Pupil reflex receptors in the retina

Steps:

• Identify the pupil reflex as the pupillary light reflex, triggered by light detection.
• Recall that light enters the eye and stimulates photoreceptors to initiate the reflex arc.
• Locate photoreceptors (rods and cones) in the retina, the innermost eye layer.
• Confirm the reflex pathway: retina signals optic nerve to brain, then to ciliary ganglion for pupil constriction.

Why D is correct:

• The retina contains rods and cones, the photoreceptors that detect light intensity changes, directly initiating the pupil reflex per standard neuroanatomy.

Why the others are wrong:

• A: Cornea refracts light but has no sensory receptors for reflexes.
• B: Lens focuses light without detecting it or housing reflex receptors.
• C: Iris controls pupil size via muscles but does not sense light.

Final answer: D