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Lecture # 18

Lecture # 18. Retinal disease 4 / 4/13. QUIZ on Tuesday. 20 minutes at end of class 10 points added to midterm grade (up to total of 100) Bring your calculators. Animal Wiki due midnight tonight. Keep it simple

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Lecture # 18

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  1. Lecture #18 Retinal disease 4/4/13

  2. QUIZ on Tuesday • 20 minutes at end of class • 10 points added to midterm grade (up to total of 100) • Bring your calculators

  3. Animal Wiki due midnight tonight • Keep it simple • If you can’t find out any color vision info make your best guess based on similar organisms • Be sure to try some wiki formatting (bullets or colors, adding links)

  4. Final wiki project • Topic of interest to you • Introduction page • State topic • Why is it interesting / important? • Give brief introduction or background • 3 topic pages • Draw on primary literature • Each 500-1000 words • Make interesting to reader so they will learn

  5. For next week • Identify a topic • Withone sentence for each, tell me: • What is your topic? • Why is it important for vision? • Why is it interesting? • Based on this I will suggest some references

  6. Wiki project timeline • Description of each week’s wiki project assignment is on the web • 4/11 - Identify topic • 4/18 - Make intro page and find references • 4/25 – 1st main page • 5/11 - Final project finished

  7. Wiki project ideas • In depth study of an animal visual system (mantis shrimp, humans, comparison of primates) • Tetrachromatic females • Instrumentation used by optometrist to check your vision • Characteristics of light environment • Color and polarization in the sky

  8. More ideas • Flicker fusion frequency - temporal perception • Depth perception • Fluorescence in the ocean • Animal coloration and camouflage • Eye research of UMd faculty • Bill Jeffery, Betsy Quinlan, Dan Butts, Hey-Kyoung Lee, Richard Payne (not KLC) • Robotic vision

  9. Some topics done previously

  10. Todays topics • Why the retina is susceptible to disease • Major retinal diseases • Diabetic retinopathy • Age related macular degeneration • Other genetic diseases

  11. Structure of the retina Pigment epithelium Photoreceptors Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer

  12. Retina formation • Cells form once early in development • Prior to birth • In mammals, if cells are damaged, they do not regenerate • Lost forever • This is not true of fish where retina grows their entire life

  13. Retina under high stress #1 • High metabolism of photoreceptors • In dark, ion channels are open and current is constantly flowing • In the dark, normal state of synapse is to release glutamate Glutamate release

  14. Retina under high stress #2 High energy needs are met by the choroid (blood circulation behind RPE) and retinal vasculature (above ganglion cell layer)

  15. Retinal vasculature has hole around fovea Few blood vessels above retina but none above macula Most energy demanding tissue in nervous system has to get O2and energy in and waste out by diffusion

  16. Retina under stress #3 • Photoreceptors are exposed to high light levels • This includes damaging UV • Light sensitivity is reason for their existence • Still susceptible to light damage

  17. Structure of the retina

  18. Photoreceptors mRNA goes from nucleus (n) to inner segment (m, e) where protein is made and sent to outer segment (o) Rat rod Frog rods Green Red

  19. New membrane (proteins) added at boundary of inner and outer segments

  20. New outer segments are built up at same time

  21. Retina does turn over outer segments (OS) • Label photoreceptors with H3-methionine • Used to make proteins : follow these after they are added to OS • Outer segment turns over in 10 days (rat) 2 days 3 days 4 days Young 1967 7 days 9 days

  22. Tip of outer segment is removed by phagocytosis into RPE RPE Outer segment

  23. Phagosomes are present in rods and cones each day Rod shedding Cone shedding Rods shed at beginning of day Cones shed at beginning of night Young 1978

  24. Retinal disease • How is retinal health / disease diagnosed? • Examine fundus • Psychophysical testing • Electrophysiology

  25. Diagnosis #1 • Fundus imaging • Ophthalmoscope • Invented by Helmholtz

  26. Ophthalmascope • Illuminate the eye nearly on axis • View retina on axis

  27. Two vascular systems for retina Choroid is behind RPE - hidden from view Retinal vasculature - this is what see in fundus - no blood vessels on top of fovea / macula

  28. #2 Fluoroscein angiography • Inject fluorescent dye • Provides finer resolution of retinal vasculature • Look for fluid loss through capillaries

  29. #3 Higher resolution imaging : OCT • Optical coherence tomography • Essentially ultrasound with light • Get microscope like resolution of the retina Optical - uses light Coherence - interference from retinal layers compared to mirror Tomography - profile in sections

  30. Invention and development of OCT

  31. Optical coherence tomography

  32. OCT normal 3D view

  33. Blood build up on /in retina

  34. Age related macular degeneration Pigment epithelial detachment and drusen or deposits

  35. #4 Psychophysics • Behavioral response to stimulus • Visual acuity • Intensity • Temporal response • Peripheral vision • Color vision • Dark adapted (rod) vision

  36. #5 Electrophysiology • Record electrical response of the eye • Apply electrode (as a contact lens) • Measure potential in response to light pulse • Electroretinogram

  37. Electrical set up

  38. Neurons of retina Photoreceptors Horizontal cells Bipolar cells Amacrine cells Ganglion cells

  39. Normal ERG in response to flash of light

  40. Irregular ERG responses as a result of retinal disease

  41. Types of retinal disease • Most common (few % of population) • Glaucoma - next class • Diabetic retinopathy • Age related macular degeneration • All three have both genetic and non-genetic causes

  42. Health related information at National Eye Institute Info on many diseases

  43. Diabetic retinopathy • Diabetic eye disease • Damage to retina as result of having diabetes • Diabetic retinopathy • Damage to blood vessels of retina • May swell (aneurisms) and eventually block blood flow • As some are blocked, new vessels try to grow on surface of retina • Leading cause of blindness in adults

  44. Vision with proliferative retinopathy Blood leaks from vessels growing on surface of retina

  45. Prevention • Get eye exam • 40-50% of people with diabetes have some form of retinopathy • Keep blood sugar and blood pressure in check

  46. Treatment • Retinopathy can be treated with laser surgery • Use laser to shrink and seal leaking blood vessels • May also need vitrectomy - remove blood stained vitreous • 95% chance can prevent blindness over 5 yrs

  47. Age related macular degeneration (AMD) • Disease associated with aging of the eye • Destroys sharp central vision • Leading loss of vision in people > 60 yrs • Affects >1.7 M people

  48. Two kinds of AMD • Wet AMD • Blood vessels grow under retina and lift macula • May leak fluid which raises macula up from back of eye • Lose contact with RPE and blood supply • Rapid loss of vision • Symptom • Straight lines appear wavy

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