What is myopia and what causes it?

Myopia is short sight, in which distant objects appear blurred because the eyeball is too long or the eye's own lens is too powerful, so light from a distant object is brought to a focus in front of the retina.

What is meant by the far point of an eye?

The far point is the greatest distance at which the eye can see an object clearly with the eye relaxed, and for a normal eye it is at infinity.

What type of lens corrects myopia and how does it work?

A diverging lens is used, and it forms a virtual image of a distant object at the eye's own far point, from which the eye can then focus the light onto the retina.

What is hypermetropia and what causes it?

Hypermetropia is long sight, in which near objects appear blurred because the eyeball is too short or the eye's lens is too weak, so light from a close object would be brought to a focus behind the retina.

What is meant by the near point of an eye?

The near point is the closest distance at which an object can be seen clearly with the eye fully accommodated, and for a normal eye it is taken as 0.25 m.

What type of lens corrects hypermetropia and how does it work?

A converging lens is used, and it forms a virtual image at the eye's own near point of an object placed closer than that, so the eye can focus on something at a comfortable reading distance.

CCEA A-Level Physics 1210

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Lenses

Correcting myopia and hypermetropia

3 things to know
Unit AS 2

Overview

Myopia and what causes it, far point of an eye and lens corrects myopia and how does it work.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

A short-sighted person has a far point of 0.50 m. Calculate the power of the correcting lens.

Numbers

A long-sighted person has a near point of 1.00 m and wishes to read at 0.25 m. Calculate the power of the correcting lens.

Key term

Explain why the power of a lens prescribed for myopia is negative while that prescribed for hypermetropia is positive.

Questions from this subtopic

Each one with the model answer underneath.

1
What is myopia and what causes it?
Model answer
Myopia is short sight, in which distant objects appear blurred because the eyeball is too long or the eye's own lens is too powerful, so light from a distant object is brought to a focus in front of the retina.
2
What is meant by the far point of an eye?
Model answer
The far point is the greatest distance at which the eye can see an object clearly with the eye relaxed, and for a normal eye it is at infinity.
3
What type of lens corrects myopia and how does it work?
Model answer
A diverging lens is used, and it forms a virtual image of a distant object at the eye's own far point, from which the eye can then focus the light onto the retina.
4
What is hypermetropia and what causes it?
Model answer
Hypermetropia is long sight, in which near objects appear blurred because the eyeball is too short or the eye's lens is too weak, so light from a close object would be brought to a focus behind the retina.
5
What is meant by the near point of an eye?
Model answer
The near point is the closest distance at which an object can be seen clearly with the eye fully accommodated, and for a normal eye it is taken as 0.25 m.
6
What type of lens corrects hypermetropia and how does it work?
Model answer
A converging lens is used, and it forms a virtual image at the eye's own near point of an object placed closer than that, so the eye can focus on something at a comfortable reading distance.

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