Thursday, January 31, 2008

Extraocular Muscle Movements - Function Explained


Usually, anatomists and clinicians share the same base of knowledge regarding how the body functions. However, as I was doing Step I practice questions today, I came across a question that referred to the functions of the extra-ocular muscles. As I flipped through First Aid for the USMLE Step 1, I noticed that the section on extra-ocular muscles had been visited by me before:

Abduction:
Inferior oblique
Superior rectus
Inferior oblique

...

Apparently, I had reviewed this topic at various times and found varying results from different sources. I decided to end this once and for all with the med student's almost authoritative resource: Wikipedia. The page that came up was helpful, but Wikipedia posed more questions than it answered. Apparently, clinicians in the past believed that the obliques adducted, while anatomists begged to differ. Luckily, a reference to a British Medical Journal article resolved the issue: the anatomists won, the obliques abduct.

It is interesting to see how someone's mistake if inculcated enough can become dogma. Simply by looking at the muscles, as was pointed out to me, the actions are apparent. As the obliques attach on the temporal aspect of the orbit, when they contract, the orbit will rotate against the force around its axis. In other words, the eye will abduct. How clinicians missed this for apparently a long time is beyond me. However, the British have a theory:

Our final conclusions, and what is now our policy for instruction on this muscle, is as follows. The superior oblique, acting in isolation, turns the eye down and out. However, if it was tested clinically by the patient being asked to look down and out, its action could be mimicked by the combined action of inferior and lateral recti. This is particularly so as the inferior rectus acts most effectively when the eye is abducted (looking laterally). Thus if the patient is asked to look down and in, these muscles are excluded and the problem is solved. Essentially we are testing the ability of the superior oblique to look downwards.

The confusion, which I hope the above clarifies, is compounded by some ophthalmologists being so used to testing the muscle by asking the patient to look down and in that they have forgotten that the isolated action is down and out.
Ah ha! So it was the ophthalmologists' fault! Well, well. Mystery solved!




1 comment:

  1. haha!!that was nice!hey i'm a medical student and i found this page,while i was searching for info about extraocular muscles for my confrence!and let me tell u the info was helpful,thnx alot!its funny why some people dont see the obvious things?!its my email:longjohnsilver1001@yahoo.com

    ReplyDelete

LinkWithin

Related Posts Plugin for WordPress, Blogger...