The College of Optometrists

I've been doing some hospital experience for a while now, and I have just started attending the orthoptic clinic. While there, I thought I would ask the orthoptist something that has been bugging me for a while about AV patterns, and she could not come up with an answer. Whether this is because I am creating a problem from nothing remains to be seen:

Ok, take a V exo pattern. This arises from impaired adduction in up-gaze, and as such can arise from a number of things including superior rectus underaction. Now, this is the part that confuses me. The primary action of the superior rectus is isolated by asking a patient to look OUT (i.e. aBduction) and UP, or to aBduct the eye in upgaze. But when there is a deficiency in aDduction in upgaze, it is the superior rectus that is underacting. Where does this discrepancy arise? Similarly a V eso. Here it is a deficiency in abduction in downgaze, meaning the superior oblique may be faulty. But, to isolate the vertical componenent of the superior oblique during motility, you ask the patient to look down and in.

So am I creating a problem out of nothing here? Answers on a post card. Or just post in this forum.

When you are testing each muscle in isolation, you need to move the muscle into its field of action. By aBducting the eye, this makes the Superior Rectus a pure elevator, allowing you to test only superior rectus function, without any other muscle having an effect. This does NOT mean that the SR is an aBductor in elevation, it means that it is an elevator in aBduction.

In addition to elevation, the SR has two other actions, Intorsion, which we're not worried about at the moment, and aDduction. When the patient looks straight up (as when testing for V pattern) the SR is underacting, so there is decrased aDduction, and the IO overacts (because of weak SR) causing increased aBduction, combining to move the eyes outwards giving a V pattern.

The same logic can be applied to your V eso pattern.

Hope this makes some sense, but if not, let me know, since I know a friendly orthoptist who could probably explain it better.

aha...that does make sense. It's the difference between being, using the example of the superior rectus, an elevator in abduction, and an abductor in elevation. Similarly, I suppose, the superior oblique is a depressor in adduction, but not an adductor in depression.

Much obliged.

It's about remembering that there are different primary, secondary and tertiary actions of the EOMs, but where they are viewed may be different. E.g. the primary action of the SR is elevation, and this is maximum in ABduction. But it is not an abducting muscle.

Another good e.g. is the SO. This depresses, ABducts, and intorts. The intorsion is best seen in ADuction and depression, but if the patient has a 3rd nerve palsy they cannot depress or ADduct the eye. Therefore to check if the SO is intact, get the patient to look into ABduction and depression. As the SO works in that position, you will see some torsional movement if it is intact.