Which structure is a ring of muscle that controls the size of the pupil?

Which structure is a ring of muscle that controls the size of the pupil?

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

Answer: (C)

The size of the pupil is controlled by muscles in the iris, which forms a ring around the pupil. The iris contains two smooth muscle groups: circular fibres that contract to make the pupil smaller in bright light, and radial fibres that contract to enlarge the pupil in dim light. This arrangement lets the iris adjust how much light enters the eye. The opening itself is the pupil, not a muscle. The cornea is the clear front surface that helps focus light, and the lens behind the iris changes shape to focus, but neither is the ring of muscle controlling pupil size.

The size of the pupil is controlled by muscles in the iris, which forms a ring around the pupil. The iris contains two smooth muscle groups: circular fibres that contract to make the pupil smaller in bright light, and radial fibres that contract to enlarge the pupil in dim light. This arrangement lets the iris adjust how much light enters the eye. The opening itself is the pupil, not a muscle. The cornea is the clear front surface that helps focus light, and the lens behind the iris changes shape to focus, but neither is the ring of muscle controlling pupil size.