Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the main effect of oculomotor nerve palsy?

1. Loss of sensation in the face

2. Drooping eyelid and fixed, dilated pupil

3. Loss of muscle coordination

4. Numbness in the extremities

The correct answer is: Drooping eyelid and fixed, dilated pupil

The main effect of oculomotor nerve palsy is reflected in the physical presentation characterized by a drooping eyelid (ptosis) and a fixed, dilated pupil (mydriasis). This condition arises from dysfunction of the oculomotor nerve, which is responsible for controlling most of the eye's movements, as well as the constriction of the pupil and maintaining the position of the eyelid. When there is a palsy of the oculomotor nerve, the muscles that the nerve innervates become weak or paralyzed. This results in a noticeable drooping of the upper eyelid because the levator palpebrae superioris muscle, which elevates the eyelid, is affected. Additionally, the inability of the pupil to constrict reflects an impairment in the parasympathetic function of the oculomotor nerve, leading to pupillary dilation and an unresponsive state. This distinct combination of symptoms is essential to identify oculomotor nerve palsy, which can aid in diagnosing the underlying causes such as an aneurysm, trauma, or other neurological conditions. Understanding these specific clinical features helps elucidate the nature of the nerve impairment and provides vital information for appropriate management and treatment.