12.3– The Human Eyepg. 506 - 511

The Eyeball

The Eye by Bill Nye

Iris: coloured part of the eye that opens and closes to let in more or less light. In the centre you find the pupil

Pupil: opening where light enters the eye Cornea: Transparent bulge on top of the

pupil

Eye Anatomy

Lens: Clear part behind the iris◦ NOTE: Both the cornea & lens focus light &

cause it to converge on the back of the eye. Retina: Inner lining of eye that is made of

light-sensitive cells, called rods and cones. These cells receive light rays, process them & send electric signals to the optic nerve

Eye Anatomy

Optic Nerve: The nerve at the back of the eye that is attached to the retina. It transmits the electrical impulses from the retina to the brain◦ Since there are no light sensitive cells here, it

creates a blind spot but each eye compensates for the other

Eye Anatomy

Light entering our eyes is refracted The lens acts like a converging lens that

produces a smaller, real, inverted image on the retina.

Electrical impulses travel through the optic nerve to the brain

Brain flips the inverted image so what we see is upright

Human Vision

Accommodation is the changing of shape of the lens by ciliary muscles to allow a sharp focused image to form on the retina

By changing the eye’s shape, the focal length changes, allowing us to focus on distant and nearby objects

Accommodation

Accommodation does not always work well. This results in an inability to focus on objects and thus producing blurred vision

Focusing Problems

Inability to focus light from nearby objects (can see distant objects)

Light is focused behind the retina Caused by a thin cornea; or an eyeball that

is too short

Hyperopia (far-sightedness)

Corrected using converging contact lenses or eye glasses to help refract the light

A modified form of the converging lens, called a positive meniscus is used because it is thinner & more visually appealing than a basic converging lens

Hyperopia (far-sightedness)

Form of far-sightedness caused by a loss of accommodation as a person ages

Eye loses its elasticity as we grow older Corrected using glasses with converging

lenses

Presbyopia

Inability of the eye to focus light from distant objects (can see nearby objects)

Light is focused in front of the retina A modified form of the diverging lens, called

a negative meniscus, is used

Myopia (near-sightedness)

blurred or distorted vision

caused by an incorrectly shaped cornea

corrective lenses or laser eye surgery can be used to correct astigmatism

Astigmatism

Read pg. 506 - 511 Do #5, 7, 8 on pg. 511 Study for your Physics Unit Test (Chapters 10, 11, 12)

Homework