2. Vision

3. The Eye Contains photoreceptors Contains accessory organs including eyelids, lacrimal apparatus, and muscles

4. Eye Structure The eye is a hollow round structure, filled with fluid The outermost part is the cornea, a transparent tissue that bulges out in front

5. Eye Structure Sclera is the white portion of the eye Light passes through the cornea, then through the pupil (opening), and then through the lens Lens can change shape to focus light rays on the back of the eye

6. Eye Structure The iris is the colored part of the eye It closes around the pupil in bright light, and pulls back in dim light The pupil does not really change size

7. Eye Structure There are two bodies of fluid First, the aqueous humor is between the cornea and the lens Second, the vitreous humor fills the large part of the sphere between the lens and the retina

8. Eye Structure The retina lines the back of the eye It contains the photoreceptors Two types: rods and cones The fovea centralis (focal point) produces the sharpest vision

9. Eye Structure

10. Rods have long thin projections, and are more sensitive to light than are cones Rods provide outlines of images and see black and white, and in dim light Cones provide sharp images, and see color cone rod

11. Eye Structure

12. The optic nerve leaves from the back of the retina to travel to the brain Where the optic nerve interrupts the retina, there are not rods and cones This is the blind spot

13. Eye Problems Near sightedness (myopia): can see near, not far Far sightedness(hyperopia): can see far, not near Astigmatism: uneven cornea cannot send light rays to one focal point

14. Eye Problems Glaucoma: excess aqueous humor collects inside Causes dangerously high pressure Colorblindness: missing one or more kind of cones Cataracts: gradual clouding of lens

15. Cataracts