Question:medium
Look at the eye movement shown in the image. The movement is lost in:
Look at the eye movement shown in the image. The movement is lost in:
Show Hint
Which single muscle depresses and intorts the eye, and which nerve drives it?
Updated On: Jun 23, 2026
- Third nerve palsy
- Trochlear palsy
- Sixth nerve palsy
- Facial nerve palsy
Show Solution
The Correct Option is B
Solution and Explanation
Clinical pearl: CN IV = superior oblique = SO4 (Superior Oblique is supplied by cranial nerve 4). The superior oblique intorts and depresses the eye, and depression is strongest when the eye is adducted. A defect in this exact movement points straight to the trochlear nerve.
Quick elimination: the third nerve runs most extraocular muscles and the lid, so its palsy gives ptosis and a down-and-out dilated-pupil eye, not an isolated movement loss. The sixth nerve is lateral rectus only, so failure shows up as loss of abduction. The facial nerve has nothing to do with eyeball movement; it moves the muscles of facial expression and closes the lids.
Remember the unique trochlear trivia, which examiners love: smallest cranial nerve, longest intracranial path, and the only one leaving the brainstem from the back (dorsal exit). It comes from the midbrain and curves forward to the superior oblique. Putting the muscle action together with these features makes trochlear palsy the answer.
Quick elimination: the third nerve runs most extraocular muscles and the lid, so its palsy gives ptosis and a down-and-out dilated-pupil eye, not an isolated movement loss. The sixth nerve is lateral rectus only, so failure shows up as loss of abduction. The facial nerve has nothing to do with eyeball movement; it moves the muscles of facial expression and closes the lids.
Remember the unique trochlear trivia, which examiners love: smallest cranial nerve, longest intracranial path, and the only one leaving the brainstem from the back (dorsal exit). It comes from the midbrain and curves forward to the superior oblique. Putting the muscle action together with these features makes trochlear palsy the answer.
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