Lenses and Our Eyes

Lenses convex lens – thicker in middle, thinner at edge concave lens – thinner in middle, thicker at edge

Lenses light passing through a convex lens gets closer together or CONVERGES to a single FOCAL POINT light passing through a concave lens spreads out or DIVERGES

The Eye your eyes are lenses light enters through the pupil the cornea is a protective covering over the pupil

the iris is a muscle around the pupil that contracts and relaxes to allow different amounts of light through the iris is the part of your eye with colour

behind the pupil is the lens of your eye its flexible like rubber convex in shape and small… about the size of your small fingernail the ciliary muscles can work to slightly change the shape of the lens to help you focus the eye is filled with vitreous humour – a liquid that keeps the eyeball from collapsing

Images images come into the eye through the lens and are projected onto the retina UPSIDE DOWN your brain then knows to process the image right side up

Where’s your blind spot? complete the activity Figure 3.37 page 217 of your text book

Blind Spot when the retina senses light, small electrical impulses are produced these impulses travel along the optic nerve from the eye to the brain the point where the optic nerve enters the retina does not have any light-sensing cells… and this point is known as the blind spot

Your eye is like a camera the aperture or opening of the camera is like the pupil of the eye the diaphragm of the camera opens and closes the aperture like the iris of the eye the lens focuses the image onto the film of a camera… like the lens focuses an image onto the retina of the eye

What happens when the lens does not focus properly? distant objects hard to see close objects hard to see

if your lens is a bit to convex it focuses images before the retina you are near sighted and can only see things clearly if they are close up the solution is glasses with a concave lens if your lens is not convex enough then it focuses images farther than the retina you are far sighted and can only see things clearly if they are far away the solution is glasses with a convex lens

Test Your Vision

What about other eyes dogs dinosaurs

fish have rounded eyes that bulge out so they can see in practically every direction birds have better eyesight that humans because they are sensitive to more light wavelengths hawks can see 8 times better than us nocturnal animals (like owls) have huge pupils to let in lots of light… so they can see at night insects have compound eyes, with lots of lenses, so they can easily spot movement