Which structure controls the size of the pupil and the amount of light entering the eye?

Which structure controls the size of the pupil and the amount of light entering the eye?

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

Answer: (C)

The iris. It’s the coloured ring around the pupil that can change the size of the opening (the pupil) to control how much light enters the eye. Two muscle sets inside the iris work in opposition: the circular muscles constrict the pupil in bright light, reducing light entry, while the radial muscles dilate the pupil in dim light, letting in more light. This regulation helps protect the retina from excessive light and optimizes vision. Other parts have different jobs. The cornea and lens focus light onto the retina, and the retina detects that light to create vision. But the iris is the structure that directly adjusts how much light reaches the retina by changing pupil size.

The iris. It’s the coloured ring around the pupil that can change the size of the opening (the pupil) to control how much light enters the eye. Two muscle sets inside the iris work in opposition: the circular muscles constrict the pupil in bright light, reducing light entry, while the radial muscles dilate the pupil in dim light, letting in more light. This regulation helps protect the retina from excessive light and optimizes vision.

Other parts have different jobs. The cornea and lens focus light onto the retina, and the retina detects that light to create vision. But the iris is the structure that directly adjusts how much light reaches the retina by changing pupil size.