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Understanding the Outer Layers of the Eye and Common Eyesight Issues

Learn about the sclera, choroid, and retina, and how they contribute to eyesight. Discover common eyesight issues like myopia, hyperopia, and astigmatism. Explore the fascinating world of optical illusions and perception.

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Understanding 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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