The Human Eye

Your Eyes https://youtu.be/IxAD_5X4DCg

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

Optical Illusions Optical Illusions can use color, light and patterns to create images that can be deceptive or misleading to our brains. The information gathered by the eye is processed by the brain, creating a perception that in reality, does not match the true image. Perception refers to the interpretation of what we take in through our eyes. Optical illusions occur because our brain is trying to interpret what we see and make sense of the world around us. Optical illusions simply trick our brains into seeing things which may or may not be real.

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

The Human Eye Your eyes are about to get a workout. Have you stretched your eye muscles yet? Palming- Rub hands together until warm, then cover your eyes. Eye Rolling- Sit up right, relax face, roll your eyes.

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?

What is wrong with with this sentence? Reading What is wrong with 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.

The Human Eye

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

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

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

Eye Facts 1. Eyes began to develop 550 million years ago. The simplest eyes were patches of photoreceptor protein in single-celled animals. 2. Your eyes start to develop two weeks after you are conceived. Brown eyes 6.10.14 3. The entire length of all the eyelashes shed by a human in their life is over 98 feet with each eye lash having a life span of about 5 months. 4. To protect our eyes they are positioned in a hollowed eye socket, while eyebrows prevent sweat dripping into your eyes and eyelashes keep dirt out of your eyes. 5. Your eyeballs stay the same size from birth to death, while your nose and ears continue to grow. 6. An eye is composed of more than 2 million working parts. 7. Only 1/6 of the human eyeball is exposed. 8. Corneas are the only tissues that don’t have blood. 9. The human eye weights approximately just under an ounce and is about an inch across. 10. An eye cannot be transplanted. More than 1 million nerve fibers connect each eye to the brain and currently we’re not able to reconstruct those connections.

11. 80% of our memories are determined by what we see. 12. Eyes heal quickly. With proper care, it takes only about 48 hours to repair a minor corneal scratch. 14. 80% of vision problems worldwide are avoidable or even curable. 15. Humans and dogs are the only species known to seek visual cues from another individual’s eyes, and dogs only do this when interacting with humans. 16. A fingerprint has 40 unique characteristics, but an iris has 256, a reason retina scans are increasingly being used for security purposes. 17. People who are blind can see their dreams if they weren’t born blind. 18. “Red eye” occurs in photos because light from the flash bounces off the back of the eye. The choroid is located behind the retina and is rich in blood vessels, which make it appear red on film. 19. 80% of what we learn is through our eyes. 20. Eyes are the second most complex organ after the brain.

Blind Spot 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 Transmits electrical impulses from retina to the brain Creates blind spot Brain takes inverted image and flips it so we can see

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

Sight Map 1. Light rays enter the eyes by passing through the cornea, the aqueous, the pupil, the lens, the vitreous, and then striking the light sensitive nerve cells (rods and cones) in the retina. 2. Visual processing begins in the retina. Light energy produces chemical changes in the retina's light sensitive cells. These cells, in turn, produce electrical activity. 3. Nerve fibers from these cells join at the back of the eye to form the optic nerve. 4. The optic nerve of each eye meets the other at the optic chiasm. Medial nerves of each optic nerve cross, but lateral nerves stay on the same side. The overlap of nerve fibers allows for depth perception. 5. Electrical impulses are communicated to the visual cortex of the brain by way of the optic nerve. 6. The visual cortex makes sense of the electrical impulses, and either files the information for future reference or sends a message to a motor area for action.

Video YouTube “The Human Eye” and “How the Human Eye Works” https://youtu.be/Uk0MVyFWBog

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

Far-Sighted (Hyperopia)

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

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

Near-Sighted (Myopia)

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

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

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

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

Vision Correction LASIK “Laser Assisted In Situ Keratomileusis” Refractive surgery using laser Corrects near and far-sightedness and astigmatisms