The Human Eye Day 18
Transcript of The Human Eye Day 18
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THE HUMAN EYE
BYSTEFFY AGNES .V.B
NATURAL SCIENCE
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HUMAN EYE
A human eyeball is like asimple camera!Sclera: outer walls, hard, like alight-tight box.
Cornea and crystalline lens(eyelens): the two lens system.
Retina:at the back of eyeball,like the film.
Iris: like diaphragms or stop ina camera.
Pupil: camera aperture.Eyelid: lens cover.
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THE HUMAN EYE
Refractive index of lens
different for each
wavelength (colour)
Cool colours (blues)
appear closer; warm
colours (reds) further
away.
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Most people see the red,
Closer than the blue.Others see the opposite.
How about you?
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THE HUMAN EYE
Your eyes are about to get a workout.
Have you stretched your eye musclesyet?
No? Then do that now!
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ARE YOU SEEING SPOTS?
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LOOK AT THE CROSS FOR 10 SECONDS.
WHAT DO YOU SEE?
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WHAT SHAPES DO YOU SEE?
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DO YOU SEE THE RABBIT OR THE
DUCK?
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READ THIS OUT LOUD.
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ARE YOU SURE? READ AGAIN.
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THE HUMAN EYE
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STRUCTURE & FUNCTION
IRIS
coloured part of eye
controls light
entering
PUPIL
black hole in iris
where light enters
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STRUCTURE & FUNCTION
SCLERAwhites of the eyesupports eyeballprovides
attachment formuscles
LENS
converging lensallows us to seeobjects near and far
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STRUCTURE & FUNCTION
CORNEAtransparent bulgeover pupil
focuses light(refracts) onto retina
RETINAinternal membranecontain light-receptive cells (rods
& cones)converts light toelectrical signal
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BLIND SPOT
On retina where optic
nerve leads back into
the brain
No rod or cone cellsOther eye compensates
for this area
Try this test to prove
you have a blind spot
CLOSE LEFT EYE AND
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CLOSE LEFT EYE AND
APPROACH SCREEN WHILE
STARING AT THE LETTERSWATCH THE DOT!
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STRUCTURE & FUNCTION
OPTIC NERVE
Transmits electrical
impulses from retina to
the brain.Creates blind spot
Brain takes inverted
image and flips it so we
can see.
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STRUCTURE & FUNCTION
RODS120 million cells
detect brightness
(black & white)
for night visionCONES6 million cells
detect colour (RGB)
GANGLION CELLSDetect movement and
patterns
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NORMAL EYE FOCUS
Blind spot
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FOCUSING PROBLEMS
HYPEROPIA
Far-sightedness
Problem seeing close
objectsDistance between lens
and retina too small
Light focused behind
retinaCorrected with
converging lenses
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FAR-SIGHTED (HYPEROPIA)
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FOCUSING PROBLEMS
PRESBYOPIA
Form of far-
sightedness
Harder for people toread as they age
Lens loses elasticity
Corrected by glasses
with converging lenses
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FOCUSING PROBLEMS
MYOPIA
Near-sightedness
Problem seeing objects
far awayDistance between lens
and retina too large
Light focused in front
of retinaCorrect with diverging
lenses
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NEAR-SIGHTED (MYOPIA)
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DISEASES OF THE EYE
ASTIGMATISM
Eye cannot focus an
objects image on a
single point on retinaCornea is oval instead
of spherical
Causes blurred vision
Some types can becorrected with lenses
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DISEASES OF THE EYE
GLAUCOMA
Group of diseases
Affects optic nerve -
pressureLoss of ganglion cells
Gradual loss of sight
and eventual blindness
Check eyes regularly
Can be treated
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DISEASES OF THE EYE
CATARACTSClouding forms in lens
due to denaturing of
lens protein
Obstructs passage oflight
Caused by age, chronic
exposure to UV, or due
to traumaRemoved by surgery
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VISION CORRECTION
CONTACT LENSES
Artificial lens placed
over cornea
Same as glassesCorrects for both near
and far-sightedness
Also used for cosmetic
purposes (eye colour,Hollywood)
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VISION CORRECTION
LASIK
Laser Assisted In Situ
Keratomileusis.
Refractive surgeryusing laser.
Corrects near and far-
sightedness and
astigmatisms.
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Thank
You.