Which part of the eye adjusts pupil size to regulate light intake?

• A. Retina
• B. Iris
• C. Lens
• D. Pupil

Answer: (B)

The iris is the part that adjusts pupil size. It contains smooth muscle that acts like a camera diaphragm to change the diameter of the pupil, the opening in the center of the iris. In bright light, the circular muscles contract to make the pupil smaller, limiting light and protecting the retina. In dim light, the radial muscles pull the pupil open, allowing more light in. The pupil itself is just the opening; it doesn’t actively adjust on its own. The retina detects light, and the lens helps focus it, but the iris is what regulates how much light enters the eye.