1. VISION

2. VISION
Your eyes are the sense organ that enables you to see the objects in your environment.
Your eyes respond to the stimulus of light. They convert that stimulus into impulses that your brain interprets, enabling you to see.

3. PARTS OF THE EYE

4. PARTS OF THE EYE LENS – Behind the pupil, focuses and bends the light
RETINA – Layer of receptor cells (rods and cones) that line the back of the eye.
OPTIC NERVE – Sends nerve impulse from retina to the cerebrum
CORNEA- Clear tissue that covers the front of the eye.
PUPIL – Opening through which light enters the eye.
IRIS – Circular structure that surrounds the pupil, regulates the amount of light that enters the eye.

5. HOW LIGHT ENTERS THE EYE
1. Rays of light pass through the CORNEA.
2. Rays of light pass through the PUPIL.
3. The IRIS adjusts how much light is let through the PUPIL.
In bright light the Iris becomes smaller
In dim light the Iris becomes larger

6. HOW LIGHT IS FOCUSED
4. The light that passes through the PUPIL strikes the LENS.
5. The LENS focuses and bends the light rays into an upside down image onto the RETINA.

7. HOW TO SEE AN IMAGE 6. The light from the LENS strikes the RETINA.
7. Receptors (rods and cones) on the retina respond to the light.
RODS  Work best in dim light, help see black, white, and gray
CONES  Work best in bright light, help you see colors

8. HOW TO SEE AN IMAGE
8. When light strikes the rods and cones, nerve impulses begin.
9. Nerves impulses travel to the cerebrum through OPTIC NERVES.
10. The cerebrum combines images from both the right and left eye and flip the image right-side up.

9. VISION PROBLEMS
The LENS is a curved, transparent object that bends light rays as they pass through it.
If the lens does not focus light properly on the retina, vision problems result.
The lenses in eyeglasses can help correct the vision problems.

10. NEARSIGHTEDNESS See nearby objects clearly.
Cannot see objects far away.
Caused by an eyeball that is too long.
Because of the extra length the light must travel further to reach the retina, making distance objects not focus clearly.
Image comes into focus in front of the retina

11. CORRECTING NEARSIGHTEDNESS
To correct nearsightedness a person wears eyeglasses with concave lenses.
Spreads the light rays out making them focus on the retina, not before it.

12. FARSIGHTEDNESS See distant objects clearly. Cannot see objects nearby.
Caused by an eyeball that is too short.
Because the eye is so short, the light wants to travel to far past the retina. When the light hits the retina the image looks blurry.

13. CORRECTING FARSIGHTEDNESS
To correct farsightedness a person wears eyeglasses with convex lenses.
The lens makes the light rays bend toward each other quicker helping them focus on the retina.

15. OPTICAL ILLUSIONS