If the source of light in front of eye suddenly become bright :

Options

A. Pupil of eye contracts
B. Focus of lens changes
C. Vitreous humor becomes liquid-like
D. Retina blood supply is cut - off

Answer

**Step-by-Step Solution:**

1. **Understanding the Situation**: When a bright light source suddenly appears in front of the eyes, the eyes need to adjust to prevent excessive light from entering.

2. **Role of the Pupil**: The pupil is the opening in the center of the iris that regulates the amount of light entering the eye. In response to bright light, the pupil constricts (gets smaller) to limit the amount of light that can enter.

3. **Evaluating the Options**:
- **Option 1**: "Pupil of eye contracts" - This is the correct answer. The pupil constricts to protect the retina from damage due to excessive light.
- **Option 2**: "Focus on the lens changes" - This option is incorrect. The lens focuses light but does not change its focus in direct response to brightness.
- **Option 3**: "Vitreous humor becomes liquid-like" - This option is also incorrect. The vitreous humor does not change its state in response to light intensity.
- **Option 4**: "Retinal blood supply is cut off" - This option is incorrect as well. The retinal blood supply is not affected by sudden changes in light intensity.

4. **Conclusion**: The correct response to a sudden increase in brightness is that the pupil of the eye contracts to reduce light entry.

**Final Answer**: The pupil of the eye contracts.

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