## Step5

The lens

Study the text and do the assignment below:

The lens makes sure the light is refracted (refracted means 'to bend light'). Straight rays of light falling onto the eye will pass through the focal point. The ciliary body can change the shape of the lens to change the focus. On the retina a sharp image will be shown. Inside the retina light sensitive cells will create an impulse to be sent to the brain through the optic nerve. Your eye and you! A lesson in lens accommodation, by Maxwell Yeager. When the lens in your eye isn't the right shape, or has become rigid with age, the focal point might not be exactly on your retina and you might need glasses. There are two types of lenses for glasses, concave and convex. In the picture below you see the difference. Near-sightedness is corrected with a concave lens, far-sightedness is corrected with a convex lens.

The lens

near-sighted - concave - convex - brain - focal point - far-sighted - retina

Light rays enter the eye through the pupil and pass through the lens. In the back of your eye the light falls onto the ..1.. . The light is refracted in such a way, a clear image appears on the retina, but upside down! Your ..2.. turn this image around. Sometimes the lens does not work properly. You might be ..3.. or far-sighted and need glasses. In near-sighted people the lens bends the light too much. The ..4.. will not reach the retina. Somebody who is near-sighted needs glasses with ..5.. lenses. In ..6.. people it is just the other way around. The lens does not bend the light enough. The focal point will be behind the retina. Somebody who is far-sighted, needs glasses with ..7.. lenses.

1 = ...

2 = ...

3 = ...

4 = ...

5 = ...

6 = ...

7 = ...