Extraocular muscles Flashcards
What are the 6 Extraocular muscles in the eye
Superior recuts
Inferior recuts
Lateral recuts
Medial rectus
Superior oblique
Inferior oblique
What is three types of duction
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
What is the primary posistion of gaze
Look straight, ahead position
What is the secondary posistion of gaze
Looking up, down, left or right
What is the tertiary posistion of gaze
Oblique position of gaze
what is the longest rectus muscle
SR, followed by MR, LR then IR
Where do the 4 recti start from
Annules of Zinn
Spiral of tillaux
MR attach closes to limbus, followed by IR, LR, SR (clockwise)
How is the superior rectus inserted into the sclera
passes laterally forward and pierces the sclera, 7.55mm posterior to limbus
What is the angle of visual axis for the Superior Rectus
Line of insertion is slightly curved and oblique, makes a angle of 23 degres with visual axis when eye in primary position
What is the primary action of superior rectus
Elevation
- at its maximum when eye is abducted 23 from primary position so that the visual line is parallel to the muslce pull
What is the seconday and tertiary action of superior rectus
Secondary action:
Intorsion
Teritary action:
Adduction
- 67 degrees from primary position so visual line is right angle to muslce pull
What is the nerve supply of superior rectus
Oculomotor (CN III) nerve
What is the blood supply of superior rectus
Muscular branch of opthalmic artery
Drained from superior opthalmic vein
How is the inferior rectus inserted into the sclera
passes laterally forward and pierces the sclera, 6.55mm posterior to limbus
What is the angleof visual axis for inferior rectus
23 degress with visual axis when eye in primary position
What is the primary action of the inferior rectus
Depression
- at its max. when eye abducted 23 degress from primary position so that visual line is parallel to muscle pull
What is the secondary and tetiary action of the inferior rectus
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
what is the nerve supply of inferior rectus
Oculomotr nerve
What is the blood supply of Inferior rectus
Ateries:
- Inferior muscular branch of opthalmic artery
- Infra- orbital artery
Venous drainge:
- inferior opthalmic vein
How does the medial part peirce the scelra
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
What is the action of the medial rectus
Adduction
What is the nerve supply of the medial rectus
Occulomotor (CN III) nerve
What is the blood supply of medial rectus
Supplied by inferior muscular branch of opthlamic artery
How does the lateral rectus pierce the sclera
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
What is the action of the lateral rectus
Abduction
Which nerve is the lateral rectus innervated by
Abducent Nerve (CN VI)
What is the blood supply of the lateral rectus
Superior muscular branch and lacrimal branch of opthalmic artery
Drainage is inferior opthalmic vein
How is the superior oblique inserted into the sclera
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
What is the angle with the visual axis made by superior oblique muscle
Line of action of msucle make angle of 51 degres with sagital line when eye in primary position
What is the primary action of the Superior Oblique muscle
Intorsion
- at its maximum when eye is abducted 39 degress from the primary position forming right angle to the musle pull
What is the secondary and teritary action of the Superior Oblique
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
What is the nerve supply of the Superior Oblique
Trochlear nerve (CN IV)
What is the blood suuply of the superior oblique
Muscular branch of the opthalmic artery
drainage from superior opthalmic vein
How does the inferior oblique pierce the sclera
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
What is the angle with the visual axis made by inferior oblique muscle
Line of action of muscle makes an angle of 51 degress wth sagittal line when eyes in primary position
What is the primary action of the inferior oblique muscle
Extorsion
- at its max when eye abducted 39 degress from primary position forming right angle to muscle pull
What is the secondary and teritary action of inferior oblique muscle
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
What is the nerve supply of the inferior oblique muscle
Inferior divions of oculmotor nerve( CN III)
What is the blood supply of the inferior oblique muscle
Inferior muscular branch of opthalmic artery and branch of infra-orbital artery
Venous drainage from inferior ophthalmic vein
what are the types of binocular eye movement
Version
vergence
saccades
smooth pursuits
Optokinetic nystagmus
Fixation eye movement
What is version
Movement of two eyes in the same direction:
Dextroversion
- looking right
Laevoversion
- looking left
Supraversion
- looking up
Infraversion
- looking down
What is Yoke muscle (contralateral synergists)
A pair of muscles one in each eye which contract stimultaneously during version movement
what is hering’s law of equal innervation
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)
What is vergence
Movement of 2 eyes in the opp. direction to maitain single binocular vision
-convergence (nasally)
- divergence (temporally)
What is saccades
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
What is smooth pursuit movement
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
What is Optokinetic Nystagmus
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
Give 2 scernations showing Optokinetic Nystagmus ( OKN)
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)
How is OKN seen clinically
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
What is fixation
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
What are the three types of fixational eye movement
Drift
Microsaccades
Tremors
