Which of the following will NOT cause an afferent pupillary defect (APD)?

• A. Dense vitreous hemorrhage
• B. Retinal detachment
• C. Occipital lobe stroke
• D. Glaucoma

Answer: (C)

The question hinges on the afferent limb of the pupillary light reflex. A pupil reacts to light only if the retinal signal can reach the pretectal area and Edinger–Westphal nuclei to drive constriction. Dense opacity in the eye, like a dense vitreous hemorrhage, blocks light from reaching the retina, so the signal is diminished and an afferent defect appears. A retinal detachment disrupts retinal function, weakening the incoming signal to the optic nerve and likewise producing an APD. Glaucoma damages the optic nerve itself, reducing the afferent input to the reflex arc and leading to an APD.

An occipital lobe stroke is a cortical lesion after the optic pathways have already carried the signal to the visual cortex. The pupillary light reflex relies on subcortical circuits, so cortical vision loss from an occipital stroke does not typically produce an APD. Thus, the occipital lobe stroke will not cause an afferent pupillary defect.