What defining symptom would an impairment in cranial nerve VI likely cause?

An impairment in cranial nerve VI, also known as the abducens nerve, would typically lead to the eyes deviating inward. This nerve is primarily responsible for innervating the lateral rectus muscle, which is responsible for moving the eye laterally (outward). When cranial nerve VI is impaired, the affected eye often cannot move outward properly and tends to drift inward, leading to a condition known as esotropia.

The inward deviation of the eye occurs because the opposing muscles, particularly the medial rectus (innervated by cranial nerve III), overpower the lateral rectus muscle. This results in the inability to align both eyes for single binocular vision. Thus, the defining symptom of impairment in cranial nerve VI is indeed the inward deviation of the eyes. Understanding the specific role of cranial nerve VI in eye movement helps clarify why this finding is explicitly associated with its impairment.