1. The Structure and Function of the Eye
SCIENCE CLASS 8
UZMA AMER

2. Structure and Function of the Eye
Windows to the World
Eyes are photosensitive organs designed to detect light and pass on the information as electrical signal to the brain.
Vision such as ours and animals are know as ‘camera’ like vision.
Camera like vision has evolved at least seven separate times through out natures history.
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Structure and Function of the Eye

3. The External Structure of the Eye
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Structure and Function of the Eye

4. Structure and Function of the Eye
Structure of the Eye
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Structure and Function of the Eye

5. Structure and Function of the Eye
Sclera
The sclera, commonly known as "the white of the eye," is the tough, opaque tissue that serves as the eye's protective outer coat.
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Structure and Function of the Eye

6. Structure and Function of the Eye
The Iris
The coloured part of the eye is called the iris.  It controls light levels inside the eye similar to the aperture on a camera. 
The round opening in the centre of the iris is called the pupil. 
The iris is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size. 
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Structure and Function of the Eye

7. Structure and Function of the Eye
The Cornea
The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye's focusing power. Like the crystal on a watch, it gives us a clear window to look through
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Structure and Function of the Eye

8. Structure and Function of the Eye
Conjunctiva
The conjunctiva is the thin, transparent tissue that covers the outer surface of the eye. 
It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids. 
It is nourished by tiny blood vessels that are nearly invisible to the naked eye.
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Structure and Function of the Eye

9. Structure and Function of the Eye
Lens
The purpose of the lens is to focus light onto the back of the eye. 
The nucleus, the innermost part of the lens is surrounded by softer material called the cortex. 
The lens is encased in a capsular-like bag and suspended within the eye by tiny guy wires called zonules.
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Structure and Function of the Eye

10. Structure and Function of the Eye
Lens: Focusing Light
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Structure and Function of the Eye

11. Structure and Function of the Eye
Lens: Sight Defects
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Structure and Function of the Eye

12. Structure and Function of the Eye
Retina
The retina is a very thin layer of tissue that lines the inner part of the eye.
It is responsible for capturing the light rays that enter the eye.  Much like the film's role in photography.  
These light impulses are then sent to the brain for processing, via the optic nerve.
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Structure and Function of the Eye

13. Structure and Function of the Eye
Optic Nerve
The optic nerve transmits electrical impulses from the retina to the brain.
It connects to the back of the eye near the macula.
The visible portion of the optic nerve is called the optic disc.
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Structure and Function of the Eye

14. Optic Nerve: Blind Spot
Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot.
Take a piece of paper and draw a dot and 10 cm to the left an x.
Close your right eye and hold the paper at arms length.
Look at the dot and move the paper towards you.
What happens to the X?
It disappears into the blind spot!
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Structure and Function of the Eye

15. Eyes and Animation (Off Syllabus)
There is a .4 second delay in response from the time the image falls on the retina. The sensation may persist for up to 2 minutes.
This after image effect is exploited by film, TV and computer monitors which display a rapid succession of still images, which are refreshed before the perceptual image has decayed.
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Structure and Function of the Eye

16. Eye Disorders (Off Syllabus)
About one in ten men and one in a hundred women experience some form of divergent colour perception.
The most common is confusion between red and green. This can cause some problems in colour matching.
The genes for colour blindness located on the X chromosome.
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Structure and Function of the Eye

17. Structure and Function of the Eye
Colour Blindness Test
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Structure and Function of the Eye

18. Structure and Function of the Eye
Colour Blindness Test
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Structure and Function of the Eye

19. Structure and Function of the Eye
Colour Blindness Test
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Structure and Function of the Eye

20. Structure and Function of the Eye
Colour Blindness Test
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Structure and Function of the Eye

21. Structure and Function of the Eye
Colour Blindness Test
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Structure and Function of the Eye