A light is directed at a patient's pupil, which contracts. It is also noted that the other pupil contracts as well, though it is not exposed to bright light. Which term describes this phenomenon?

A. Direct reaction is incorrect because the direct pupillary light reflex refers specifically to the constriction of the pupil that is directly exposed to light. It does not describe the behavior of the opposite pupil, which is responding indirectly. Assessing the direct reaction helps evaluate the function of the afferent pathway (optic nerve, CN II) and the efferent pathway (oculomotor nerve, CN III) of the illuminated eye. B. Consensual reaction is correct because the consensual pupillary light reflex describes the simultaneous constriction of the pupil opposite to the one being directly stimulated by light. When light enters one eye, afferent signals travel via the optic nerve (CN II) to the pretectal nuclei in the midbrain, which then communicate bilaterally with the Edinger-Westphal nuclei. Efferent signals are sent via the oculomotor nerves (CN III) to both pupils, resulting in constriction of both the directly exposed pupil and the contralateral pupil. The consensual reflex demonstrates bilateral integrity of the optic and oculomotor pathways, even when only one eye is exposed to light. C. Near reaction is incorrect because it refers to pupillary constriction that occurs when the eyes focus on a near object, as part of the accommodation reflex, and is not triggered by light. It is primarily a test of focusing ability rather than pupillary light response. D. Accommodation is incorrect because it involves a triad of responses—pupillary constriction, lens thickening, and convergence of the eyes—when shifting focus from a distant to a near object. While pupillary constriction occurs, it is not in response to light and therefore is distinct from the consensual light reflex.