The Human Eye The Human Eye n Refractive

The Human Eye

The Human Eye n Refractive index of lens different for each wavelength (colour) n Cool colours (blues) appear closer; warm colours (reds) further away n Agree?

Most people see the red, Closer than the blue. Others see the opposite. How about you?

The Human Eye n n Your eyes are about to get a workout. Have you stretched your eye muscles yet? No? Then do that now!

Are you seeing spots?

Look at the cross for 10 seconds. What do you see?

Are these lines bent…. ?

…or straight?

What shapes do you see?

Reading What is wrong with this sentence? Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Do you see the rabbit or the duck?

Read This Out Loud.

Are You Sure? Read again.

The Human Eye

Structure & Function n IRIS q q n coloured part of eye controls light entering PUPIL q q black hole in iris where light enters

Structure & Function n SCLERA q q q n whites of the eye supports eyeball provides attachment for muscles LENS q q converging lens allows us to see objects near and far

Structure & Function n CORNEA q q n transparent bulge over pupil focuses light (refracts) onto retina RETINA q q q internal membrane contain light-receptive cells (rods & cones) converts light to electrical signal

Blind Spot n n On retina where optic nerve leads back into the brain No rod or cone cells Other eye compensates for this area Try this test to prove you have a blind spot…

Close left eye and approach screen while staring at the letters…watch the dot!

Structure & Function OPTIC NERVE n Transmits electrical impulses from retina to the brain n Creates blind spot n Brain takes inverted image and flips it so we can see

Structure & Function n RODS q q q n 120 million cells detect brightness (black & white) for night vision CONES q q 6 million cells detect colour (RGB) GANGLION CELLS Detect movement and patterns

Normal Eye Focus “Blind spot”

Video You. Tube “The Human Eye” and “How the Human Eye Works” n

Focusing Problems HYPEROPIA n Far-sightedness n Problem seeing close objects n Distance between lens and retina too small n Light focused behind retina n Corrected with converging lenses

Far-Sighted (Hyperopia)

Focusing Problems PRESBYOPIA n Form of far-sightedness n Harder for people to read as they age n Lens loses elasticity n Corrected by glasses with converging lenses

Focusing Problems MYOPIA n Near-sightedness n Problem seeing objects far away n Distance between lens and retina too large n Light focused in front of retina n Correct with diverging lenses

Near-Sighted (Myopia)

Diseases of the Eye ASTIGMATISM n Eye cannot focus an object’s image on a single point on retina n Cornea is oval instead of spherical n Causes blurred vision n Some types can be corrected with lenses

Diseases of the Eye GLAUCOMA n Group of diseases n Affects optic nerve pressure n Loss of ganglion cells n Gradual loss of sight and eventual blindness n Check eyes regularly n Can be treated

Diseases of the Eye CATARACTS n Clouding forms in lens due to denaturing of lens protein n Obstructs passage of light n Caused by age, chronic exposure to UV, or due to trauma n Removed by surgery

Vision Correction CONTACT LENSES n Artificial lens placed over cornea n Same as glasses n Corrects for both near and far-sightedness n Also used for cosmetic purposes (eye colour, Hollywood)

Vision Correction LASIK n “Laser Assisted In Situ Keratomileusis” n Refractive surgery using laser n Corrects near and farsightedness and astigmatisms