Which defect of the eye can be corrected using a cylindrical lens ?

Explanation

### Step-by-Step Solution:

1. **Identify the Eye Defects**: The human eye can have various defects such as myopia (nearsightedness), hypermetropia (farsightedness), and astigmatism. Each of these defects has specific characteristics and requires different types of lenses for correction.

2. **Understand Astigmatism**: Among these defects, astigmatism is characterized by the inability to see straight lines clearly. This occurs because the cornea is not perfectly spherical, leading to distorted vision where straight lines appear curved.

3. **Role of Cylindrical Lenses**: To correct astigmatism, cylindrical lenses are used. These lenses are designed to focus light differently in one direction compared to the other, compensating for the irregular shape of the cornea and allowing for clearer vision of straight lines.

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