Extrinsic eye muscles: Theory and testing

Extrinsic eye muscles:

Theory and testingAdam Pearce & Emily Matthews

Extrinsic eye muscles; Theory and testing

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:


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:


To help us understand this problem, we have:

1. A (very) quick quiz2. Some diagrams to label3. A (not very) cryptic riddle4. An online resource5. A case

Extrinsic eye muscles: Theory and testing




Q: What are the names of the six extrinsic eye muscles?

1. Lateral rectus2. Medial rectus3. Superior rectus4. Inferior rectus5. Superior oblique6. Inferior oblique






1. A (very) quick quiz2. Some diagrams to label

i. Muscle attachments/forcesii. Actions of eye muscles ‘alone’iii. ‘The Big H’ – 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

Nose Nose Nose

LR MRSR

SO

IR

IOIndicates action below eye

MRLR

IO

SO

SR

IR

SR

IR SO

IO

LR MR


To conceptualise the action of the Right Superior Oblique, assume your left arm is the muscle and your head is the right eyeball….





What is the meaning of....

“LR6 Sulphate” ????




Lateral rectus = Cranial Nerve 6 (abducens)




Sulphate = SO4

Superior Oblique = Cranial Nerve 4 (trochlear)




The rest of the extrinsic muscles are innervated by cranial nerve 3

(oculomotor)


The innervation of the extrinsic eye muscles:

= “LR6 SO4”

Lateral Rectus = CN6

Superior Oblique = CN4

The rest = CN3





http://cim.ucdavis.edu/EyeRelease/Interface/TopFrame.htm

Including quiz…….




Patient is trying to follow green dot


Patient is trying to follow green dot


• 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.

And turning that on its head….


• What would be the resting position of the right eye if we were to lose the right Cranial Nerve 3?

So, going back to our diagrams….

MRLR

IO

SO

SR

IR Nose

“Down and Out” Position


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.





An adult diabetic man presents with:

• sudden right facial swelling• right proptosis• complete right ophthalmoplegia


Which cranial nerves must be damaged to cause complete opthalmoplegia?

• Oculomotor (CN3)• Trochlear (CN4)• Abducens (CN6)


Where within the cranium can a single lesion affect each of these cranial nerves?

Cavernous sinus


An adult diabetic man presents with: • sudden right facial swelling• right proptosis• complete right ophthalmoplegia

Right cavernous sinus thrombosis:


• What is the definition of Nystagmus?

– “…..a repetitive, involuntary, to-and-fro oscillation of the eyes.”

[http://www.patient.co.uk/doctor/nystagmus]

And if we have time….

http://www.patient.co.uk/doctor/nystagmus



• 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


• 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.


• Give three structures that, when damaged, can give rise to a pathological nystagmus.

1. Retina (usually pendular)2. Vestibular system (fast phase towards side of

lesion)3. Brain - cerebellum or brainstem (fast phase

towards side of lesion)

That’s all, folks....

Adam Pearce & Emily Matthews

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Extrinsic eye muscles: Theory and testing