Topic 11: Extra Ocular Muscles Flashcards
describe extra ocular muscles
originate from annulus of zinn
the four recti muscles are seen anteriorly - arrangement: spiral of tillaux
the two oblique muscles are seen posteriorly
state the 9 directions of gaze
1 primary position: looking straight ahead focused at infinity
4 secondary positions: rotations around either vertical or horizontal axis (left, right, up, down)
4 tertiary positions: around both vertical and horizontal axes (up-left, up-right, down-left, down-right)
NOTE: up=supraversion, down=infraversion, right=dextro, left=levo
explain monocular eye movements
aka DUCTIONS: movement of one eye
NOTE: move.. up=supraduction/elevation, down=infraduction/depression, in/nasally=adduction, out/temporally=abduction
rotations of upward cornea NOTE: rotate.. in/nasally=InCycloduction, out/temporally=ExCycloduction
^ intorsion / extorsion
state & describe the two types of binocular eye movements
versions: both eyes move together towards same direction. AKA conjugate eye/tracking eye movements
vergence: both eyes move in opposite directions. AKA dis-conjugate eye movements
explain versions
4 secondary gaze positions + 2 rotation versions (InCycloversion & Excycloversion)
explain vergence
horizontal plane rotations: convergence (towards midline) & divergence (laterally)
anterior-posterior axes: incyclovergence & excyclovergence
explain herring’s law
herrings law of equal innervation to yoke muscles
-YM: one muscle from each eye that work together in the same direction (eg, RLR & LMR)
eg. dextroversion: for both eyes to move to the right, RLR & LMR have to contract equally
explain sherrington’s law
sherrington’s law of reciprocal innervation to antagonistic muscles
-AM: 2 muscles of the same eye that work in opposite directions. when one muscle is stimulated, its antagonist is inhibited. (eg. RLR & RMR)
eg. dextroversion: for RE to move right, RLR contracts & RMR relaxes
summarise the monocular actions of EOM (primary & secondary)
OLAB2nd SIE RADEL
OLAB2nd - ‘all obliques are abductors secondary’
SIE - ‘superiors are intorsioners’ & ‘inferiors are extorsioners’
RADEL - ‘recti are adductors except lateral (abuctor)’
state nerve supply
(LR6 SO4)3
CN3=oculomotor, CN4=trochlear, CN6=abducens
state blood supply
muscular branches of ophthalmic artery
NOTE: inferior EOM (IO, IR) also supplied by infraorbital artery (ECA). superior EOM (SO, SR) also partly supplied by supraorbital artery (OA < ICA)