Unit 2 Notes:Vision

(1) Layers of Tissue in the Eye● Outermost Layer →

“Sclera” (White external tissue).

● Middle Layer → “Retina” (contains the photoreceptors to pick up on light).

● Innermost Layer → “Choroid” (Dark tissue used to help keep light inside the eye).

(2) The Humor● The humor is the goo-like fluid inside the eye.

● Helps maintain proper density and pressure inside the eye, and maintain eyeball shape.

● Glaucoma is caused by the inability to recycle humor, increasing pressure and preventing proper retinal transmission.

(3) The Cornea● The cornea is the outer-covering of the eye.

● The shape of the cornea determines your eyesight.

(4) The Iris and Pupil● The Iris →

○ Colored ring.○ Controls the amount of light that enters the eye.○ Contraction = Tightening of opening = Decrease light entering○ Relaxation = Increase in opening size = Increase light entering

● The Pupil →○ Gaping hole in the center of the iris.○ Looks like a black circle / dot in the center of the eye.○ Allows light to enter the eye.

(5) The Retina● The Retina is the layer of tissue containing photoreceptors.

● Photoreceptors allow your brain to pick up on colors, shapes, and shades.

● 2 Types of Photoreceptors:○ Rods → Pick up on Shades and Grays○ Cones → Pick up on Colors

(6) Retinal Damage & Color Blindness● When cones are not properly developed in the retina, this leads to color

blindness.

● Monochromacy:○ Occurs when all cones are missing or damaged.○ Person cannot see any color.○ Person can still see shades (rods function perfectly fine).

● Dichromacy:○ Occurs when pairs of cones are missing or damaged.○ Person has difficulty distinguishing between pairs of colors.○ Person can still distinguish shades fine.

(7) Light Refraction & The Lens● Light Refraction:

When light rays bend as they pass through different mediums.

● Light must pass through 3 different mediums in your eye:○ Cornea○ Lens○ Humor

● The lens helps to properly refract and focus the light rays.

● Light rays need to be concentrated at one specific point at the back of the retina for accurate vision.

(8) Types of Eyesight● Emmetropia = Perfect Eyesight

● Myopia = Nearsighted

● Hyperopia = Farsighted

● Astigmatism = Nearsighted + Farsighted

(9) Myopia (Nearsighted)● Cause:

○ Cornea is too curved or bulging.○ Light is over focused and refracted before hitting the retina.○ Light rays scatter before hitting the retina.○ Scattered light = blurred vision.

● Solution:○ Put a thin lens in front of the cornea.○ The thin lens will spread out the light rays more.○ Decreases refraction so light rays are concentrated when hitting retina.

(10) Hyperopia (Farsighted)● Cause:

○ Cornea is too flat.○ Light is under focused and refracted before hitting the retina.○ Light rays scatter before hitting the retina.○ Scattered light = blurred vision.

● Solution:○ Put a thick lens in front of the cornea.○ The thick lens will concentrate the light rays more.○ Increases refraction so light rays are concentrated when hitting retina.

(11) Astigmatism● Cause:

○ Cornea is flattened in one area, and bulging in another area.○ Light is under and over focused in the different areas, before hitting the retina.○ Light rays scatter before hitting the retina.○ Scattered light = blurred vision.

● Solution:○ Put a lens which has a thick region, and a thin region, in front of the cornea.○ The thick area will concentrate the light rays more, the thin area will spread out the

light rays as needed.