Superior oblique muscle performs action of -a) Intortionb) Extortion c) Elevationd) Medial rotation
The primary action of superior oblique muscle is intorsion.The subsidiary actions are depression and abduction.
Dont get confuse by option d. Intorsion is also called medial rotation or internal rotation and extorsion is also called lateral rotation or external rotation.

Note:-
Khurana has mentioned medial rotation as adduction and lateral rotation as abduction. This is incorrect. I have checked it from various standard textbook of ophthalmology and also from internet. If you dont believe, read following statments:-
"Superior rectus causes elevation (upward movement), adduction and intorsion (medial rotation) of the eye".— Clinical ophthalmology
"Contraction of superior oblique muscle causes depression, medial rotation and abduction". — Oswald steward
"The rolling movement of eye towards the nose is called intorsion or medial rotation while rolling movement away from nose is called extorsion or lateral rotation".  — Textbook of practical physiology
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