Upload
scot-dawson
View
217
Download
3
Tags:
Embed Size (px)
Citation preview
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:
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:
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
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
Extrinsic eye muscles: Theory and testing
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
To help us understand this problem, we have:
1. A (very) quick quiz2. Some diagrams to label
i. Muscle attachments/forcesii. Actions of eye muscles ‘alone’iii. ‘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
Nose Nose Nose
LR MRSR
SO
IR
IO
Indicates action below eye
MRLR
IO
SO
SR
IR
SR
IR SO
IO
LR MR
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
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
What is the meaning of....
“LR6 Sulphate” ????
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
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
http://cim.ucdavis.edu/EyeRelease/Interface/TopFrame.htm
Including quiz…….
Extrinsic eye muscles: Theory and testing
• 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….
Extrinsic eye muscles: Theory and testing
• 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
IRNose
“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
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
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
• 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….
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.
1. Retina (usually pendular)2. Vestibular system (fast phase towards side of
lesion)3. Brain - cerebellum or brainstem (fast phase
towards side of lesion)