The opening in the iris that regulates the amount of light entering the eye.

The opening in the iris that regulates the amount of light entering the eye.

• A. Iris
• B. Choroid
• C. Optic nerve
• D. Pupil

Answer: (D)

Light entering the eye is controlled by the pupil, the opening in the iris. The iris is the colored part around the pupil and uses two sets of muscles to adjust this opening: the dilator muscles widen it in dim light to let more light in, while the sphincter muscles narrow it in bright light to reduce light. This adjustment helps protect the retina from glare and allows you to see in different lighting. The choroid is a vascular layer that supplies nutrients, and the optic nerve carries visual information to the brain, but neither controls this opening. So the opening through which light passes is the pupil.

Light entering the eye is controlled by the pupil, the opening in the iris. The iris is the colored part around the pupil and uses two sets of muscles to adjust this opening: the dilator muscles widen it in dim light to let more light in, while the sphincter muscles narrow it in bright light to reduce light. This adjustment helps protect the retina from glare and allows you to see in different lighting. The choroid is a vascular layer that supplies nutrients, and the optic nerve carries visual information to the brain, but neither controls this opening. So the opening through which light passes is the pupil.