Final answer:
To assess the consensual pupillary reflex, you should shine light into one eye and observe both pupils for constriction. This reflex is a crucial diagnostic tool for identifying potential damage to the optic or oculomotor nerves.
Step-by-step explanation:
To assess the consensual pupillary reflex, Option 1: Shine light into one eye and observe both pupils is the correct method. When the light is shone in one eye, you should note the constriction of that pupil as well as the constriction of the contralateral pupil. This occurs because the afferent limb of the pupillary light reflex, which begins when light hits the retina and signals travel along the optic nerve, is shared by both eyes. The corresponding motor response through the oculomotor nerve sends signals to the ciliary ganglion, which then stimulates the circular fibers of the iris, resulting in constriction of both pupils. If the light response is only seen in the eye that is not directly illuminated, this indicates that the consensual reflex is intact, pointing to a possible issue with the oculomotor nerve or Edinger-Westphal nucleus on the side where the light was shone.