ORBIT & OCULAR ADNEXAE - Extraocular muscles Flashcards
What are the three intraocular muscles?
- ciliary muscle
- sphincter pupillae
- dilator pupillae
What are the three spaces in the orbit?
- extraconal space
- intraoconal space
- subperiosteal space
Where is the origin of the recti muscles?
Annulus of Zinn which encircles the optic foramen/canal and superior orbital fissure.
Which recti have adhesions with the dural sheath of the optic nerve?
What is the clinical inmportance of this?
superior rectus and medial rectus –> PAINFUL EYE MOVEMENTS IN OPTIC NEURITIS in upgaze and adduction
What is the tenons fascia?
Thin membrane which envelops the eyeball from optic nerve to corneal limbus
posteriorly - fused with optic nerve sheath
anteriorly - fuses with intermuscular septa 3mm posterior to limbus
What are the muscle pulleys around the extraocular muscles?
sleeves of connective tissue around rectus muscles as they penetrate tenon capsule - contain collagen, elastin and smooth muscle.
What is the function of the muscle pulleys around the extraocular muscles?
- Suspends muscle from adjacent orbital wall
- redirects muscle - acts as functional origin of muscle - only muscle fibres in front of muscle pulleys get displaced during movement.
- prevents displacement of muscle during movement
What is the angle between the orbital and optic axis?
22.5 degrees
How far apart are the medial walls from each other?
2.5cm
What is the angle betwen the two lateral walls?
What is the angle between the ipsilateral medial and lateral walls?
- 90 degrees
- 45 degrees
What is the angle of the superior and inferior recti muscles compared to the visual axis?
22.5 degrees (they follow the orbital axis)
What is the angle of the medial rectus compared to visual axis?
What is the angle of the lateral rectus compared to the visual axis?
- 0 degrees / parallel
- 45 degrees
What are the distance of insertion of recti from the limbus? What is this phenomenon called?
Spiral of Tillaux
SLIM RULE.
Superior rectus - 7.7mm
Lateral rectus - 6.9mm
Inferior rectus - 6.5mm
Medial rectus - 5.5mm
Where is the sclera the thinnest? How thin?
at insertion of the rectus (0.3mm) –> commonest site for perforation during severe blunt trauma to the globe
Which EOM has the shortest tendon length?
Inferior oblique.
Label the diagram.
What is the relation of LPS and SO compared to the SR?
Above SR - LPS
Below SR (insertion point only) - SO
Which muscles are supplied by the superior division of CNIII?
LPS and SR
Which muscles are supplied by the inferior division of CNIII?
MR, IR and IO.