Homeostasis - The Eye

Question 1

What is the eye?

Answer 1

a sensory organ

Question 2

Name all the parts of the eye

Answer 2

• cornea
• sclera
• retina
• iris
• pupil
• ciliary muscle
• suspensary ligaments
• lens
• optic nerve

Question 3

What is the function of the cornea?

Answer 3

The outer layer of the eye that refracts light

Question 4

What is the function of the sclera?

Answer 4

The tough, supporting wall of the eye

Question 5

What is the function of the iris?

Answer 5

Controls how much light enters the eye (contains muscles that control the diameter of the pupil)

Question 6

What is the function of the lens?

Answer 6

Focuses the light onto the retina

Question 7

What is the function of the optic nerve?

Answer 7

Carries impulses from receptors on the retina to the brain

Question 8

What is the function of the retina?

Answer 8

Contains light receptor cells that are sensitive to light intensity and colour of light

Question 9

What is the function of the ciliary muscles?

Answer 9

Controls the shape of the lens

Question 10

What is the function of the suspensary ligaments?

Answer 10

Controls the shape of the lens

Question 11

How does the eye react when walking into a bright room?

Answer 11

The circular muscles contract
The radial muscles relax

Question 12

How does the eye react when walking into a room with dim light?

Answer 12

The circular muscles relax
The radial muscles contract

Question 13

What does it mean to be long-sighted?

Answer 13

You can’t see objects clearly up close, but you can see objects in the distance

Question 14

What does it mean to be short-sighted?

Answer 14

You can’t see objects clearly in the distance, but you can see objects up close

Question 15

Why are people long-sighted?

Answer 15

• the lens is the wrong shape
• not enough light is refracted
• the eye-ball is too short
• the images of near objects are brought into focus behind the retina

Question 16

Why are people short-sighted?

Answer 16

• the lens is the wrong shape
• there’s too much light being refracted
• the eye-ball is too long
• images of distant objects are brought into focus in front of the retina

Question 17

What is the medical term for long-sightedness?

Answer 17

hyperopia

Question 18

What is the medical term for short-sightedness?

Answer 18

myopia

Question 19

How do contact lenses (both soft and hard) treat vision defects and what are the advantages and disadvantages of it?

Answer 19

How does it work:
- the lenses sit on the surface of the eye
- are shaped to compensate the fault in focusing

Advantages:
- they are light-weight and almost invisible
- more convenient when playing sport

Disadvantages:
- soft lenses are more comfortable, but they have a higher risk of infection than hard lenses

Question 20

Describe how laser-eye surgery can treat vision defects and what are the advantages and disadvantages of it?

Answer 20

How does it work?
- can be used to vapour tissue, changing the shape of the cornea. (changing how strongly it refracts light into the eye)
- improves short sight - slims it down to make it less powerful
- improves long sight - changing the shape so it’s more powerful

Advantages:
- surgeons can precisely control how much tissue the laser takes off, completely correcting vision

Disadvantages:
- eye can get infected
- reaction in the eye that makes your vision worse than it was before

Question 21

Describe how replacement lens surgery treats vision defects and what are the advantages and disadvantages of it?

Answer 21

How does it work?
- Natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place

Advantages:
- is more effective when treating long-sightedness (rather than altering the shape of the cornea with laser-eye surgery)

Disadvantages:
- involves work inside the eye: replacing a lens carries higher risks than laser-eye surgery
- possible damage to the retina –> lead to loss of sight
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