Function of iris is to

Options

A. move lens forward and backward
B. refract light rays
C. bring about movements of eyelids
D. alter the size of pupil

Explanation

**Step-by-Step Solution:**

1. **Definition of Iris**: The iris is a thin, circular structure in the eye that surrounds the pupil. It is responsible for controlling the diameter and size of the pupil.

2. **Origin of the Term**: The term "iris" comes from the Latin word for rainbow, which reflects its various colors.

3. **Structure of the Iris**: The iris is an extension of the choroid layer of the eye and contains two types of muscles: radial muscles and circular muscles.

4. **Function of Muscles**:
- **Radial Muscles**: These muscles are responsible for widening the pupil (dilating the pupil). When they contract, the pupil enlarges, allowing more light to enter the eye.
- **Circular Muscles**: These muscles constrict the pupil (making it smaller). When they contract, the pupil shrinks, reducing the amount of light entering the eye.

5. **Regulation of Light**: The primary function of the iris is to adjust the size of the pupil, thereby regulating the amount of light that enters the eye. This is crucial for protecting the retina from excessive light and for improving vision under different lighting conditions.

6. **Conclusion**: Therefore, the function of the iris is to control the size of the pupil and regulate the amount of light entering the eye.

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