Extrinsic eye muscles: Theory and testing

Extrinsic eye muscles: Theory and testing Adam Pearce & Emily Matthews

You are on your first F1 rotation in Neurology. On your ward round, you notice a chap whose right eye is in the following, abnormal, resting position: Extrinsic eye muscles; Theory and testing

By the end of this session, you should be able to state which eye muscles are affected, and describe why they are having this effect: Extrinsic eye muscles; Theory and testing

To help us understand this problem, we have: • A (very) quick quiz • Some diagrams to label • A (not very) cryptic riddle • An online resource • A case Extrinsic eye muscles; Theory and testing

To help us understand this problem, we have: • A (very) quick quiz • Some diagrams to label • A (not very) cryptic riddle • An online resource • A case Extrinsic eye muscles: Theory and testing

Q: What are the names of the six extrinsic eye muscles? • Lateral rectus • Medial rectus • Superior rectus • Inferior rectus • Superior oblique • Inferior oblique Extrinsic eye muscles: Theory and testing

To help us understand this problem, we have: • A (very) quick quiz • Some diagrams to label • Muscle attachments/forces • Actions of eye muscles ‘alone’ • ‘The Big H’ – Testing Extrinsic eye muscles: Theory and testing

On the plan view of a right eye, below, show the point of attachment and action of force of each of the extrinsic eye muscles: On the frontal view of a right eye, below, label the appropriate direction that each muscle causes the eye to move, if acting alone On the frontal view of a right eye, below, label the appropriate direction that we use to test each eye muscle LR MR SR IR SR SR IO IO MR LR LR MR SO IO SO IR SO IR Nose Nose Nose Indicates action below eye Extrinsic eye muscles: Theory and testing

To conceptualise the action of the Right Superior Oblique, assume your left arm is the muscle and your head is the right eyeball…. Extrinsic eye muscles: Theory and testing

What is the meaning of.... “LR6 Sulphate” ???? Extrinsic eye muscles: Theory and testing

What is the meaning of.... “LR6Sulphate” ???? Lateral rectus = Cranial Nerve 6 (abducens) Extrinsic eye muscles: Theory and testing

What is the meaning of.... “LR6 Sulphate” ???? Sulphate = SO4 Superior Oblique = Cranial Nerve 4 (trochlear) Extrinsic eye muscles: Theory and testing

What is the meaning of.... “LR6 Sulphate” ???? The rest of the extrinsic muscles are innervated by cranial nerve 3 (oculomotor) Extrinsic eye muscles: Theory and testing

The innervation of the extrinsic eye muscles: = “LR6 SO4” Lateral Rectus = CN6 Superior Oblique = CN4 The rest = CN3 Extrinsic eye muscles: Theory and testing

http://cim.ucdavis.edu/EyeRelease/Interface/TopFrame.htm Including quiz……. Extrinsic eye muscles: Theory and testing

Patient is trying to follow green dot  Extrinsic eye muscles: Theory and testing

And turning that on its head…. • The simulator quiz shows us one way that we can look at these problems • See the symptom and diagnose the muscle or cranial nerve that must be damaged • Another way to look at these problems is: • Know which cranial nerve has been damaged and predict the symptoms due to extrinsic eye muscle damage. Extrinsic eye muscles: Theory and testing

So, going back to our diagrams…. • What would be the resting position of the right eye if we were to lose the right Cranial Nerve 3? SR IO MR LR SO IR Nose “Down and Out” Position Extrinsic eye muscles: Theory and testing

By the end of this session, you should be able to state which eye muscles are affected, and describe why they are having this effect: Affected muscles: - R. Medial rectus - R. Superior rectus - R. Inferior rectus - R. Inferior oblique Why? - R. Oculomotor nerve palsy. Extrinsic eye muscles; Theory and testing

An adult diabetic man presents with: • sudden right facial swelling • right proptosis • complete right ophthalmoplegia Extrinsic eye muscles: Theory and testing

Which cranial nerves must be damaged to cause complete opthalmoplegia? • Oculomotor (CN3) • Trochlear (CN4) • Abducens (CN6) Extrinsic eye muscles: Theory and testing

Where within the cranium can a single lesion affect each of these cranial nerves? Cavernous sinus Extrinsic eye muscles: Theory and testing

An adult diabetic man presents with: • sudden right facial swelling • right proptosis • complete right ophthalmoplegia Right cavernous sinus thrombosis: Extrinsic eye muscles: Theory and testing

And if we have time…. • What is the definition of Nystagmus? • “…..a repetitive, involuntary, to-and-fro oscillation of the eyes.” [http://www.patient.co.uk/doctor/nystagmus] Extrinsic eye muscles: Theory and testing

Extrinsic eye muscles: Theory and testing

What are the three main classifications of nystagmus (based on the type of movement)? • Pendular - movement that is equal in rate in both directions, like a clock's pendulum • Jerk - slow component and a fast component in opposite direction. Named according to direction of fast phase • Mixed Extrinsic eye muscles: Theory and testing

Give two situations in which we might see a physiological nystagmus. • End-point – fine jerk nystagmus at the extremes of gaze. The fast phase is in the direction of the gaze. • Optokinetic – eg. when following a moving object out of a train window. This is a jerk nystagmus – the slow phase follows the first object, and the fast phase locks onto the next object. Extrinsic eye muscles: Theory and testing

Give three structures that, when damaged, can give rise to a pathological nystagmus. • Retina (usually pendular) • Vestibular system (fast phase towards side of lesion) • Brain - cerebellum or brainstem (fast phase towards side of lesion) Extrinsic eye muscles: Theory and testing

That’s all, folks.... Adam Pearce & Emily Matthews

Extrinsic eye muscles: Theory and testing