extraocular muscles Flashcards
position of gaze
- Primary position of gaze (‘look straight’ ahead position)
- Secondary position of gaze (‘look up, down, left or right’)
- Tertiary position of gaze
> = Oblique position of gaze
the four rectus muscles
From among the recti, the MR is attached closest to the limbus, followed by IR, LR and SR forming a spiral of Tillaux
location of superior rectus
- It arises from the upper part of the Annulus of Zinn above the optic foramen
- The levator palpebrae superioris lies above the SR
superior rectus supply
nerve supplied by superior division of oculomotor nerve(CN III)
- Pierces SR and continue to supply the levator palpebrae superioris muscle
(raise the eyelids)
Blood supplied by:
- muscular branch of the ophthalmic artery
Venous drainage:
- superior ophthalmic vein
location of inferior rectus
the IR arises from the Annulus of Zinn, below the optic foramen
inferior rectus supply
Nerve
- Supplied by inferior division of the oculomotor (3rd) nerve
Blood supplied by
- Inferior muscular branch of the ophthalmic artery
- Infra-orbital artery
Venous drainage:
- Inferior ophthalmic vein
location of medial rectus
- it starts from the medial part of annulus
- attached to:
> dural sheath of the optic nerve
> medial wall of the orbit to form medial check ligament - Passes forward close to the medial wall of the orbit and pierces the sclera area
- largest EOM
medial rectus supply
nerve
- supplied by inferior division of oculomotor nerve (CN II)
blood
- supplied by inferior muscular branch of ophthalmic artery
venous drainage
- inferior ophthalmic vein
location of lateral rectus
Spreads across the superior orbital fissure from the annulus
lateral rectus supply
Nerve supplied by:
- abducent nerve(CN VI)
Blood supplied by:
- superior muscular branch
- Lacrimal artery from the ophthalmic artery
Venous drainage:
- Inferior ophthalmic vein
location of superior oblique
- Inserted into the periorbita at the apex of the orbit
(medial and superior to annulus of zinn) - Runs nasally to the trochlea fossa before turning back to insert under the SR at the upper lateral posterior quadrant of the globe
- longest and thinnest muscle
superior oblique supply
Nerve supplied by:
- Trochlear Nerve (4th Cranial Nerve)
Blood supplied by:
- Superior muscular branch of the ophthalmic artery
Venous drainage:
- Superior ophthalmic vein
location of inferior oblique
- The only voluntary muscle within the orbit that comes from the front of the orbit
- Begins attachment at the lateral edge of the lacrimal fossa at the anterior nasal margin of the orbit
- turns back between the IR and the orbital floor to insert into sclera
- It is the shortest EOM
inferior oblique supply
Nerve supplied by:
- Inferior division of the oculomotor (3rd) cranial nerve
Blood supplied by:
- Inferior muscular branch of the ophthalmic artery
- Branch of infra-orbital artery
Venous drainage:
- Inferior ophthalmic vein
EOM innervation
LR6 SO4 R3
- Lateral Rectus : 6th Cranial Nerve
- Superior Oblique : 4th Cranial Nerve
- Rest of the Muscles: 3rd Cranial Nerve
different types of binocular eye movement
- Version
> movement of 2 yes in the same direction - Vergence
> movement of two yes in opposite directions to maintain single binocular vision - Saccades
> shift of gaze from one fixation point to another - Smooth pursuits
> eyes move at the same speed as the target so that the image remains stationary on the retina - Optokinetic nystagmus
- Fixation eye movement
> Fixation mechanism works to maintain the object on the fovea
EOM movement
medial rectus
- primary: adduction
lateral rectus
- primary: abduction
inferior rectus
- primary: depression
- secondary: extorsion
- tertiary: adduction
superior rectus
- primary: elevation
- secondary: intorsion
- tertiary: adduction
inferior oblique
- primary: extorsion
- secondary: elevation
- tertiary: abduction
superior oblique
- primary: intorsion
- secondary: depression
- tertiary: abduction
