Final answer:
When a flashlight is shined into your eye, both pupils constrict due to the pupillary light reflex, which can be used to diagnose nerve damage.
Step-by-step explanation:
If someone shined a flashlight into your eye, your pupils would constrict. The pupillary light reflex involves a sensory input through the optic nerve (the afferent limb) and a motor response through the oculomotor nerve (the efferent limb) to the ciliary ganglion, which signals the circular fibers of the iris to constrict. This bilateral response means that if a flashlight is shone into one eye, both eyes will experience pupil constriction. Shine a flashlight in just one eye, and that eye will undergo a direct reflex, while the other eye will exhibit what is known as the consensual reflex. This response serves to protect the retina by controlling the amount of light hitting it. Also, medical professionals use this reaction to check for damage to either the optic or the oculomotor nerves. Abnormalities in the reflex can indicate potential nerve damage, which is significant in diagnosing various neurological conditions.