Question

Explain the causes and correction methods for Myopia (Short-sightedness) and Hypermetropia (Long-sightedness).

Hint:

{Myopia → Corrected by Concave Lens}
{Hypermetropia → Corrected by Convex Lens}

Answer 1

Concept: Defects of vision occur when the eye is unable to focus light properly on the retina. Two common defects are Myopia (short-sightedness) and Hypermetropia (long-sightedness).
Step 1:Myopia (Short-sightedness)} Definition: Myopia is a defect of vision in which a person can see near objects clearly but distant objects appear blurred. Causes:

• The eyeball becomes elongated.
• The focal length of the eye lens becomes too short.

As a result, light rays from distant objects focus in front of the retina instead of on it. Correction: Myopia is corrected by using a concave lens (diverging lens) which diverges the incoming light rays so that the image forms on the retina.
Step 2:Hypermetropia (Long-sightedness)} Definition: Hypermetropia is a defect of vision in which a person can see distant objects clearly but near objects appear blurred. Causes:

• The eyeball becomes shorter than normal.
• The focal length of the eye lens becomes too large.

Therefore, light rays from nearby objects focus behind the retina instead of on it. Correction: Hypermetropia is corrected by using a convex lens (converging lens) which converges the light rays before they enter the eye so that the image forms on the retina.