1. The Human Eye Sight most important sense in humans 80% of info from reading, TV, video, and the world around us

2. Structure of the Eyeball Figure 15.4a

3. EYE Eyelid: protective cover, wets surface

5. Extrinsic Eye Muscles Figure 15.3a, b

6. Lacrimal Apparatus Figure 15.2

7. Structure of the Eyeball A slightly irregular hollow sphere with anterior and posterior poles A slightly irregular hollow sphere with anterior and posterior poles The wall is composed of three tunics – fibrous, vascular, and sensory The wall is composed of three tunics – fibrous, vascular, and sensory The internal cavity is filled with fluids called humors The internal cavity is filled with fluids called humors The lens separates the internal cavity into anterior and posterior segments The lens separates the internal cavity into anterior and posterior segments

8. 3 layers Sclera: tough outer layer, “white” of the eye; shape; protection Sclera: tough outer layer, “white” of the eye; shape; protection Cornea: clear layer at front of eye; protection; light enters through Cornea: clear layer at front of eye; protection; light enters through Choroid coat: just inside sclera; dark brown to stop reflection; contains many blood vessels Choroid coat: just inside sclera; dark brown to stop reflection; contains many blood vessels

9. Aqueous humor Watery fluid between cornea and lens Watery fluid between cornea and lens Begins refracting (bending) light Begins refracting (bending) light

10. Pupil An opening into the eye An opening into the eye Light enters through here Light enters through here Size controlled by iris Size controlled by iris Dark because the inside of the eye is dark Dark because the inside of the eye is dark “redeye”---light bounces off blood vessels in retina “redeye”---light bounces off blood vessels in retina

11. Iris Front of choroid layer Front of choroid layer muscular; changes to control amount of light entering eye muscular; changes to control amount of light entering eye In bright light-iris is large; pupil is small; less light comes in In bright light-iris is large; pupil is small; less light comes in In low light- iris small; pupil large; more light enters eye In low light- iris small; pupil large; more light enters eye

12. Color of iris determined by amount of melanin, a pigment *lots of melanin=brown *very little or none=blue

13. Lens Clear, flexible structure which refracts (bends) light onto the retina Clear, flexible structure which refracts (bends) light onto the retina Special muscles (ciliary) attach to lens Special muscles (ciliary) attach to lens hold lens in place pull on lens to slightly change its shape to help focus

15. Lens refracts or bends light; focal point is where rays cross

16. Image formed on the retina is inverted, upside down; the brain “turns” it right side up

17. Retina Layer of specialized cells Layer of specialized cells Where image from lens is formed Where image from lens is formed Cells convert image into electrical impulses which travel through the optic nerve to the brain Cells convert image into electrical impulses which travel through the optic nerve to the brain

18. Specialized cells Rods: sensitive to weak light but not to color ; allows vision in dim light but not in color Rods: sensitive to weak light but not to color ; allows vision in dim light but not in color Cones: sensitive to color but only in adequate light Cones: sensitive to color but only in adequate light cones for red, green, and blue 125 million rods 6.5 million cones

20. Sensory Tunic: Retina Figure 15.6a

21. Vision Light sensitive pigment: retinal made from vitamin A Light sensitive pigment: retinal made from vitamin A Not enough vitamin A = night blindness Not enough vitamin A = night blindness Combines with proteins in rods and cones (protein are different in each type) Combines with proteins in rods and cones (protein are different in each type) Light breaks the bond and sends an electrical impulse down nerve Light breaks the bond and sends an electrical impulse down nerve

22. Optic Nerve Nerve fibers from rods and cones join together to make up the optic nerve Nerve fibers from rods and cones join together to make up the optic nerve Carries the impulse to the brain Carries the impulse to the brain Point where the optic nerve leaves the eye has no rods or cones……blind spot Point where the optic nerve leaves the eye has no rods or cones……blind spot

25. Vision center of the Brain Back of the brain…..occipital lobe Back of the brain…..occipital lobe Turns the image we see right side up and into 3-D Turns the image we see right side up and into 3-D Enables us to interpret what we see Enables us to interpret what we see Can be fooled…….optical illusions, eye witness accounts Can be fooled…….optical illusions, eye witness accounts

26. Occipital Lobe

27. Common Eye Problems Each year over 1 million eye injuries Each year over 1 million eye injuries Most could be prevented Most could be prevented

28. Prevent Eye Injuries Wear goggles when: Wear goggles when: Jump starting a car Jump starting a car Mowing, edging, other lawn power tools Mowing, edging, other lawn power tools Using power tools Using power tools Using chemicals such as chlorine, ammonia, bleach and paint solvent Using chemicals such as chlorine, ammonia, bleach and paint solvent Regular glasses are NOT enough

29. Prevent Eye Injuries in Sports 40,000 injuries a year 40,000 injuries a year Use batting helmets with face shields Use batting helmets with face shields Polycarbonate safety goggles for racquet ball, basketball Polycarbonate safety goggles for racquet ball, basketball Helmets and face shields approved by US Amateur Hockey Association when playing hockey Helmets and face shields approved by US Amateur Hockey Association when playing hockey

30. Other precautions Don’t play with fireworks Don’t play with fireworks Wear sunglasses that block at least 90% of UVA and UVB rays Wear sunglasses that block at least 90% of UVA and UVB rays Welding masks when using such equipment Welding masks when using such equipment Never let young kids have toys like darts and BB guns Never let young kids have toys like darts and BB guns Workplace: wear whatever safety goggle or eye protection is recommended at all times Workplace: wear whatever safety goggle or eye protection is recommended at all times

31. Other eye diseases Diabetic retinopathy: causes retina to degrade, causes blindness if diabetes is not treated Diabetic retinopathy: causes retina to degrade, causes blindness if diabetes is not treated Cataract: cloudy lens due to protein deposits; very common as we age correctable with surgery, replace old lens with a plastic lens Cataract: cloudy lens due to protein deposits; very common as we age correctable with surgery, replace old lens with a plastic lens

32. Conjunctivitis or “pink eye”: irritation of the covering of eye caused by virus, bacteria, should see a doctor because only certain medicines ok for eyes…..if caused by contacts…do NOT put them back in until ok’d by dr Conjunctivitis or “pink eye”: irritation of the covering of eye caused by virus, bacteria, should see a doctor because only certain medicines ok for eyes…..if caused by contacts…do NOT put them back in until ok’d by dr

33.  Glaucoma: pressure in eye damages optic nerve; easy to detect with eye check up, painless  Macular degeneration: spot on retina that sees clear, crisp images in center of field of vision; most common cause of blindness in the world

34. Retinal detachment Often after a blow to the head but can be spontaneous Often after a blow to the head but can be spontaneous Flashes of light and “floating” spots Flashes of light and “floating” spots Need to see doctor immediately Need to see doctor immediately

35. Vision Problems Myopia or nearsightedness: cannot see far away Myopia or nearsightedness: cannot see far away Caused by elongated eyeball which causes image to fall before retina Caused by elongated eyeball which causes image to fall before retina

37. Problems of Refraction Figure 15.14a, b

38. Presbyopia or farsightedness: cannot see near, usually comes with age Presbyopia or farsightedness: cannot see near, usually comes with age

39. Astigmatism: irregular curvature of cornea or lens Astigmatism: irregular curvature of cornea or lens

40. Color blindness color vision deficiency Genetic, carried on X chromosome Genetic, carried on X chromosome Most often in males Most often in males Usually red/green deficit Usually red/green deficit