The Eye

Question 1

What is the eye?

Answer 1

A sense organ.

Question 2

What is the sclera?

Answer 2

The tough, supporting wall of the eye.

Question 3

What is the cornea?

Answer 3

The transparent outer layer found at the front of the ey. It refracts (bends) light into the eye.

Question 4

What does the iris do?

Answer 4

Contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye.

Question 5

What does the lens do?

Answer 5

Focuses the light onto the retina (which contains cells sensitive to light intensity and colour).

Question 6

What is the shape of the lens controlled by?

Answer 6

The ciliary muscles and suspensory ligaments.

Question 7

What does the optic nerve do?

Answer 7

Carries impulses from the receptors on the retina to the brain.

Question 8

What can damage the retina? How can it be protected?

Answer 8

Very bright light - so you have a reflex to protect it.

1. When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. This reduced the amount of light that can enter the eye.
2. The opposite process happens in dim light. This time, the radial muscles contract and the circular muscles relax, which makes the pupil wider.

Question 9

How does the eye focus light on the retina?

Answer 9

By changing the shape of the lens - known as accommodation.

Question 10

Explain how the eye focuses on an object that is close to it.

Answer 10

1. The ciliary muscles contract (pull tight), which allows the suspensory ligaments to relax.
2. The lens become fat (more curved).
3. This increases the amount by which it refracts light.
   [Ciliary muscles tighten, suspensory ligaments relax]

Question 11

Explain how the eye focuses on an object that is far from it.

Answer 11

1. The ciliary muscles relax, which allows the suspensory ligaments to pull tight.
2. This makes the lens go thin (less curved)
3. So it refracts light by a smaller amount.

Question 12

Why do older people often have to use reading glasses?

Answer 12

As you get older, your eye’s lens loses flexibility, so it can’t easily spring back to a round shape. This means light can’t be focused well for near viewing, so older people often have to use reading glasses.