Question

Explain Myopia and Hypermetropia with their causes and correction methods.

Hint:

Myopia causes difficulty in seeing distant objects and is corrected with a concave lens, while hypermetropia causes difficulty in seeing near objects and is corrected with a convex lens.

Answer 1

Concept: Defects of vision occur when the eye is unable to focus light properly on the retina. Two common defects of vision are Myopia (short-sightedness) and Hypermetropia (long-sightedness). These defects arise due to changes in the shape of the eyeball or the focal length of the eye lens and can be corrected using suitable lenses.
Step 1:Myopia (Short-sightedness).
Myopia is a defect of vision in which a person can see near objects clearly but distant objects appear blurred. Cause:

• The eyeball becomes elongated, or
• The focal length of the eye lens becomes too small.

Because of this, the image of distant objects is formed in front of the retina instead of on the retina. Correction:

• Myopia is corrected using a concave (diverging) lens.
• The concave lens diverges the incoming light rays so that the image is formed exactly on the retina.

Step 2:Hypermetropia (Long-sightedness).
Hypermetropia is a defect of vision in which a person can see distant objects clearly but near objects appear blurred. Cause:

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

As a result, the image of nearby objects is formed behind the retina. Correction:

• Hypermetropia is corrected using a convex (converging) lens.
• The convex lens converges the light rays so that the image is formed on the retina.

Step 3:Difference between Myopia and Hypermetropia.

• Vision: Myopia affects distant vision, while hypermetropia affects near vision.
• Image formation: In myopia, the image forms in front of the retina, whereas in hypermetropia the image forms behind the retina.
• Corrective lens: Myopia is corrected with a concave lens, while hypermetropia is corrected with a convex lens.