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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