A vitamin required for maintaining good eyesight.

Explanation

### Step-by-Step Text Solution:

1. **Identify the Vitamin**: The question asks for a vitamin that is essential for maintaining good eyesight. The vitamin that plays a crucial role in this function is Vitamin A.

2. **Understand the Role of Vitamin A**: Vitamin A is important for the health of the retina in the eyes, which is necessary for seeing clearly, especially in low light conditions.

3. **Effects of Deficiency**: A deficiency in Vitamin A can lead to a condition known as night blindness, where a person has difficulty seeing in dim light or darkness.

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