull

Tertiary action:
Abduction
- at its max when eye is abucted by 39 degress from primary position forming right angle to muscle pull

33
Q

What is the nerve supply of the Superior Oblique

A

Trochlear nerve (CN IV)

34
Q

What is the blood suuply of the superior oblique

A

Muscular branch of the opthalmic artery

drainage from superior opthalmic vein

35
Q

How does the inferior oblique pierce the sclera

A

Only voluntary muscle within orbit that comes from front of orbit

Begins attachment at lateral edge of lacrimal fossa at anterior nasal margin of orbit and turns back between IR and the orbital floor to insert into sclera

SHORTEST EOM

36
Q

What is the angle with the visual axis made by inferior oblique muscle

A

Line of action of muscle makes an angle of 51 degress wth sagittal line when eyes in primary position

37
Q

What is the primary action of the inferior oblique muscle

A

Extorsion
- at its max when eye abducted 39 degress from primary position forming right angle to muscle pull

38
Q

What is the secondary and teritary action of inferior oblique muscle

A

Secondary action
Elevation
- at its max when eye is adduced by 51 degress from primary positon so that visual line is parallel to muscle pull

Tertiary action
Abduction
- at its maximum whn eye is abducted 39 degress from primary position forming right angle to muscle pull

39
Q

What is the nerve supply of the inferior oblique muscle

A

Inferior divions of oculmotor nerve( CN III)

40
Q

What is the blood supply of the inferior oblique muscle

A

Inferior muscular branch of opthalmic artery and branch of infra-orbital artery

Venous drainage from inferior ophthalmic vein

41
Q

what are the types of binocular eye movement

A

Version
vergence
saccades
smooth pursuits
Optokinetic nystagmus
Fixation eye movement

42
Q

What is version

A

Movement of two eyes in the same direction:

Dextroversion
- looking right

Laevoversion
- looking left

Supraversion
- looking up

Infraversion
- looking down

43
Q

What is Yoke muscle (contralateral synergists)

A

A pair of muscles one in each eye which contract stimultaneously during version movement

44
Q

what is hering’s law of equal innervation

A

Under this law, there is equal amount of innervation to the muscle in each eye that move the 2 eyes in the same direction (version)

45
Q

What is vergence

A

Movement of 2 eyes in the opp. direction to maitain single binocular vision

-convergence (nasally)
- divergence (temporally)

46
Q

What is saccades

A

Shift of gaze from one fixation point to another, usually voluntary intiated

Ends with slight reverse saccade (due to overshot of gaze), where lok boeyond the subject and come back to it

Fixation eye movement

47
Q

What is smooth pursuit movement

A

Voluntary eye movement to maintain foveal fixation on moving targets

Eyes move at same speed as target so taht image reminas stationary on retina

Target motion is needed to elicit smooth pursuit

48
Q

What is Optokinetic Nystagmus

A

A series of resolvable object move across the visual field, they will each be tracked for a short distance and then the fixation will be transferred to the next object

A type of induced nystagmus easily elicited in all person with a normal visual mechanism

49
Q

Give 2 scernations showing Optokinetic Nystagmus ( OKN)

A

When the body is in motion and the subject is gazing at the environment
- train nystagmus, when sitting in MRT and looking out the window

When the subject is still and the environment moves around them (rotating durm with stripes)

50
Q

How is OKN seen clinically

A

Use of rotating drum with striples on it
- starts iwht smooth pursuit folloowing a stripe until it passes out of visual field
- then a saccadic eye movment in the opposite direction trying to get a clear image on the fovea

This results in a jerk nystagmus

51
Q

What is fixation

A

Fixation mechanism works to maintain the object on the fovea

Small trembelling movements stil occur even when eye is in the steadiest position
- vibration from EOM

52
Q

What are the three types of fixational eye movement

A

Drift

Microsaccades

Tremors

Ocular anatomy (15 decks)

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