5. Homeostasis and Response (the eye)

Question 1

What is an eye?

Answer 1

A sense organ containing receptors sensitive to light intensity and colour

Question 2

What are the 7 structures of the eye?

Answer 2

• Retina
• Optic nerve
• Sclera
• Cornea
• Iris
• Ciliary muscles and Suspensory ligaments

Question 3

What is the retina?

Answer 3

A layer of light sensitive cells found at the back of the eye

Question 4

What is the function of the retina?

Answer 4

• When light hits it, the cells are stimulated
• impulses are sent to the brain, which interprets the information to create an image

Question 5

What is the optic nerve?

Answer 5

A nerve that leaves the eye and leads to the brain

Question 6

What is the function of the optic nerve?

Answer 6

It carries the impulses from the retina to the brain to create an image

Question 7

What is the sclera?

Answer 7

The white outer layer which supports the structures inside the eye

Question 8

How is the sclera adapted for its function?

Answer 8

It is strong/tough to prevent damage to the eye

Question 9

What is the cornea?

Answer 9

The curved, transparent layer at the front of the eye

Question 10

What is the function of the cornea?

Answer 10

It allows light through and the curved surface bends and focuses light on the retina

Question 11

What is the iris?

Answer 11

Muscles that surround the pupil

Question 12

What muscles is the iris made up of?

Answer 12

• Circular muscles and Radial muscles

Question 13

What is the function of the iris?

Answer 13

to contract or relax to alter the size of the pupil

Question 14

What does the iris do when there is bright light?

Answer 14

in bright light, the circular muscles contract and radial muscles relax to make the pupil smaller

Question 15

What does the iris do when there is dim light?

Answer 15

in dim light, the circular muscles relax and the radial muscles contract, to make the pupil larger

Question 16

Why is the pupil made smaller in bright light?

Answer 16

To avoid damage to the retina

Question 17

Why is the pupil made bigger in dim light?

Answer 17

so more light can enter to create a better image

Question 18

What is the process of accommodation?

Answer 18

The process of changing the shape of the lens to focus on near or distant objects

Question 19

What do the ciliary muscles and suspensory ligaments do?

Answer 19

they hold the lens in place and control its shape

Question 20

How does focussing on near objects work?

Answer 20

• The ciliary muscles contract
• The suspensory ligaments loosen
• The lens is then thicker and more curved
• so light is refracted more

Question 21

If you have a thicker and
more curved lens, what happen?

Answer 21

light is refracted more

Question 22

How does focussing on distant objects work?

Answer 22

• The ciliary muscles relax
• The suspensory ligaments tighten
• Then lens then becomes thinner
• so light is refracted less

Question 23

If you have a thinner lens, what happens?

Answer 23

light is refracted less

Question 24

When do eye defects occur?

Answer 24

When light cannot focus on the retina

Question 25

What is short-sightedness called?

Answer 25

myopia

Question 26

What is myopia?

Answer 26

when the lens is too curved, so distant objects appear blurry

Question 27

What is long-sightedness called?

Answer 27

hyperopia

Question 28

What is hyperopia?

Answer 28

when the lens is too flat, so it cannot refract light enough

Question 29

What are the different treatment methods for eye defects?

Answer 29

1. Spectacle lenses (glasses)
2. Contacts
3. Laser eye surgery
4. Replacement lens

Question 30

What are spectacle lenses and how are they used to treat myopia and hyperopia?

Answer 30

• glasses with concave lenses to spread out the light rays to treat myopia
• glasses with convex lenses to bring the light rays together to treat hyperopia

Question 31

How do contact lenses work?

Answer 31

They work in the same way as glasses, but allow activities such as sport to be carried out

Question 32

How does laser eye surgery work to treat myopia?

Answer 32

lasers can be used to reduce the thickness of the cornea, so it refracts light less

Question 33

How does laser eye surgery work to treat hyperopia?

Answer 33

lasers can be used to change the curvature of the cornea, so it refracts light more strongly

Question 34

How can hyperopia be treated with a replacement lens?

Answer 34

The lens can be replaced with an artificial one made of clear plastic, or adding plastic on top of the natural lens

Question 35

What are the risks of a replacement lens?

Answer 35

• damage to retina
• cataracts developing

Question 36

What are the two types of contact lenses?

Answer 36

• Hard - rigid material, lasts a long time, must be kept sterile
• Soft - flexible material, lasts for a shorter time, more comfortable