What does an impairment of cranial nerve III typically cause?

An impairment of cranial nerve III, also known as the oculomotor nerve, typically results in the eye deviating down and out. This is due to the fact that cranial nerve III controls most of the eye's movements, including the ability to elevate and rotate the eye, as well as controlling the constriction of the pupil and maintaining an open eyelid.

When this nerve becomes impaired, the muscles it innervates are weakened or paralyzed, leading to unopposed action from the lateral rectus muscle, which is innervated by cranial nerve VI (abducens). This results in the affected eye being pulled laterally and slightly inferior. Consequently, the eye cannot properly align and appears deviated down and out when compared to the unaffected eye.

Understanding the function of cranial nerve III helps clarify this condition. The symptoms associated with its impairment can include ptosis (drooping eyelid) and mydriasis (dilated pupil), alongside the characteristic eye position.

The other choices do not accurately reflect the specific impact of cranial nerve III impairment. For example, photophobia relates more to issues with the retina or the optic nerve rather than the oculomotor nerve. Reduced color vision typically signals a