The primary action of the superior oblique occurs when it is positioned __ degrees medial to the line of sight.

• A. 50 degrees
• B. 60 degrees
• C. 54 degrees
• D. 52 degrees

Answer: (C)

When the eye is turned inward by about 54 degrees, the pull of the superior oblique aligns most strongly with rotating the top of the eye toward the nose. This is the position where its torsional effect—intorsion—dominates the muscle’s action, so intorsion becomes the primary action. The superior oblique is known to intort the eye as its main action, with depression as its secondary action when the eye is adducted and abduction as a tertiary action. The 54-degree adduction angle is the textbook point at which that primary torsional effect is observed, which is why this option is correct. The other angles don’t correspond to the gaze where intorsion is the dominant action.