Question

The size of pupil decreases due to the contraction of

• A. Radial muscles
• B. Circular muscles
• C. Both circular and radial muscles
• D. Nictiating membrane

Answer 1

Answer: (B)

Circular muscles

Pupil is an aperture in the eye through which light rays enter the eye. The amount of light entering the eye is regulated by iris which controls the size of pupil. Iris consists of two types of smooth muscles, circular muscles and radial muscles. Circular muscles are called sphincter pupillae and radial muscles are called dilator pupillae. The size of pupil decreases when sphincter pupillae or circular muscles contract and increases when dilator pupillae or radial muscles contract.

So, the correct answer is 'Circular muscles'.