Anatomy unit 2 nervous system vision notes

ANATOMY

Unit 2 Notes: Vision

(1) The Layers & Humor• There are 3 layers of tissue:There are 3 layers of tissue:

– Sclera = White outer tissue– Retina = Tissue in between Sclera + Choroid– Choroid = Dark tissue on the inside cavity

*The choroid helps keep light inside the eye.

• Humor = Fluid Inside the EyeHumor = Fluid Inside the Eye– Humor increases inner pressure– Maintains eyeball shape– Glaucoma is caused by the inability to recycle

humor, increasing pressure and preventing vision.

(2) The Cornea and Pupil• Cornea:Cornea:

– The outer covering of the eye.The outer covering of the eye.– Its shape determines your eyesight.Its shape determines your eyesight.

• Pupil:Pupil:– Gaping hole in the center of the eye.Gaping hole in the center of the eye.– Looks like a dark circle/dot in the center.Looks like a dark circle/dot in the center.– Allows light to enter the eye.Allows light to enter the eye.

(3) The Iris and Lens• Iris:

– The colored ring in the eye.– Contracts and relaxes to control amount of light

entering the eye.– Contract = Gets Smaller = Decreases light when

bright outside.– Relax = Gets Bigger = Increases light when dark

outside.

• Lens:– Hard structure behind cornea and iris.– Helps focus and refract light to the retina.

(4) The Retina• Contains the photoreceptors that allow your Contains the photoreceptors that allow your

brain to pick up on colors/shapes/shades.brain to pick up on colors/shapes/shades.

• 2 Types of Photoreceptors:– Rods = Pick up on Shades & Grays– Cones = Pick up on Colors

• Blue-Yellow• Green• Red-Green

(5) Color Blindness

• MonochromacyMonochromacy– All cones are missing or damaged– Can see no color– Still can see shades (rods function)

*Like black and white television.

• DichromacyDichromacy– Pairs of cones are damaged, making it difficult

to differentiate between pairs of colors.• Red-Green Colors look the same• Blue-Yellow Colors look the same

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

(6) Light Refraction• Refraction:Refraction:

– Light rays bend every time they pass through a Light rays bend every time they pass through a different medium.different medium.

– Light must pass through your:Light must pass through your:• CorneaCornea• LensLens• HumorHumor

• The light rays need to be concentrated at The light rays need to be concentrated at one specific point, directly on the back of one specific point, directly on the back of the retina for accurate vision.the retina for accurate vision.

(7) Types of Eyesight• Emmetropia = Perfect Eye Sight

• Myopia = Nearsighted

• Hyperopia = Farsighted

• Astigmatism = Nearsighted + Farsighted

(8) Myopia• Cornea is too convex or bulging…Cornea is too convex or bulging…

– Light is over focused and refracted before hitting retina.

– Light rays are scattered by the time they hit the retina.

– Results in blurred vision.

• Solution:Solution:– Use a Concave Lens (thinner in middle)– Spreads out light rays, decreases refraction so

rays are concentrated right at retina.

(9) Hyperopia• Cornea is too concave (flattened out):

– Light is under-focused.– Light rays are still scattered by the time they hit

the retina.– Results in blurred vision.

• Solution:– Use a Convex Lens (thicker in middle)– Concentrates the light rays, so that they hit at

one point on the retina.

(10) Astigmatism• Uneven cornea or lens:Uneven cornea or lens:

– Astigma = Not A Point– Cornea is too flat in one spot, and too bulging in

another.– Results in blurred vision, and splitting of

images.

• Solution:Solution:– Use a lens which is both concave and convex in

proper locations.– The lens will concentrate and spread out the

light rays appropriately.