Why do pupils dilate in darkness?

Answer: Allow more light to enter

Darkness makes muscles relax — Wrong. The dilator muscle does contract (radial muscles) while sphincter relaxes, but the purpose is letting in more light for vision.

Protect retina from damage — Wrong. Protection happens in bright light (pupils constrict). In darkness, pupils dilate (open wide) to capture more light for the retina.

Allow more light to enter ✓ — Correct! The iris controls pupil size. In darkness, radial muscles contract, opening the pupil wide (dilation) to allow maximum light to reach the retina. In bright light, circular muscles contract, shrinking the pupil (constriction) to prevent overexposure and protect photoreceptors. It's automatic light regulation for best vision!