What is a common sign of oculomotor nerve (CNIII) paralysis?

A common sign of oculomotor nerve (CN III) paralysis is indeed a unilateral dilated and fixed pupil. When the oculomotor nerve is affected, it leads to impaired control over several functions of the eye, including the constrictor muscles of the iris. As a result, the pupil on the side where the nerve is paralyzed fails to constrict in response to light or accommodation, leading to a dilated state. This can be particularly evident when assessing pupil reactions under different lighting conditions.

In addition, this condition can be accompanied by other signs such as ptosis (drooping of the eyelid) and an outwardly turned eye due to unopposed action of the lateral rectus muscle (which is innervated by the abducens nerve). Therefore, the observation of a unilateral dilated and fixed pupil is a critical clinical sign that indicates potential oculomotor nerve involvement and necessitates further evaluation of the patient's neurological status.