The document discusses the structure and function of the human eye. It describes the external structures like the sclera, iris, cornea, and conjunctiva. Internally, it outlines the lens, retina, and optic nerve. The lens focuses light onto the retina, where light is converted to electrical signals sent by the optic nerve to the brain for processing. The iris controls the size of the pupil to regulate the amount of light entering the eye. Together, these structures work to capture light and transmit visual information to the brain.

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

2. 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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3. The External Structure of the Eye
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4. Structure of the Eye
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5. 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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6. 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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7. 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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8. 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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9. 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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10. Lens: Focusing Light
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11. Lens: Sight Defects
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12. 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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13. 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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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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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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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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17. Colour Blindness Test
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18. Colour Blindness Test
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19. Colour Blindness Test
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20. Colour Blindness Test
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21. Colour Blindness Test
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