What opening in the eye regulates light entering by changing size?

What opening in the eye regulates light entering by changing size?

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

Answer: (D)

Light entering the eye is controlled by the pupil, an opening whose size changes to regulate how much light reaches the retina. The iris—the colored ring around the pupil—adjusts that opening using its two muscle groups to constrict or dilate. In bright light, the pupil narrows to limit light and protect the retina; in dim light, it widens to let in more light. The lens behind the pupil focuses light onto the retina, while the cornea at the front refracts light. So the opening that changes size to control light entering the eye is the pupil.

Light entering the eye is controlled by the pupil, an opening whose size changes to regulate how much light reaches the retina. The iris—the colored ring around the pupil—adjusts that opening using its two muscle groups to constrict or dilate. In bright light, the pupil narrows to limit light and protect the retina; in dim light, it widens to let in more light. The lens behind the pupil focuses light onto the retina, while the cornea at the front refracts light. So the opening that changes size to control light entering the eye is the pupil.