In the pupillary light reflex, the afferent limb carries information from which structure?

• A. Retina
• B. Lateral geniculate nucleus
• C. Visual cortex
• D. Efferent pathways to the iris

Answer: (A)

Light detection by photoreceptors in the retina starts the pupillary light reflex, so the afferent limb is the retinal signal. This information travels through the optic nerve to the pretectal area of the midbrain and then bilaterally to the Edinger–Westphal nucleus, which sends parasympathetic signals via the oculomotor nerve to the iris sphincter, causing constriction. The retina is the source of the afferent input, making it the best answer. The lateral geniculate nucleus and visual cortex belong to the conscious visual pathway and are not required for this reflex, while the efferent pathways to the iris carry the motor command rather than the sensory input.