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Nervous System 2: Vision
(1) Outer Layers of The Eye
• 3 layers surrounding inner fluid:3 layers surrounding inner fluid:– Outermost = Sclera– Middle Tissue = Choroid– Innermost = Retina
• Inner Fluid = HumorInner Fluid = Humor– Humor increases inner pressure– Maintains eyeball shape– Glaucoma Increase in Pressure
(2) The Sclera• White tissue on the outside
• Contains the cornea:Contains the cornea:– Light enters the eye here– Directly connected to nerve endings
(3) The Choroid• Made of darker pigments:Made of darker pigments:
– Keeps light rays inside the eye
• Contains the ciliary body and the iris: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
(4) The Retina• Contains Photoreceptors (Rods & Cones)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
(5) Color Blindness
• MonochromacyMonochromacy– All cones are missing or damaged– No color– Still can see shades (rods function)
• DichromacyDichromacy– Red-Green Colors look the same– Blue-Yellow Colors look the same
http://www.webexhibits.org/causesofcolor/2.html
(6) Light Refraction & The Lens• Light passes through the cornea and Lens Light passes through the cornea and Lens
to enter eyeball…to enter eyeball…– Light passing thru different mediums
Refraction– Refraction = Bending of light
• Eye controls amount of light entering with Eye controls amount of light entering with Iris + Lens:Iris + Lens:– Ciliary Body Contraction Closing In of Iris
Decreased Pupil Size– Ciliary Body Relaxes Widening of Iris
Increased Pupil Size
(7) Types of Eyesight• Emmetropia = Perfect Eye Sight
• Myopia = Nearsighted
• Hyperopia = Farsighted
• Astigmatism = All Messed Up
(8) Myopia• Cornea too convex or bulging…Cornea too convex or bulging…
– Light is over-focused and refracted before hitting retina
– Light rays are scattered when hitting retina– Blurred Vision
• Solution:Solution:– Concave Lens (thinner in middle)– Decreases refraction, Spreads out Light Rays
(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
(10) Astigmatism• Uneven cornea or lens:Uneven cornea or lens:
– Causes blurred vision because light is refracted unevenly
– Astigma = Not A Point
• Solution:Solution:– Concave + Convex Lens– Cancels out Unevenness
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
Science & Perception
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