Question
Action of right superior oblique muscle is:
| A. |
Dextrodepression |
| B. |
Dextroelevation |
| C. |
Laevoelevation |
| D. |
Laevodepression |
|
Correct Answer » D Explanation |
 |
Detailed Explanation:
Anatomical Role:
– Superior oblique muscle: innervated by the trochlear nerve (cranial nerve IV).
– Primary actions: depression, abduction, and intorsion of the eyeball.
Clinical Reasoning for the Correct Answer:
– Right superior oblique → depresses the right eye most strongly when the eye is adducted (looking nasally/medially).
– In the right eye, “laevo” refers to left gaze (the patient’s left; observer’s right). “Depression” denotes movement downward.
– “Laevodepression”: moving the right eye downward while looking to the left (left-and-down gaze), which is the main field of action for the right superior oblique.
Why Option A is Incorrect:
– Dextrodepression: downward movement during right gaze.
– Controlled primarily by the right inferior rectus, not the superior oblique.
Why Option B is Incorrect:
– Dextroelevation: upward movement during right gaze.
– Controlled by the right superior rectus and left inferior oblique.
Why Option C is Incorrect:
– Laevoelevation: upward movement during left gaze.
– Controlled primarily by the right inferior oblique and left superior rectus.
Why Option D is Correct:
– Laevodepression: downward movement during left gaze (main field for right superior oblique).
– Superior oblique is most effective at depressing the eye in this position.
High‑Yield Synopsis:
– Extraocular Muscles – Primary Actions
– Superior oblique: depression, abduction, intorsion (especially when eye adducted).
– Inferior oblique: elevation, abduction, extorsion.
– Superior rectus: elevation, adduction, intorsion.
– Inferior rectus: depression, adduction, extorsion.
– Field of Action
– Superior/inferior recti: most effective when eye abducted.
– Obliques: most effective when eye adducted.
– Differential Movements
– Dextro- (right), laevo- (left): describe gaze direction relative to observer.
– Depression in laevo- (left gaze): right superior oblique main depressor.
– Elevation in dextro- (right gaze): right superior rectus main elevator.
– Nerve Supply
– Superior oblique: trochlear nerve (CN IV).
– All other extraocular muscles (except lateral rectus, abducens nerve) by oculomotor nerve (CN III).
