Minds-on

The Human Eye

The Eye vs. the CameraThe Eye The Camera

Opens and closes to adjust the amount of light that enters

The Iris The diaphragm

The Eye vs. the CameraThe Eye The Camera

The opening where light enters

The pupil The Aperture

Dilated pupil: when in dim light

Constricted pupil: when in bright light

The Eye vs. the CameraThe Eye The Camera

Refract light to form a smaller, sharp image

The lens and cornea

The lens

The Eye vs. the CameraThe Eye The Camera

Surface where the image is created

retina Film or digital sensor

Photoreceptor cells on Retina- Rod cells: detect object in low light; we see shades of grey- Cone cells: detect colors

The Cornea-lens combination concentrates light to form a smaller, inverted and real image on the retina.

How the Brain ‘Sees’

Any question at this point?

Electrical impulses from the retina travel through the optical nerve to the brain, where

the image is flipped so we ‘see’ upright.

Accommodation: Changes the focal length of the lens by changing the lens shape(using eye

muscles) so that both close and distant objects can be seen clearly.

Focusing Problems

Hyperopia (Far-Sightedness)Disability: can’t focus near

objects.Cause: eyeball is too shallowImage forms: beyond retinaCorrect with: A converging lens

The converging lens, causes the light rays to intersect sooner so that the image focuses on the retina instead of beyond the retina.

A positive meniscus is a thinner converging lens used in glasses.

Focusing ProblemsMyopia (Near-Sightedness)Disability: can’t focus

distant objects.Cause: eyeball is too

deepImage forms: in front of

retinaCorrect with: A diverging

lens

The diverging lens, causes the light rays to intersect later so that the image focuses on the retina instead of in front of the retina.

A negative meniscus is a thinner diverging lens used in glasses.

Focusing ProblemPresbyopiaDisability: can’t focus near

objects (small print) due to poor accomodation.

Cause: aging lens is less elastic, eye muscles are weakerLens does not thicken enoughImage forms: beyond retinaCorrect with: A converging lens

for reading

For Presbyopia:The converging lens, causes the diverging light

rays (from close objects) to intersect sooner so that the image focuses on the retina instead of beyond the retina.

Other Focusing Problems

Astigmatism

Colour Blindness

Cataracts

Cataract = a medical condition in which the lens of the eye becomes progressively opaque, resulting in blurred vision.

Tunnel Vision

a condition in which you can see things that are straight ahead of you but not to the side (i.e. loss of peripheral vision)

Eye blood vessels burst