the human eye day 18

7/26/2019 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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SCLERAwhites of the eyesupports eyeballprovides

attachment formuscles

LENS

converging lensallows us to seeobjects near and far


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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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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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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.

the human eye day 18

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