1. Gr.12 Life Sciences The eye

2. The Human Eye

3. Others see the opposite.
Most people see the red,
Closer than the blue.
Others see the opposite.
How about you?

4. The Human Eye
Your eyes are about to get a workout. Have you stretched your eye muscles yet?
No? Then do that now!

5. Are you seeing spots?

7. Look at the cross for 10 seconds. What do you see?

8. Are these lines bent….?

9. …or straight?

10. What shapes do you see?

13. What is wrong with this sentence?
Reading
Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

14. The Eye The Structure and function
Cornea: Responsible for the refraction (bending) of light rays from the object, to create the
image on the
retina
Pupil: A circular
opening in the iris which allows light into the eye
The Structure and function
Optic nerve:
Carries nerve impulses from the retina to the brain
Retina: Contains
the light-sensitive
receptor cells, i.e.
the rods and cones
Iris: The coloured
part of the eye
Sclera: The tough
white outer coat,
which protects the
eye against damage
Lens: Changes
shape for near
and distant
(far) vision
Choroid: A dark coloured layer
which:
• Reduces reflection
• Is rich in blood vessels which
supply the cells of the eye with
nutrients and oxygen
Vitreous humour:
A jelly-like substance which gives shape to the
eye

15. The Eye Functioning of the eye
The eye performs the following functions:
Binocular vision
Formation of the image
Accommodation
Pupillary reflex

16. Binocular Vision
Refers to the ability to focus on an object with both eyes, creating a single image
During binocular vision the three pairs of muscles on the outside of each eye enable the eye to see three dimensionally.
The ability to perceive depth is known as stereoscopy or stereoscopic vision
Depth of perception enables us to walk down/up stairs.

17. Accommodation
Refers to the ability of the eye to change the shape (convexity) of the lens to ensure a clear image is formed on the retina whether the image is near or distant to bend the light more to focus it
Fat lens needed

18. Pupillary Mechanism Controlling light levels
Your eye are very sensitive and can be damaged by harsh light.
Your iris controls light allowed into the eye by changing the size of the pupil
In bright light
The circular muscles of the iris contract
The radial muscles relax
The pupil constricts
The amount of light entering the eye is reduced
Sclera
Pupil
Constricts
(becomes
Smaller)
Radial
muscles of
Iris relax
Circular muscles of iris contract

19. The radial muscles of the iris contracts The circular muscles relax
Pupillary Mechanism
In dim light
The radial muscles of the iris contracts
The circular muscles relax
The pupil dilates
The amount of light entering the eye is increased.
Sclera
Circular
muscles
of iris relax
Pupil
widens
Radial
muscles of
of iris contract

20. Hypermetropia (long sightedness)
Nature and treatment of visual defects
Hypermetropia (long sightedness)
Causes :
Eyeball being too rounded
Inability of the lens to become more convex common in the elderly
Treatment
Wear classes with convex lens

21. Myopia (short sightedness)
Nature and treatment of visual defects
Myopia (short sightedness)
Causes :
Eyeball being too long
Inability of the lens of the eye to become less convex.
Treatment
Wear glasses with a concave lens.

22. Astigmatism Nature and treatment of visual defects
The front surface of the cornea is curved more in one direction than in the other.
Symptoms:
Distortion or blurring of images at all distances
Headache and fatigue squinting and eye discomfort and irritation
Treatment
Prescription glasses are required if the degree of astigmatism is great enough to cause eye strain and head ache, or distortion of vision.

23. Cataracts Nature and treatment of visual defects Refers to:
The cloudy, opaque part of the lens not clear understanding of its causes.
Treatment:
Surgical removal of the lens replacing the lens with a synthetic lens.

24. Questions
1. Various possible options are provided as answers to the following questions. Choose
the correct answer and write only the letter (A – D) next to the question number.
Refer for to the diagram of the human eye below for 1.1 to 1.3 :
1.1 The parts that control the amount of light rays that enter the eye are…..
A 1 and 2
B 1 and 3
C 2 and 3
D 3 and 4

25. Questions
1.2 The greatest convergence takes place when light rays pass through the part
numbered…..
A 4
B 5
C 6
D 11
13 The function of part numbered 9 is to:
1. reflect light
2. change the shape of the eyeball
3. refract light rays
4. prevent reflection
5. supply the retina with nutrients and oxygen
6. absorb excess light
Choose the correct options for the function of part no.9
A 1, 2, 3
B 4, 5, 6
C 2, 4, 6
D 1, 3, 5

26. Questions 1.4 The following are part of the human eye:
1 cornea 2 lens 3 retina 4 iris 5 choroid
Which parts are respectively concerned with/in:
• Adjusting the focus?
• Preventing internal reflection?
• Recording changes in light intensity?
A 2, 4 and 3
B 3, 4 and 1
C 2, 5 and 4
D 4, 1 and 5

27. Answers
1.1. C √ √
1.2. C √ √
1.3. B √ √
1.4. C √ √

28. Questions
1.5 The diagram alongside that represents a section through part of the human eye.
Supply labels for the parts numbered 1, 3 and 5. (3)
Supply the number and name the part that controls the amount of light that
enters the eye. (2)
1.5.3 Mention the changes that the part names in Question will undergo when
exposed to bright light. (4)
List one function for each of parts 4 and 7.
(2)

29. 1.5.5 Supply the number and the name of the part that is responsible for the accommodation of the eye. (2)
Explain the changes that will take place when the part named in Question views an object closer that 6m.

30. 1.5.1. 1 = cornea√ 3= pupil √ 5 = suspensory ligaments √
Number 2 , the iris √
The radial muscles of the iris relax the circular muscles contract
this will cause the pupil to constrict √ allowing less light to enter into the eye √
Part 4 = the lens focusses the light rays onto the retina at the back of the
eye √ .
Part 7 = the vitreous body / vitreous humour is part of the refracting medium of
the eye and helps to maintain the shape of the eyeball. √
1.5.5 Number 6 = the ciliary muscles in the ciliary body √ √
1.5.6.
• The ciliary muscles contract √
• Releasing the tension on the suspensory ligaments so they become
relaxed √
• The tension on the elastic lens becomes less √
• The lens becomes rounder/more convex √
• This increases the refraction of light through the lens so that the image
focusses on the retina √ (18)

31. Practical work