In the consensual pupillary light reflex, the pupil of the opposite eye constricts when light is shone in one eye.

In the consensual pupillary light reflex, the pupil of the opposite eye constricts when light is shone in one eye.

• A. Shining light in one eye causes constriction in the opposite pupil.
• B. Shining light in one eye causes constriction in the same eye.
• C. Shining light in one eye causes dilation in the opposite pupil.
• D. Shining light in one eye causes dilation in the same eye.

Answer: (A)

Consensual pupillary light reflex happens because both pupils receive the same parasympathetic signal when light hits one eye. The light signal travels from the retina to the brainstem and activates a pathway that projects to both Edinger–Westphal nuclei. From there, parasympathetic fibers travel with the oculomotor nerve to the sphincter pupillae in both eyes, causing constriction. So, when light is shone in one eye, the illuminated eye constricts (direct reflex) and the opposite eye also constricts (consensual reflex). The opposite pupil constricts because the neural circuit drives both eyes simultaneously.

Consensual pupillary light reflex happens because both pupils receive the same parasympathetic signal when light hits one eye. The light signal travels from the retina to the brainstem and activates a pathway that projects to both Edinger–Westphal nuclei. From there, parasympathetic fibers travel with the oculomotor nerve to the sphincter pupillae in both eyes, causing constriction. So, when light is shone in one eye, the illuminated eye constricts (direct reflex) and the opposite eye also constricts (consensual reflex). The opposite pupil constricts because the neural circuit drives both eyes simultaneously.