Damage to which cranial nerve would most likely cause medial strabismus due to unopposed medial rectus action?

Damage to which cranial nerve would most likely cause medial strabismus due to unopposed medial rectus action?

• A. Oculomotor nerve
• B. Abducens nerve
• C. Trochlear nerve
• D. Trigeminal nerve

Answer: (B)

When the eye’s position is considered, the balance between eye muscles that pull inward and outward determines where the eye rests. The medial rectus tugs the eye toward the nose, while the lateral rectus pulls it outward. If the nerve that powers the lateral rectus (the abducens nerve) is damaged, the lateral rectus can no longer abduct the eye. With the lateral rectus out of commission, the medial rectus acts unopposed and shifts the eye inward, producing medial strabismus. Damage to the oculomotor nerve would weaken the medial rectus among other muscles, usually causing the eye to rest outward rather than inward. Trochlear nerve injury affects the superior oblique, leading to vertical misalignment and diplopia with gaze downward. The trigeminal nerve isn’t responsible for controlling these eye movements.

When the eye’s position is considered, the balance between eye muscles that pull inward and outward determines where the eye rests. The medial rectus tugs the eye toward the nose, while the lateral rectus pulls it outward. If the nerve that powers the lateral rectus (the abducens nerve) is damaged, the lateral rectus can no longer abduct the eye. With the lateral rectus out of commission, the medial rectus acts unopposed and shifts the eye inward, producing medial strabismus.

Damage to the oculomotor nerve would weaken the medial rectus among other muscles, usually causing the eye to rest outward rather than inward. Trochlear nerve injury affects the superior oblique, leading to vertical misalignment and diplopia with gaze downward. The trigeminal nerve isn’t responsible for controlling these eye movements.