**Myopia** or **short-sightedness** is when a person can see **near objects clearly**, but **distant objects appear blurred**.
**Concave lenses** diverge light rays and are used to correct **myopia**.
In **hypermetropia** (farsightedness), light rays focus **behind the retina**.
**Convex lenses** converge light rays and help form the image on the retina in **hypermetropic** eyes.
**Presbyopia** is an **age-related** defect where the **eye loses its ability to accommodate**, making it hard to focus on both near and distant objects.
**Astigmatism** occurs due to **uneven curvature** of the cornea/lens, causing blurred or distorted vision.
**Cylindrical lenses** are used to correct **astigmatism** by compensating for the uneven curvature of the eye.