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Sight 11.2.

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Presentation on theme: "Sight 11.2."— Presentation transcript:

1 Sight 11.2

2 The structure of our eye
eyeball eye muscles orbit (眼窩) eye muscles skull

3 How do we see?

4 How is an image formed in the eye?
3 The light-sensitive cells on the retina are stimulated by light.

5 How is an image formed in the eye?
The process of how we see: light from an object cornea lens bends the light

6 How is an image formed in the eye?
The process of how we see: lens retina bends the light which is then focused onto

7 light-sensitive cells (receptors)
How is an image formed in the eye? The process of how we see: retina light-sensitive cells (receptors) contains

8 light-sensitive cells (receptors)
How is an image formed in the eye? The process of how we see: light-sensitive cells (receptors) brain stimulated by the light and send messages to

9 upright image of the object
How is an image formed in the eye? The process of how we see: brain upright image of the object interprets the messages as

10 How is an image formed in the eye?
3 They send messages to the brain along the optic nerve. brain

11 How is an image formed in the eye?
4 The brain interprets the messages as an upright image.

12 Seeing objects at different distances
focusing on the words near objects

13 Seeing objects at different distances
focusing on the bird distant object

14 Seeing objects at different distances
How can we see objects at different distances?

15 11.3 Focusing with lenses of different thickness screen
Experiment video Focusing with lenses of different thickness screen thin convex lens 1 light source

16 Seeing objects at different distances
our lens is elastic

17 Seeing objects at different distances
thickness can be changed

18 Seeing distant objects

19 Seeing distant objects
light from a point on a distant object lens becomes thinner

20 Seeing near objects

21 Seeing near objects light from a point on a near object lens becomes thicker

22 Seeing objects at different distances
When we look at distant objects, the lens becomes thinner.

23 Seeing objects at different distances
When we look at near objects, the lens becomes thicker.

24 Seeing colours cone cell (視錐細胞) rod cell (視桿細胞)

25 Seeing colours cone cell (視錐細胞) rod cell (視桿細胞)
responsible for black and white vision

26 Seeing colours cone cell (視錐細胞) rod cell (視桿細胞)
important for vision in dim light

27 Seeing colours cone cell (視錐細胞) rod cell (視桿細胞)
works best in bright light

28 Seeing colours cone cell (視錐細胞) rod cell (視桿細胞)
responsible for colour vision

29 Seeing colours red cone cell green cone cell blue cone cell

30 Seeing colours red cone cell green cone cell blue cone cell red light
sensitive to red cone cell green cone cell blue cone cell red light green light blue light

31

32

33

34 Seeing colours There are two types of light-sensitive cells on the retina: rod cells are responsible for black and white vision; cone cells are responsible for colour vision.

35 35 2 2a Light is focused onto the retina by the sclera. T F

36 36 2 b When seeing a distant object, the lens becomes thinner. T F

37 37 2 c The rod cells on the retina allow us to see when there is no light in our surroundings. T F

38 2 Well done! 3 Cone cell Rod cell _______ types (sensitive to _______,
38 2 Well done! 3 Cone cell Rod cell _______ types (sensitive to _______, _______ and _______ light) _______ type only Work well in _______ light Work well even in _______ light Responsible for _______ vision Responsible for _______ ___________ vision Three red One green blue bright dim colour black and white

39 The limitations of our eyes
Tap water looks clean. Let me drink it directly. I’m very thirsty.

40 The limitations of our eyes
Don’t do that! There may be harmful bacteria in tap water.

41 The limitations of our eyes
They are too small to be seen.

42 The limitations of our eyes
Our eyes cannot see clearly when the object is too small, too near or too far away.

43 Astronomical telescope
11.3 Instruments Hand lens Microscope Binoculars Astronomical telescope Flying birds in the sky Small insects Onion cells Jupiter Objects

44 The limitations of our eyes
Using suitable instruments can help us see objects that are too small or too far away.

45 Blind spot Is there any other limitation of our eyes?

46 11.4 Where has the rabbit gone? 1 Hold your book. 30 cm

47 11.4 2 Cover your left eye and look at the hunter on your book with your right eye.

48 11.4 3 Move the book towards you slowly.

49 11.4 3 What happens to the rabbit? The rabbit disappears when the book is held at a certain distance.

50 Blind spot retina no light-sensitive cell blind spot optic nerve

51 Blind spot image formed on the blind spot no message will be sent

52 Blind spot We cannot see the images formed on the blind spot.

53 Common eye defects (眼睛毛病):
short sight (近視) long sight (遠視) cataract (白內障) astigmatism (散光) glaucoma (青光眼) colour blindness (色盲)

54 but not distant objects
Short sight and long sight People with short sight can see: near objects clearly; but not distant objects

55 distant objects clearly;
Short sight and long sight People with long sight can see: distant objects clearly; but not near objects

56 Short sight and long sight
What are the causes of short sight and long sight? How can they be corrected?

57 11.4 Short sight, long sight and their corrections 1
Experiment video Short sight, long sight and their corrections 1 fluorescent solution round-bottomed flask

58 58 11.4 5a concave lens (凹透鏡) convex lens (凸透鏡)

59 Short sight Short sight may be caused by: OR OR BOTH lens being too thick eyeball being too long

60 Short sight cannot see distant objects clearly

61 Short sight image formed in front of the retina light from a distant object

62 Short sight Correction sharp image formed on the retina concave lens

63 eyeball being too short
Long sight Long sight may be caused by: OR OR BOTH lens being too thin eyeball being too short

64 Long sight cannot see near objects clearly

65 Long sight image formed behind the retina light from a near object

66 Long sight sharp image formed on the retina Correction convex lens

67 Cataract lens becomes cloudy

68 Cataract cloudy lens blocks some of the light
blurred vision, even blindness

69 Cataract Smoking Eye Diabetes injuries Risk factors Prolonged exposure
to sunlight Ageing

70 Cataract can be cured by: replacing it with an artificial lens

71 Astigmatism cornea or lens being irregularly shaped
light cannot focus on the retina as a sharp image blurred vision

72

73 Astigmatism Causes: inherited
incorrect posture or an increased use of the eyes for close work

74 Astigmatism Correction:
wear lenses that are curved to suitable degrees at different points

75 Glaucoma caused by an increased fluid pressure in the eye
the optic nerve will be damaged gradually loss of peripheral vision

76 loss of peripheral vision
Glaucoma loss of peripheral vision

77 Glaucoma In serious cases loss of central vision and blindness

78 Glaucoma no cure if detected early and treated properly, further damage to vision may be prevented

79 Glaucoma Treatments: eye drops drugs surgery

80 Colour blindness People with colour blindness cannot distinguish some or all colours.

81 Colour blindness cone cells not working properly

82 Colour blindness The most common form is red-green colour blindness.

83 red-green colour blindness
The image seen by people with: red-green colour blindness normal sight

84 Colour blindness inherited; cannot be corrected
more commonly found in males

85 Colour blindness What do you see in the diagrams? 29 2 6

86 No number/ drawing could be seen
Colour blindness What do you see in the diagrams? No number/ drawing could be seen drawing of a camel

87

88 Answer: Everyone should be able to see a circle, star, and square in the demonstration plate.

89

90

91 Eye defects Short sight, long sight, cataract, astigmatism, glaucoma and colour blindness are some common eye defects.

92 Eye care 1 Read under sufficient but not strong light.
Keep a distance of 30 cm

93 Eye care 2 Keep a distance of 40 to 60 cm

94 Eye care 3 After reading a book or using a computer for 30 minutes,
Take a 5 to 10-minute break

95 Eye care 4 Wear sunglasses under strong sunlight.

96 Eye care 5 Have regular eye checks.

97 Eye care 6 Do not rub your eyes to avoid infection.

98 3 1 Eye defect Problem Cause Correction Short sight Cannot see
98 3 1 Eye defect Problem Cause Correction Short sight Cannot see _________ objects clearly Lens too and/or eyeball too Wear lenses distant thick concave long

99 3 1 Eye defect Problem Cause Correction Long sight Cannot see ________
99 3 1 Eye defect Problem Cause Correction Long sight Cannot see ________ objects clearly Lens too ________ and/or eyeball too ________ Wear ________ lenses near thin convex short

100 3 1 Eye defect Problem Cause Correction Cataract ________ vision
100 3 1 Eye defect Problem Cause Correction Cataract ________ vision Blurred Lens becomes ________ Replace the ________ with an artificial one lens cloudy

101 3 1 Eye defect Problem Cause Correction Astigmatism ________ vision
101 3 1 Eye defect Problem Cause Correction Astigmatism ________ vision Blurred ________ or _______ irregularly shaped Cornea Wear lenses that are curved to suitable degrees at different points lens

102 3 1 Eye defect Problem Cause Correction Glaucoma Vision loss
102 3 1 Eye defect Problem Cause Correction Glaucoma Vision loss Increased fluid _________ in the eye damages the optic nerve Early detection and treatment can prevent or ________ further damage to vision pressure delay

103 3 1 Eye defect Problem Cause Correction Colour blindness
103 3 1 Eye defect Problem Cause Correction Colour blindness Cannot distinguish ________ One or more types of the _________ not working properly Cannot be corrected colours cone cells

104 104 3 2a We can see distant objects clearly with the help of a hand lens. T F

105 105 3 b Light from an object can be focused on the blind spot. T F

106 106 3 Very good! c Colour blindness is caused by defects in the rod cells on the retina. T F

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