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The Outer Layers of the Eye and Common Eyesight Issues

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  1. Unit 2 Notes: Vision Tuesday3-16-2010

  2. (1) Outer Layers of The Eye • 3 layers surrounding inner fluid: • Outermost = Sclera • Middle Tissue = Choroid • Innermost = Retina • Inner Fluid = Humor • Humor increases inner pressure • Maintains eyeball shape • Glaucoma  Increase in Pressure

  3. (2) The Sclera • White tissue on the outside • Contains the cornea: • Light enters the eye here • Directly connected to nerve endings

  4. (3) The Choroid • Made of darker pigments: • Keeps light rays inside the eye • Contains the ciliary body and the iris: • Ciliary Body = Lens is attached to this Tissue • Iris = Pigmented portion of your eye • Muscle • Contract = Decrease Light Inflow • Relax = Increase Light Inflow

  5. (4) The Retina • Contains Photoreceptors (Rods & Cones) • Electrical signal passes from receptors  optic nerve  brain • Rods = Shades & Grays • Cones = Colors • Blue-Yellow • Green • Red-Green • Impulses from multiple receptors  In Between Colors

  6. (5) Color Blindness • Monochromacy • All cones are missing or damaged • No color • Still can see shades (rods function) • Dichromacy • Red-Green Colors look the same • Blue-Yellow Colors look the same

  7. http://www.webexhibits.org/causesofcolor/2.html

  8. (6) Light Refraction & The Lens • Light passes through the cornea and Lens to enter eyeball… • Light passing thru different mediums  Refraction • Refraction = Bending of light • Eye controls amount of light entering with Iris + Lens: • Ciliary Body Contraction  Closing In of Iris  Decreased Pupil Size • Ciliary Body Relaxes  Widening of Iris  Increased Pupil Size

  9. (7) Types of Eyesight • Emmetropia = Perfect Eye Sight • Myopia = Nearsighted • Hyperopia = Farsighted • Astigmatism = All Messed Up 

  10. (8) Myopia • Cornea too convex or bulging… • Light is over focused and refracted before hitting retina • Light rays are scattered when hitting retina • Blurred Vision • Solution: • Concave Lens (thinner in middle) • Decreases refraction, Spreads out Light Rays

  11. (9) Hyperopia • Cornea is too concave (flattened out): • Light is not focused or refracted enough • Light rays are scattered when hitting retina • Blurred Vision • Solution: • Convex Lens (thicker in middle) • Refracts and Focuses light before hitting eye

  12. (10) Astigmatism • Uneven cornea or lens: • Causes blurred vision because light is refracted unevenly • Astigma = Not A Point • Solution: • Concave + Convex Lens • Cancels out Uneveness

  13. Optical / Visual Illusions • Not all are fully understood • Unusual combinations of color, shades and angles confuses our brain • Lack of “stable”, familiar surroundings confuses our brain • Our brains “fill in” areas we do not know or see to stabilize the visual

  14. Science & Perception

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  19. EYEBALLS!!! http://www.youtube.com/watch?v=y5fpJVro5NY

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