Q18
3 marksShort AnswerSection A

What eye defect is myopia ? Describe with a neat diagram how this defect of vision can be corrected by using a suitable lens.

The Human Eye and the Colourful World
Defects of Vision
Official Answer

Myopia, also known as near-sightedness, is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects distinctly. In a myopic eye, the image of a distant object is formed in front of the retina rather than on the retina itself.


Causes:

  1. Excessive curvature of the eye lens.
  2. Elongation of the eyeball.

Correction:

This defect is corrected by using a concave lens (diverging lens) of suitable power. The concave lens diverges the parallel rays from a distant object so that they appear to come from the far point of the myopic eye, eventually focusing the image exactly on the retina.



Near-sightednessIn front of retinaConcave lensDiverging lensElongation of eyeball

Marking Scheme

  • 1Definition of Myopia and its symptoms (1 mark)
  • 2Diagram showing image formation in front of retina and correction (1 mark)
  • 3Explanation of correction using concave lens (1 mark)

Hint

Think of 'Myopia' as 'Near-sighted'—you can see 'Near'. To fix it, you need a lens that spreads light out (concave).

Quick Oral Answer

Myopia is near-sightedness where distant objects look blurry because the image forms in front of the retina. It is corrected using a concave lens.

Analysis & Explanation

In Myopia, the eye's converging power is too high or the eyeball is too long. Consequently, rays from infinity converge too early. A concave lens provides the necessary divergence to counteract the eye's excess convergence, pushing the focal point back onto the retinal surface.

Common Mistakes

  1. 1Suggesting a convex lens for correction.
  2. 2Saying the image forms 'behind' the retina (that is hypermetropia).

Interesting Facts

The far point of a myopic eye is not at infinity; it is at a finite distance.

Spotted a mistake or something unclear?

Tell us — we fix reported answers fast.

Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2011?

This question carries 3 marks in the CBSE Class 10 Science 2011 examination.

Which chapter does this question come from in Science?

This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Defects of Vision" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2011 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.