Chapter 1 (1.2 : Eye)

Question 1

What is the function of eye lens?

Answer 1

-Bends and focuses light to form an image on the retina
-The thickness of the lens can be altered to focus near and distant object

Question 2

What is the function of iris?

Answer 2

Controls the size of the pupil and hence the amount of light entering the eye

Question 3

What is the function of vitreous humour?

Answer 3

-Helps refract light and focus the image onto the retina
-Helps to maintain the shape of the eye and the pressure in the eye

Question 4

What is the function of conjunctiva?

Answer 4

Protects the cornea

Question 5

What is the function of cornea?

Answer 5

-Helps to focus light onto the retina by bending light rays passing through it
-Allow light to enter the eye
-Prevent internal reflection of light in the eye

Question 6

What is the function of pupil?

Answer 6

Allow light to pass into the eye

Question 7

What is the function of suspensory ligament?

Answer 7

Hold the lens in place and connect it to the ciliary body

Question 8

What is the function of ciliary muscles?

Answer 8

-Contracts and relaxes to change the thickness of the lens
-Changes the focal length of the lens

Question 9

What is the function of sclera?

Answer 9

-Protects and shapes the eye

Question 10

What is the function of optic nerve?

Answer 10

Sends nerve impulses from the retina to the brain to be interpreted

Question 11

What is the function of fovea(yellow spot)?

Answer 11

Detects the images of the objects formed and give the clearest vision

Question 12

What is the function of retina?

Answer 12

-Detects light stimuli and sends information in the form of nerve impulses to the brain
-Has many receptors that are sensitive to light
(Photoreceptors : rods and cones)
-Rods: sensitive to different light intensities including dim light but not sensitive to coloured lights
-Cones: sensitive to coloured lights in bright conditions only, there are three types of cone cells which are sensitive to red, blue aand green lights

Question 13

What’s the function of photoreceptors (cones and rods)?

Answer 13

Cones : Sensitive to coloured light in bright conditions (red, blue, green)
Rods : Sensitive to different light intensities including dim light but not sensitive to colour light

Question 14

What are the characteristics of a blind spot

Answer 14

-This point of retina is not sensitive to light
-Images falling on this spot cannot be detected because there are no receptors cells on this spot
-Spot where optic nerve leaves the eye ball

Question 15

Which part of the eye is thin, transparent and self-repairing membrane?

Answer 15

Conjunctiva

Question 16

Which part of the eye is curved, transparent layer at the front of the eyes is a continuation of the sclera?

Answer 16

Cornea

Question 17

Which part of the eye is the outer layer of the eyeball, white, tough and opaque?

Answer 17

Sclera

Question 18

What’s the function of choroid

Answer 18

The capillaries supply nutrients and oxygen to the eye

Question 19

What is the middle layer of the eyeball called?

Answer 19

Choroid

Question 20

State the order of sight mechanism of humans

Answer 20

Light rays -> Cornea -> Eye lens -> Retina -> Optic nerve -> Brain

Question 21

When does an optical illusion occur?

Answer 21

An optical illusion occurs when the brain does not interpret the nerve impulses accurately

Question 22

What examples of devices are used to overcome the limitations of sight?

Answer 22

-Microscope
-Magnifying glasses
-Telescope
-Binoculars
-X-rays
-Ultrasound scanning device

Question 23

What are the common defects of vision?

Answer 23

-Short-sightedness (myopia)
-Long-sightedness (hypermetropia)
-Astigmatism
-Colour blindness
-Presbyopia

Question 24

What are the similarities between short-sightedness (myopia) and long-sightedness (hypermetropia)?

Answer 24

Caused by the condition of the lens and the shape of the eyeball

Question 25

What are the characteristics of short-sightedness?

Answer 25

Condition of person -Sees nearly objects clearly but can’t focus on distant objects Focus -Light from a distant object is focused in front of the retina Causes -Eye lens is too thick -Eye ball is too long

Question 26

What are the characteristics of long-sightedness?

Answer 26

Condition of person -Sees nearly objects clearly but can’t focus on distant objects Focus -Light from a near object is focused behind of the retina Causes -Eye lens is too thin -Eye ball is too short

Question 27

What correction is made in order to see clearly with short-sightedness?

Answer 27

-Use glasses with **concave lenses** Concave lenses -Diverges the light rays before they enter the eye -The diverging rays are focused onto the retina by the lens to form a sharp image

Question 28

What correction is made in order to see clearly with long-sightedness?

Answer 28

-Use glasses with **convex lenses** Convex lenses -Converges the light rays -The converging light rays are focused onto the retina by the lens to form a sharp image

Question 29

What causes astigmatism?

Answer 29

-Astigmatism is caused by irregular surface of the cornea, or a lens that is not evenly curved -The vertical and horizontal rays from the image cannot be focused at the same time

Question 30

What does the person with astigmatism see? Explain your answer

Answer 30

A person with astigmatism sees some parts of an object more clearly than others because the image formed on the retina is distorted and not very clear.

Question 31

What causes colour blindness?

Answer 31

Colour blindness is caused by a shortage of cone cells (colour receptor cells) on the retina

Question 32

What causes presbyopia?

Answer 32

Presbyopia is caused when a person gets older, the **eye lens becomes harder** and **less elastic**.The muscles in the **ciliary muscles loses their ability to contract and relax**. As a result, both near and far objects cannot be focused on the retina.