The primary action of the superior rectus occurs when it is positioned __ degrees away from the midline.

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Prepare for the NBEO Ocular Motility Test. Practice with questions and explanations to enhance your understanding. Get ready for your exam easily!

Multiple Choice

The primary action of the superior rectus occurs when it is positioned __ degrees away from the midline.

Explanation:
The important idea is that a muscle’s action depends on where the eye is looking. The superior rectus mainly elevates the eye, and this elevating effect is most purely expressed when the eye is about 23 degrees away from the midline (in abduction). At roughly 23 degrees of gaze, the pull of the superior rectus aligns most with the vertical axis, so its vertical component (elevation) dominates and horizontal or torsional components are minimized. As you move the eye to other gaze angles, the muscle’s pull includes more of these other components, so elevation is not as purely the primary action. That’s why 23 degrees is the best answer.

The important idea is that a muscle’s action depends on where the eye is looking. The superior rectus mainly elevates the eye, and this elevating effect is most purely expressed when the eye is about 23 degrees away from the midline (in abduction). At roughly 23 degrees of gaze, the pull of the superior rectus aligns most with the vertical axis, so its vertical component (elevation) dominates and horizontal or torsional components are minimized. As you move the eye to other gaze angles, the muscle’s pull includes more of these other components, so elevation is not as purely the primary action. That’s why 23 degrees is the best answer.

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