Which is not a refractive medium of eye

Options

A. Lens
B. Vitreous humour
C. Aqueous humour
D. Pupil.

Answer

To determine which structure is not a refractive medium of the eye, we will analyze the options provided: lens, vitreous humor, aqueous humor, and pupil.

### Step-by-Step Solution:

1. **Understanding Refractive Mediums**:
- Refractive mediums are structures in the eye that help to bend (refract) light as it passes through them, allowing us to focus on objects at various distances.

2. **Identifying the Refractive Mediums**:
- **Cornea**: The clear outer layer of the eye that initially refracts light.
- **Aqueous Humor**: The fluid in the anterior chamber of the eye that also refracts light.
- **Lens**: A flexible structure that can change shape to focus light on the retina.
- **Vitreous Humor**: The gel-like substance filling the space between the lens and the retina, which also helps in light refraction.

3. **Analyzing the Options**:
- **Lens**: A refractive medium.
- **Vitreous Humor**: A refractive medium.
- **Aqueous Humor**: A refractive medium.
- **Pupil**: The opening that allows light to enter the eye but does not refract light.

4. **Conclusion**:
- The structure that is **not** a refractive medium of the eye is the **pupil**. The pupil merely regulates the amount of light entering the eye but does not bend or refract light.

### Final Answer:
The correct option is **pupil**.

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