Final answer:
The swinging flashlight test is used to assess afferent pupillary defects by comparing the pupillary reactions in each eye to a light stimulus, looking for any asymmetry indicating a defect in the sensory input through the optic nerve.
Step-by-step explanation:
A test used to evaluate afferent pupillary defects, such as the relative afferent pupillary defect, is the swinging flashlight test. During this test, a light is shone into each eye individually while observing the pupillary response. If the pupils constrict less when the light is in the affected eye compared to the healthy eye, it indicates an afferent pupillary defect.
This test helps differentiate whether a visual defect is due to ocular pathology or damage to the optical pathways leading up to the visual cortex. To perform the test, the examiner swings the light back and forth between the two eyes in a dark room and compares the direct and consensual reflexes. The normal response would be equal constriction of both pupils irrespective of which eye is stimulated. A defect is present if the eye with a sensory loss shows a weaker or absent reaction.
In the context of pupillary reflexes, the optic nerve serves as the afferent branch bringing signals to the brain, while the oculomotor nerve carries the motor response back to the iris' circular fibers, enabling the pupil to constrict or dilate.