The swinging flashlight test assesses the pupillary light reflex by comparing the direct and consensual constriction of the pupils when a light is shone alternately into each eye. It is primarily used to detect a relative afferent pupillary defect (RAPD), indicating an optic nerve or severe retinal disease on the affected side. The test evaluates the integrity of the afferent limb (optic nerve) and efferent limb (oculomotor nerve) of the reflex arc. A normal response shows equal pupillary constriction; asymmetry during the test suggests pathology. This makes the swinging flashlight test crucial in neurological and ophthalmological examinations for visual pathway lesions.

Reference: Clinical Neuroanatomy, Richard S. Snell, 7th Edition.