B5 Correcting Vision Defects

Question 1

Complete the sentence

Long-sighted people are unable to focus on ……. objects.

Answer 1

Near

Question 2

Why can’t long sighted people focus on near objects?

Answer 2

This occurs when the lens is the wrong shape and doesn’t refract (bend) the light enough or the eyeball is too short.

Light rays don’t converge (meet at a point) on the retina, instead images of near objects are brought into focus behind the retina.

Question 3

What type of lens do glasses or contact lenses need to have to correct vision for someone who is long-sighted?

Answer 3

Convex lens

Question 4

What way does a convex lens curve and where is its fattest point?

Answer 4

Curves outwards, so its fattest in the centre.

Question 5

How does a convex lens help correct vision for long- sighted people?

Answer 5

The lens refracts light so it starts to converge before it enters the eye.

Question 6

What allows the image to be brought into focus for a long sighted person wearing convex lenses?

Answer 6

The increased convergence allows the image to be brought into focus on the retina.

Question 7

Why are older people often long-sighted?

Answer 7

As you get older, your eyes lens loses flexibility, so it can’t easily spring back into shape.

This means light can’t be focused well for near viewing.

Question 8

Complete the sentence

Short sighted people are unable to focus on ……….. objects.

Answer 8

Distant

Question 9

Why can’t short sighted people focus distant objects?

Answer 9

This occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long.

Light rays converge before they reach the retina, so images of distant objects are brought into focus in front of the retina.

Question 10

How can short sightedness be corrected?

Answer 10

With glasses or contact lenses using concave lenses.

Question 11

What way does a concave lens curve and where is its thinnest point?

Answer 11

A concave lens curves inwards, so its thinner in the centre than at the edge.

Question 12

How does a concave lens help correct vision for short sighted people?

Answer 12

The lens refracts light so that light rays diverge (more apart) before they enter the eye.

The reduction in convergence allows the image to be brought into focus on the retina.

Question 13

What are cataracts?

Answer 13

A cloudy patch on the lens which stops light from entering the eye normally.

Question 14

Why do cataracts often occur in older people?

Answer 14

Because tissues in the eye degrade over time.

Question 15

How is vision effected for a person with cataracts?

Answer 15

They are likely to have blurred vision.

Colours may look less vivid.

May have difficulty seeing in bright light.

Question 16

How are cataracts treated?

Answer 16

By replacing a faulty lens with an artificial one made of clear plastic.

Question 17

What are the risks associated with cataract treatments?

Answer 17

There is a risk of complication ( as with all surgical procedures), including possible damage to the retina, which could lead to loss of sight.

Question 18

Give one way cataracts can be corrected.(1 mark)

Answer 18

By replacing the faulty/cloudy lens with an artificial one made of clear plastic.

Question 19

Explain the cause of short sightedness.(3 marks)

Answer 19

The lens is the wrong shape/refracts the light too much, or the eyeball,is too long (1 mark)

So light rays do not converge on the retina (1 mark) and images of distant objects are brought into focus in front of the retina (1 mark)