H&N18 - Extraocular Eye Muscles

Question 1

Muscles of the eye and their innervation

Intrinsic x2
Extrinsic x2

Answer 1

1. ) Intrinsic Muscles - autonomic innervation
   - iris muscles (sphincter/dilator pupillae)
   - ciliary muscle controlling lens thickeness
2. ) Extrinsic Muscles - somatic innervation
   - extraocular muscles moving the eyeball
   - muscles of the eyelid (has some sympa innervation)

Question 2

5 features of the extraocular muscles and gaze

Primary Resting Gaze
Diplopia
Conjugate Gaze
Common Tendinous Ring
Axis of Orbit

Answer 2

1. ) Primary Resting Gaze - actions of muscles are balanced allowing for forward gaze
   - 2 eyes allows for depth perception enabling 3D vision
   - weakened muscle means other muscles actions are no longer antagonised so actions are not balanced
2. ) Diplopia - douple vision
   - occurs when visual axis of both eyes are not aligned
   - the further apart the visual axis, the worse the diplopia
3. ) Conjugate Gaze - ability of the eyes to work together
   - muscles must be highly coordinated and move simultaneously to ensure the visual axes remain aligned
4. ) Common Tendinous Ring - apex of the orbit
   - origin of all 4 rectus muscles and the 2 obliques
   - however, the obliques travels through the trochlea to insert into the posterior aspect of the globe
5. ) Axis of Orbit - extraocular muscles run in line with axis of orbit which is oblique to the visual axis
   - muscles attaching to superior and inferior surfaces attach at an oblique angle (SR, SO, IR, IO)
   - this means they have multiple actions on the globe

Question 3

Actions of the 6 extraocular muscles starting from primary resting gaze (and their insertion on the globe)

Innervation: LR6 SO4, the rest are 3

Lateral Rectus
Medial Rectus
Superior Rectus
Inferior Rectus
Superior Oblique
Inferior Oblique

Answer 3

1. ) Lateral Rectus - inserts onto lateral surface of the eye
   - abduction of the eye
2. ) Medial Rectus - inserts onto medial surface of the eye
   - adduction of the eye
3. ) Superior Rectus - superior anterolateral surface
   - elevates the eye and internally rotates
   - slightly adducts
4. ) Inferior Rectus - anteroinferior surface
   - depresses the eye and externally rotates
   - slightly adducts
5. ) Superior Oblique - superoposterior surface
   - depression and internal rotation of the eye
   - slightly abducts the eye
6. ) Inferior Oblique - inferoposterior surface
   - elevation and external rotation of the eye
   - slightly abducts the eye

• Rectuses slightly adduct, obliques slightly abduct
• superiors internally rotate, inferiors externally rotate

Question 4

clinical examination of the superior and inferior muscles

Midline Elevation and Depression
Testing Rectuses
Testing Obliques

Answer 4

1.) Need to isolate an action of each muscle to test them

2. ) Midline Elevation and Depression - combines actions of two muscles
   - SR and IO elevates the eye
   - IR and SO depresses the eye
3. ) Testing Rectuses - abduct the eye first to isolate the elevation and depression actions of SO and IO
   - then test elevation and depression
   - lateral position = testing SR and IR
4. ) Testing Obliques - adduct the eye first to isolate the elevation and depression actions of SR and IR
   - then test elevation and depression
   - medial position = testing SO and IO

Question 5

Cranial nerve palsies

Oculomotor
Trochlear
Abducens

Answer 5

1. ) Oculomotor (III) - innervates most of the extraocular muscle (apart from LR6 SO4)
   - also innervates majority of LPS and sphincter pupillae
   - in microvascular lesions, pupils are spared
   - in compressive lesions, pupils are involved
2. ) Trochlear (IV) - innervates superior oblique only
   - eyeball is extorted, elevated, adducted (up and in)
   - opposite of actions of superior oblique
   - patients can compensate for extortion by head tilting
   - worsening diplopia looking down and medially
3. ) Abducens (VI) - innervates lateral rectus
   - unable to abduct the affected eye
   - diplopia worse on adduction of unaffected eye

Question 6

steps in clinical examination of the eye (IVA FROM)

Inspect
Visual Acuity

Fields (visual)
Reflexes
Ophthalmoscopy
Movement of the Eye

Answer 6

1.) Inspect - general inspection, eye lids, conjunctiva, sclera

2. ) Visual Acuity - assessing one eye at the time
   - test near vision (30cm) record smallest print
   - test distance vision (6m) using snellen chart (score is distance of test/row number patient can read)
3. ) Visual Fields - test one eye at a time
   - compare directly with own eye
   - defects help localise pathology within visual pathway
   - lesion of optic nerve causes monocular blindness
4. ) Pupillary Reflexes
   - test accommodation reflex (pupil constriction)
   - test direct and consensual light reflex (pupil constricts to light stimulus)
5. ) Fundoscopy - looking at the optic disc for any sign e.g. papilloedema
6. ) Eye Movements - CN III, IV, VI tested simultaneously