Final answer:
Assessing a patient's pupil constriction with a bright light helps determine the functionality of the cranial nerve responsible for this reflex, which is the oculomotor nerve (cranial nerve III).
Step-by-step explanation:
Assessing a patient's pupil constriction with a bright light helps determine the functionality of the cranial nerve responsible for this reflex. In this case, the cranial nerve being assessed is the oculomotor nerve (also known as cranial nerve III). This nerve controls the constriction of the pupils in response to light exposure. If shining a light in one eye results in no changes in pupillary size but shining light in the opposite eye elicits a normal, bilateral response, it suggests damage to the optic nerve on the nonresponsive side. On the other hand, if light in either eye elicits a response in only one eye, it indicates a problem with the oculomotor system.