ANATOMY Unit 2 Notes: Vision

(1) The Layers & Humor 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 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: Pupil: The outer covering of the eye. Its shape determines your eyesight. Pupil: Gaping hole in the center of the eye. Looks like a dark circle/dot in the center. Allows light to enter the eye.

(3) The Iris and Lens Iris: Lens: 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 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 Monochromacy Dichromacy All cones are missing or damaged Can see no color Still can see shades (rods function) *Like black and white television. Dichromacy 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

(6) Light Refraction Refraction: Light rays bend every time they pass through a different medium. Light must pass through your: Cornea Lens Humor The light rays need to be concentrated at one specific point, directly on the back of 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… Solution: 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: 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): Solution: 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: Solution: 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: Use a lens which is both concave and convex in proper locations. The lens will concentrate and spread out the light rays appropriately.