light & sight

7/27/2019 Light & Sight

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LIGHT & SIGHT


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What is light?

Light comes in two forms

as WAVES or PARTICLES(photons).

Light must be produced by

a source, but it is thereflection of light thatenables us to see objects.

Where light is blockedfrom reflecting it producesshadows which are theabsence of light, as isdarkness.


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How do we see?

The human eye is a complexsystem that records light andturns it into an electrical

signal which is interpreted bythe brain.

The different parts of thehuman eye function together

to produce an image. If oneof these parts is damaged,then we are unable to see.


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The Human Eye

The eye is divided

into parts whichcontrol the entry of

light or capture it to

send to the brain


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The Pupil and Iris

The iris is a ring ofmuscle around avariable size openingwhich is the pupil.

The iris consists ofconcentric muscleswhich contract andrelease to make thepupil smaller or larger.

The pupil itself looksblack because it is ahole.


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The Lens

The lens is a fluidfilled structure thatfocuses light fromthe cornea on the

retina. The lens is held in

place by ligamentswhich areconnected to the

ciliary muscles.These can alter thelens shape, calledaccommodation.
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Short or Long Sightedness

Sometimes there is aproblem with the lens thisleads to long sightedness(can see far but not near)and short sightedness (can

see close but not far). Glasses account for the

inability of the lens to focuscorrectly and allow theperson to see clearly. A

convex lens will correct longsightedness and a concavelens will correct shortsightedness.


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The Interior of the Eye

The eye is surrounded by a tough membrane

which hold the shape of the eye in

conjunction with the vitreous humour which is

a thick gel-like water based substance which

gives the eye structure by putting pressure on

the external membrane. The eye is lined with

another membrane called the retina.


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The Retina

The retina is the lining of the eye. Itis rich in blood vessels which form apattern unique to each humanbeing.

The retina is covered in specialised

cells called the rods and cones,which are different types ofphotoreceptors.

There are two specific features onthe retina the fovea and macula.

The macula is the central point offocus and allows us to see detail.

The fovea is completely free ofrods.


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Rods and Cones

Rods are necessary

for peripheral vision

and seeing in dim

light.

Cones are necessary

for direct sight and

seeing in bright light.


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The Optic Nerve

The optic nerve takes the invertedimage from the retinal receptorsand converts it into an electricalsignal. This is sent via the nervecells in the optic nerve to the brain

which translates and turns theimage the right way round.

Where the optic nerve comes intothe eye we have a blind spot. Thiscompensated for as our two eyeswork in conjunction with each

other to produce a threedimensional image.


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Stereoscopic Vision

Humans have stereoscopic

vision as we have two eyes

that function together.

Each image from each eye is

seen simultaneously and

processed simultaneously into

a single image. This gives usout depth perception and

awareness of 3D objects.


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Try It!

Place one hand over each eye in turn and

notice where the blind spot is.

Try closing one eye and try to grasp an object

that is close to you. Now try one far from you.

Get someone to approach you from behind

and at an angle. See how much you can see.


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Optical Illusions

Because of our depth perception, our eyes can

be tricked. Try looking at these images and see

what happens.


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