How does the eye adjust to take account of an increase in brightness ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Structure of the Eye**:
- The human eye consists of several parts, including the cornea, iris, pupil, and retina. The cornea is the clear front layer, the iris is the colored part of the eye, and the pupil is the black circular opening in the center of the iris.

2. **Role of the Iris**:
- The iris plays a crucial role in controlling the amount of light that enters the eye. It adjusts the size of the pupil, which is the opening through which light passes.

3. **Response to Brightness**:
- When there is an increase in brightness, such as when stepping into bright sunlight, the iris responds by constricting (making the pupil smaller). This reduces the amount of light that enters the eye.

4. **Protecting the Retina**:
- The retina is sensitive to light and can be damaged by excessive brightness. By constricting the pupil, the iris ensures that only a safe amount of light reaches the retina, protecting it from potential damage.

5. **Conclusion**:
- In summary, the eye adjusts to increased brightness primarily through the action of the iris, which regulates the size of the pupil to control the amount of light entering the eye.