Discuss the function of iris.

Explanation

### Step-by-Step Solution:

1. **Definition of Iris**: The iris is the visible colored part of the eye. It is the portion that surrounds the pupil and is responsible for the eye's color.

2. **Function of the Iris**: The primary function of the iris is to control the amount of light that enters the eye. It does this by adjusting the size of the pupil, which is the opening in the center of the iris.

3. **Mechanism of Action**:
- When there is bright light, the iris constricts (makes the pupil smaller) to reduce the amount of light entering the eye. This helps protect the retina from excessive light exposure.
...