IV CN Palsy Bilateral

[@bjurv]

How do we get eso in downgaze when the SO muscles are weak? To me surprising. What is the explanation?

[@TheGonagonagona]

Because on depression there is overaction of the inferior rectus which causes adduction.

[@hasnainpasha5343]

Since the tertiary function of SO (abduction) is also weakened so there is an eso shift.

[@madgirl809]

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[@hasnainpasha5343]

what about SR in bilateral SO palsy? are they overachieving or underachieving?

[@NeurologyAnalogy]

Hi, they are 'overachieving'. A nice thing to check on examination for is the chin down posture. This posture compensates for the unopposed eye elevators (SRs and IOs) as both superior obliques are affected. If it helps, I've created an animated video that explains this in detail.