Session 9 Flashcards

Question

How do we change our position of gaze?

Answer 1

• Muscles moving both eyes must be highly co-ordinated and move simultaneously • Visual axes must remain aligned (conjugate gaze) • If visual axes maligned – Diplopia (“double vision”) • Some extraocular muscles have a single action on the eye • Some muscles exert several actions on the eye (depending on starting position of eyeball) • Extraocular muscles run in line with axis of orbit • Therefore some muscles attach to globe at an oblique angle – Those attaching to superior and inferior surfaces • Confers some muscles several ‘actions’ of movement on globe (not just simply ‘up’ and ‘down’) Images from sled 7 and 8 lec 2

Answer 2

Action each individual muscle exerts on the eyeball (at resting gaze…and when moving from primary resting gaze) Superior Rectus Muscle Elevates Eyeball but has some additional actions • SR (and IR) arise from apex of the orbit SR IR • SR inserts into superior anterolateral surface of globe • Action (if starting from primary resting gaze) – Elevate – Slightly adducts (pull eye medially) – Slightly intorts (internally rotates) Inferior Rectus Muscle Depresses Eyeball but has additional actions • IR inserts into anteroinferior surface of globe • Action (if starting from primary resting gaze) – Depress IR – Slightly adducts (pull eye medially) – Slightly extorts (externally rotates) Superior Oblique Muscle Intorts the Eyeball but also has depression action Trochlea* SO • Arises from apex of orbit, passes through trochlea, inserts into superoposterior aspect of globe IO – *consider the functional pull of SO being from the area of its trochlea • SO action (if starting from primary resting gaze) – Intort (internally rotate) – Depress – Slightly abducts (pull eye laterally) Inferior Oblique Muscle Extort the Eyeball but also has elevation action Trochlea SO IO • IO arises from anteromedial surface of floor of orbit; inserts into inferoposterior aspect of globe • Action of IO (if starting from primary resting gaze) – Extort (externally rotate) – Elevate – Slightly abduct (pulls eye laterally)

Answer 3

• Constancy of activity in all extra ocular muscles on the eyeball – At resting gaze, equal and opposite pull • If a muscle(s) weakened, its ‘influence’ (i.e. exerted by its anatomical action on the eyeball) is lost (or reduced) • Other muscle actions no longer antagonised (“balanced” out) – Resting position of eyeball may deviate = strabismus (squint) due to actions of remaining working muscles • Difficulties with moving eye in certain directions of gaze • Can be congenital or acquired e.g. cranial nerve lesions

Answer 4

Need to Isolate an Action of Each Muscle to Test Them .. H • Some muscles >1 action; some ‘share’ similar movements • Lateral and medial rectus – Straight forward as each only performs one action on the eye – Abduction (LR) and adduction (MR) of the eye Why the ‘H’? Why not… • But, elevation and depression (in midline) involves two muscles each + Starting From Resting Gaze (Midline) Elevation and Depression of the Eye Combine Actions of Two Muscles

Answer 5

Dominant Actions of SR/IR and Oblique Muscles Change if Starting Position of Eye is Changed • Move starting position of eye – Medially (adducting) first – or laterally (abducting) first • Then test elevation and depression • This isolates the elevation and depression actions of SR/IO and IR/SO which cannot be ‘isolated’ when testing from the midline Recti muscles are main elevator (SR) and depressor (IR) of the eye when the eyeball is starting from the lateral position Oblique muscles are main elevator (IO) and depressor (SO) of the eye when the eyeball is starting from the medial position

Answer 6

• Abnormalities of eye movements and diplopia • May be obvious from initial inspection of the eye – And/or become more apparent on testing eye movements • Cranial nerves III, IV, VI innervate muscles that move the eyeball • Can be affected by raised intracranial pressure (e.g. intracranial haemorrhage or tumour) • But all can also be affected by vascular disease (microvascular complications) from diabetes and hypertension • But all can also be affected by vascular disease (microvascular complications) from diabetes and hypertension

Answer 7

Cranial Nerve Palsies CN III Oculomotor • Most extra-ocular eye muscles innervated by CN III (except LR and SO) • Innervates majority of muscle of eyelid (LPS) and sphincter pupillae muscle • Vasculopathic (microvascular) lesions (e.g. diabetes/hypertension) – Pupil spared • Compressive lesions (raised ICP, tumour, posterior communicating artery aneurysm) – Parasympathetics run on periphery of CN III – Pupil involved

Answer 8

Cranial Nerve Palsies CN IV Trochlear • Innervates superior oblique muscle only • Superior oblique muscle acts to INTORT, and depress and abduct eye • Lose these actions so eyeball is held EXTORTED, slightly elevated and adducted • Compensate for the slight extortion of eyeball by tilting the head slightly (not seen in image) • Abnormality in gaze can be very subtle and often missed • Worsening diplopia (on downward vertical gaze) especially looking down and medially e.g. walking down stairs, reading – Remember SO is main depressor of the eyeball when in adduction

Answer 9

``` Cranial Nerve Palsies CN VI Abducens • Innervates lateral rectus • Unopposed pull of medial rectus muscle • Unable to abduct the eye on affected side • Report diplopia, made worse on horizontal gaze ```

Answer 10

• Most likely cause for CN III, ,IV and VI lesions is vasculopathic – Patients will be otherwise asymptomatic (apart from signs/symptoms directly relating to CN lesion) – Lesions usually self-resolve within few months • History will help give a clearer indication for more concerning underlying cause… – Headache (+/-) vomiting could suggest raised ICP (secondary to tumour or haemorrhage) – Recent head injury – Presence of pupil involvement in CN III lesions

Answer 11

Final slide of lec 2

Session 9 Flashcards

(35 cards)