Which EOM palsy would MOST likely result in an acute Esotropia?

• A. CN 3 palsy
• B. CN 4 palsy
• C. CN 5 palsy
• D. CN 6 palsy

Answer: (D)

This question hinges on what happens when the muscle that moves the eye outward is not working. The lateral rectus, which abducts the eye (moves it outward), is controlled by the sixth cranial nerve. When that nerve is impaired, the eye can’t abduct, and the unopposed action of the medial rectus pulls the eye inward. The result is an abrupt inward turning of the eye (acute esotropia) with horizontal double vision, especially noticeable when looking to the side of the affected muscle.

In contrast, a third-nerve (oculomotor) palsy typically leaves the eye abducted and resting down and out due to unopposed lateral rectus and superior oblique, producing exotropia and vertical misalignment rather than a primary inward deviation. A fourth-nerve (trochlear) palsy causes vertical diplopia with extorsion, not a horizontal inward turn. A trigeminal (fifth) nerve issue doesn’t produce a classic EOM palsy causing acute esotropia. So the acute esotropia best fits a sixth nerve (abducens) palsy.