A person is not able to see vertical wires clearly in a grid of wires. What is this defect and how it is corrected ?

Explanation

### Step-by-Step Solution

1. **Identify the Defect**:
The person is unable to see vertical wires clearly in a grid of wires. This indicates a visual impairment related to the perception of vertical lines.

2. **Define the Condition**:
The condition described is known as **astigmatism**. It is a common refractive error caused by an irregular shape of the cornea or lens, which leads to blurred or distorted vision.

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