What is indicated when the direct pupillary reflex is absent but the consensual reflex remains intact?

When the direct pupillary reflex is absent, but the consensual reflex remains intact, this indicates an afferent pupillary injury. The direct reflex is primarily mediated through the optic nerve (afferent pathway) and controls the constriction of the pupil in response to light entering the eye. When this reflex is absent, it suggests there is an issue with the ability of the affected eye to receive and process light stimuli.

The consensual reflex, on the other hand, refers to the reaction of the opposite eye to light shone in one eye, leading to both pupils constricting. If the consensual reflex is intact while the direct reflex is absent, it means that the efferent pathways (which control the muscles of the eye) are functioning normally in the other eye, allowing for constriction when light is introduced to either eye.

This scenario typically occurs in cases of unilateral retinal damage or optic nerve injury, where the affected eye cannot respond directly to light, but the pathways controlling the other eye's response remain intact. Thus, the presence of consensual reflex indicates that the neural pathways controlling the other eye's response are not impaired, while the absence of direct reflex points to an afferent (sensory) issue in the affected eye