Human vision

What lens do humans have

Convex lens that can adjust its focal length by changing the shape of the tiny ring of muscles it’s attached to

When ciliary muscles contract

Lens becomes more spherical and thicker

Increasing amount of refraction and shortened focal length

Makes eyeballs able to focus on nearby objects

What lens do humans have

Convex lens that can adjust its focal length by changing the shape of the tiny ring of muscles it’s attached to

When ciliary muscles contract

Lens becomes more spherical and thicker

Increasing amount of refraction and shortened focal length

Makes eyeballs able to focus on nearby objects

When ciliary muscles relax

Lens becomes more flat and thinner

Increase focal length

Allows eye balls to focus on distant objects.

Rod cells

Dectet shape and movement in low lights

Can only detect shades of grey

Located in peripheral region of the retina

Cone cells

Photosector cells that can detect colors

3 types that each r sensitive to a certain primary color (green blue and red)

Found in center region of the retina

Blind spot

Where optic nerve connects eye to brain

No photoreceptor cells (cannot detect light)

Brain uses information about surrounding nearby the retina

Correction vision promblems

Hyperopia (far sighted)

Myopia (near sighted)

Astigmatism (no clear image in retina)

Presbyopia (old age)

Hyperopia

Can see distant objects

Can’t see nearby objects

Converging lens helps to correct promblem

Eyeball is to short

Image forms behind retina

Myopia

Diverging lens helps to correct promblem

Cannot see distant objects

Can see nearby objects

Image forms infront of lens

Eyballl is to long

Astigmatism

Eye can not form clear image in retina

Cornea is a irrigular shape

Correct with a toroidal lens which had 2 focal points

Presbyopia

Age related

Lens harderns and becomes less fleixable

Ciliary muscles become weaker

Adding converging lens (+) helps to correct promblem.