Pattern strabismus │A-V phenomena
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- Опубликовано: 13 май 2021
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And thank you so much, ma'am, for such a comprehensive video on pattern strabismus.
hi, may i know how differentiate exotropia with and without SO overaction? confuse with video at 3.27minute.
Depression is secondary action, & abduction is a tertiary action of the SO. So when SO is overacting, in down gaze - abduction action also overacts, resulting in divergence and therefore A pattern. At 3:27, in levodepression, there is no abduction, so the overaction manifests as overdepression
This is probably a terrible question to ask.
But I've never really understood why we say the action of superior oblique is intorsion, depression and abduction...and then we check the action of the muscle by asking the patient to adduct and depress the eye, same with diplopia charting.
I'm not even sure my question makes sense, I'm just really confused.
Please help me understand, ma'am.
That is a very good question. The two depressors of the eye are the superior oblique and the inferior rectus. If you remember, the obliques produce the majority of vertical actions in adduction, and the recti produce most of the vertical movements in abduction . So depression in adduction is mostly produced by the superior oblique. Hence if the superior oblique is weak, it stands to reason that we would like to check depression in adduction. So if you see evidence of less depression in adduction compared to in abduction, we conclude the superior oblique is weak. Let me know if that clears your doubt. If not, let me know what you need clarification on
@@ophthalmologypearls
Ma'am, so when we talk about extra ocular movements, it's different...and when we talk about diplopia charting/ Hess charting / checking for weakness it is about which muscle has maximum action in that particular position (adduction / abduction)?
@@XxxxxsilvermistxxxxX
Please open this link for access to a picture - read the rest of the explanation while looking at the picture.
drive.google.com/file/d/1pnXXmmvTGEwqP0hMx34QBKw5t59alD2s/view?usp=sharing
It is not different for extraocular movements. It is helpful to remember that the primary , secondary and tertiary actions are for the primary position mainly. The actions in other positions vary. For eg. in 39° abduction, the axis of the superior oblique tendon is perpendicular to the visual axis, and so cannot exert any vertical action. So it is a pure intorter in this position. In 51° adduction, the tendon axis and the visual axis are parallel. Here intorsion and abduction are not possible - only depression. That is why we check for this depressive action in adduction.
Is it clearer now?
@@ophthalmologypearls The inference from the diagram is that the superior (or inferior) oblique is a hundred percent effective in depression (or elevation) when the eye is adducted 51 degrees. And this action (depression or elevation) is ineffective when the eye is abducted 39 degrees.
This is because of the direction of insertion of the muscle.
So even though the SO os responsible for the abduction of the eye up to 39 degrees, we can't test vertical movements in this position.
Is this correct, ma'am?
@@XxxxxsilvermistxxxxX Yes that is right
Hi mam...could you please help me understand this?
We are checking superior oblique muscle overreaction with depression and abduction..but depression in abduction is brought about by inferior rectus na mam?
Could you please help me understand this 🥺
Hello @sripranavi6065,
You are right in saying that depression in abduction is brought about by inferior rectus. When checking for superior oblique action (underaction or normal), one should bring the eyeball into a position in which the only muscle that can cause intorsion is the superior oblique. In abduction, since the eyeball is perpendicular to the superior oblique tendon, the superior oblique cannot cause depression & in this position is a pure intorter. At the same time, both the vertical recti are now parallel to the eyeball, & therefore cannot perform intorsion/extortion. So absence of intorsion in abduction confirms superior oblique weakness