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Hypermetropia

Hypermetropia is a defect in which a person sees distant objects clearly but nearby objects appear blurred.

In one line: Hypermetropia means far clear, near blurred.

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Understand it

In hypermetropia, light from a nearby object is focused behind the retina instead of on it. This may happen because the eyeball is too short or the eye lens has too little converging power. A convex lens is used for correction because it helps the eye converge the rays earlier.

Example

An elder person may see the classroom board well but need to hold a newspaper farther away to read comfortably.

Formula and rule

Hypermetropia correction uses a convex lens of suitable focal length to increase the eye's converging power.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1If a person cannot read clearly at 25 cm but can read at 40 cm, the near point is too far.
  2. 2A convex lens is prescribed so the image of a near object forms on the retina.

Method you can reuse

  1. 1State that distant objects are clear and nearby objects are blurred.
  2. 2Mention that the image forms behind the retina.
  3. 3Give causes like short eyeball or weak converging power.
  4. 4State that a convex lens is used.
  5. 5Explain that it converges rays before they enter the eye.

Sketch it in your answer

Draw a hypermetropic eye with rays from a near object focusing behind the retina, then show a convex lens moving the image onto the retina.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does a convex lens help a hypermetropic eye see nearby objects clearly?

Think first, then show answer
A convex lens converges the light rays before they enter the eye, so the image of a nearby object is shifted onto the retina. This corrects the blurred near vision of hypermetropia.

Common wrong answer

A common wrong answer is to use a concave lens.

Why it loses marks: A concave lens would diverge rays further and worsen near vision.

Don't mix this up

Students often reverse myopia and hypermetropia and choose the wrong corrective lens.

Exam tip

For hypermetropia, always mention behind the retina and the use of a convex lens.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Explain the defect and its correction, or identify the lens in a case where nearby reading is difficult.
  1. 1

    Enough for 1 mark

    Hypermetropia is a defect in which a person sees distant objects clearly but nearby objects appear blurred.

  2. 2

    Add for 2 marks

    In hypermetropia, light from a nearby object is focused behind the retina instead of on it.

  3. 3

    Add for 3 marks

    This may happen because the eyeball is too short or the eye lens has too little converging power.

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