Senses- The EyeThe human eye is the organ which gives us

the sense of sight, allowing us to learn more about the surrounding world (environment) than we do with any of the other 4 senses.

The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit.

The eye is able to see in bright light or in dim light, but it cannot see objects when light is absent.

The eyes are about 1 inch in diameter.

What percent do you think we learn from our sense of sight?Research has said that 80%-85% of

everything we know comes from our sense of sight.

The Eyes built in Protection1. Lacrimal Gland- is responsible for producing tears

Tears have salt and mucus to help fight germs.Wash foreign objects out of the eyes. Keep eyes moist.

2. Eyebrows- growths of hair that protect the eyes from foreign particles, sweat, and direct rays of light.

3. Eyelids- folds of skin that protect the eye by covering its surface.

4. Eyelashes- help to keep foreign particles out of the eye.

5. Orbital bones- eye sockets for protection

Anatomy (Parts) of the EyeLayers of the Eye (3)

1. Sclera- tough outer layer of the eye Gives the eye its round shape. This is the white of the eye.2. Choroid- middle layer of the eye Contains the blood vessels that nourish the eye.3. Retina- innermost layer of the eye Contains nerve cells responsible for vision. (rods, cones)

Anatomy (Parts) of the EyeOuter to Inner1. Cornea- round, clear dish in which light passes to

the lens. Very sensitive with many nerve endings.2. Aqueous Humor- space between cornea and lens

that is filled with watery substance (cleans lens).

3. Iris- colored part of the eye. Controls the amount of light let in.

3a. Ciliary Muscles- control movement of the iris. (bigger, smaller).

4. Pupil- black circle in the center of the iris. Light continues to lens.

Anatomy (Parts) of the Eye5. Lens- forms and focuses images on the retinal wall5a. Suspensory Ligaments- pull and relax the lens for

focusing.6. Vitreous Humor- jelly-like fluid that gives the eye its

shape.7. Retina- acts as a movie screen for the light.8. Rods- located behind the retina. They register light and

darkness. Also contain visual purple (light to dark room) 125 million.

9. Cones- give you vision in bright light and are able to detect differences in color. 7 million.

10. Optic Nerve- carries light messages to brain for processing

How suspensory ligaments work

So How Do We See?Light passes through the:CorneaAqueous HumorPupilLens (bulges-close, flattens-far)Vitreous HumorRetina (images are upside down)Rods, Cones (light, dark, color)Optic Nerve (to brain)Brain (flips images and learn or recalls)

Muscles of the eye

1. Superior oblique- rotates eye2. Superior rectus- raises eye3. Lateral rectus- moves eye away from nose4. Medial rectus- moves eye toward nose5. Inferior oblique- rotates eye6. Inferior rectus- lowers eye

Problems with Vision

Nearsightedness (myopia)- able to see near, but blurry from a distance. Images are focused in front of retina. Fixed with concave lenses to push images further back on retinal wall.

Normal Myopia

Farsightedness (hyperopia)- able to see distant objects clearly, but close up is blurred. Images focused beyond retina. Fixed with convex lenses to bring images forward on retinal wall.

Astigmatism- curvature of the cornea is uneven. Light rays focus at different points (ghosting)

Cataracts- clouding of the lens. Causes blurring, hazy or problems with night vision.

Strabismus- eye muscles of both eyes do not work together, causing one or both eyes to turn inward or outward

Glaucoma- fluid pressures increasing in the eyeball, which may cause damage to the optic nerve and can cause blindness.

Conjunctivitis- an inflammation of the conjunctiva (pink eye)

Everyone has a blind spot!Draw a square on the left side of your paper.Now draw a circle on the right side about 6in.

from the square.Close your left eye.Hold your paper at arms length and SLOWLY

bring it towards you while just staring at the square.

What happened to the circle?