Human VisionOutcome C4 – Explain how human vision works

The human eye– Sclera – white tissue surrounding our cornea– Iris – the muscle which contracts and dilates

our pupil– Pupil – the opening which allows light into our

eye

The human eye– Cornea – a transparent tissue which covers our

pupil and iris. It’s job is to refract light

– Retina – Region in the back of our eye where images are formed

– Lens – Convex lenses in our eye refract and focus light onto our retina

– Optic Nerve – Nerve tissue which sends signals to our brain

How the parts of our eye work together– Light enters through our pupil and into our eye. The

amount of light that enters our eye is controlled by the Iris

– For an image to form correctly, the light is first refracted by our cornea and refracted again by our lens

How the parts of our eye work together– Focusing of the image is done by tiny muscles, that

can change the shape of our lens

How the parts of our eye work together– The refracted light then forms an image on our

Retina– Our retina is a light sensitive layer inside our eye– Little cells called Rod cells are sensitive to

the level of light (dim or bright)– Little cells called Cone cells are sensitive to

colour

– The level of light and colour detected by rods and cones are sent as electrical signals down the optic nerve and to our brain

– Where the optic nerve is, there is a blind spot

The Cornea-Lens-Retina system– This is the system used to describe the formation of

images in the human eye

– Steps:1. Light rays coming from its source is

primarily focused by the cornea (via refraction)

2. This light continues on through our lens which does the fine focusing (via refraction again)

3. The light rays will then converge on our Retina forming an (inverted) image

The Cornea-Lens-Retina system– Fine focusing of images are done by the contracting

and relaxing of muscles surrounding our lens.

– Distant objects require a “thinner” lens to focus. So muscles surrounding the lens will relax and the lens will flatten out

– Close objects require a “thicker” lens to focus. So muscles surrounding the lens will contract and the lens will become thicker

Drawing of a thick and thinner lens

Common vision problems– Near-sightedness – people can see nearby objects

clearly, but not far away objects– Problem: Light rays converge in front of the

Retina

– Solution: Wearing glasses that have concave lenses will refract the light enough such that the light rays will converge on the retina

Common vision problems– Far-sightedness – people can see far away objects

clearly, but not nearby objects– Problem: Light rays converge behind the retina

– Solution: Wearing glasses that have convex lenses will refract the light such that the light rays will converge on the retina

Correcting and extending vision– Modern technology can now use laser surgery to

correct vision. It reshapes the cornea

– What are some things that can “extend” our vision?

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Similarities and differences in eyes and other optical systems

Telescopes

TURN TO YOUR PARTNER (TTYP)– Question: Using the figure provided to you, answer:

– Wavelengths longer than visible light include?????

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– Wavelengths shorter than visible light include?????

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Electromagnetic radiation– How are these different?– TURN TO YOUR PARTNER AND ANSWER:

– What 3 differences do specific electromagnetic radiation have from one another… For example: Contrast UV rays to Radiowaves

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