OM Nerve palsy characteristics Flashcards
What is Herring’s law?
Agonists on versions are innervated equally.
e.g. RMR and LLR
What is Sherrington’s law?
Antagonists on ductions have equal and opposite innervation.
e.g. RMR and RLR
What is muscle sequelae?
Limitation of movement in a direction of gaze affecting innervation of other EOMs in a sequential fashion.
What order does muscle sequelae occur in?
- Primary muscle underaction
- Overaction of contralateral synergist
- Overaction of ipsilateral antagonist
- Inhibition of contralateral antagonist
What does the extent of muscle sequelae depend on?
Duration of palsy (longer = further development)
Degree of limitation (bigger = larger sequelae)
Fixing eye (if fixing is palsied, less sequelae)
How can nerve palsies be controlled?
Fusion
AHPs
Which direction does someone with an AHP turn?
Towards position where deviation is the least - reduces double vision.
Opposite to deviation.
For a horizontal deviation, what type of AHP will occur?
Head turn
For a vertical deviation, what type of AHP will occur?
Head tilt towards lower eye
Why might an AHP be used when an AV pattern is present?
To put eyes in the position where the deviation is the least.
e.g. in eso V: chin down to put eyes in elevated position where there is no/less deviation
What are some other reasons someone may use an AHP?
Unilateral blindness - turn towards blind eye
Avoid pain/discomfort in a particular direction
Increase deviation (separate diplopic images)
Obtain foveal fixation with very restricted movement
Ptosis - elevate to achieve fixation or BSV
What is a V pattern?
Divergence on elevation
Convergence on depression
15D difference between angles
What is an A pattern?
Convergence on elevation
Divergence on depression
10D difference between angles
What is a Y pattern?
Divergence on elevation
What is an upside down Y pattern?
Divergence on depression
What is an X pattern?
Divergence on elevation and depression
What is a diamond pattern?
Convergence on elevation and depression
What are the treatment options for AV patterns?
Prism (only if symptomatic)
Surgery: if cosmetically poor, sxs or decompensation is prevented by large AHP.
What is the aim of surgery for AV patterns?
Reduce horizontal deviation in primary position, aiming for control, and restoring concomitance in elevation and depression.
