Which of the following regulates the amount of light entering the eye?

Options

A. Lens
B. Ciliary body
C. Iris
D. Aqueous humor

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks which part of the eye regulates the amount of light entering it. The options provided are lens, ciliary body, iris, and aqueous humor.

2. **Identifying the Function of Each Option:**
- **Lens:** The lens is responsible for focusing light onto the retina to create a clear image.
- **Ciliary Body:** The ciliary body helps in changing the shape of the lens for focusing on objects at different distances.
- **Aqueous Humor:** This is the fluid in the front part of the eye that provides nutrients and maintains intraocular pressure.
- **Iris:** The iris is a ring-like structure that surrounds the pupil and controls the size of the pupil.

3. **Focusing on the Iris:**
The iris is the part of the eye that regulates the amount of light entering through the pupil. It can expand or contract:
- In bright light, the iris relaxes, causing the pupil to constrict (become smaller) to reduce the amount of light entering the eye.
- In dim light, the iris contracts, allowing the pupil to dilate (become larger) to let more light in.

4. **Conclusion:**
Based on the functions of each part of the eye, the correct answer to the question is the **iris**, as it directly controls the amount of light that enters the eye.

**Final Answer:**
The part of the eye that regulates the amount of light entering is the **iris**.

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