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Lecture # 19

Lecture # 19

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Lecture # 19

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  1. Lecture #19 Eye diseases of cornea, lens and vitreous 4/9/13

  2. Animal wikis • Great! • Some of my favorites • Writing: manatees, hummingbirds • Link to eye design: barn owls, panda

  3. Wiki homework • Be thinking about your wiki final project topic • Email it to me by end of Thursday • It is fine if your topic evolves as you gather information • May want to focus it down if find lots info • May need to expand if not so much

  4. Anterior eye disease • Cornea • Dystrophies • Refractive errors • Lens • Cataracts • Vitreous • Glaucoma

  5. Function of cornea • Performs ≈70% of focusing • Protects eye from outside world • No blood supply • Cleaned and nourished by tears and aqueous humour

  6. Corneal disease • Conjunctiva • Mucous membrane lining eyelid and sclera • Contains tiny blood vessels • Pink eye - conjunctivitis • Infection by either bacteria or virus • Corneal infections • Bacterial or fungal invasion into corneal layers

  7. Dry eye

  8. Tears • Basal tears • Constantly produced to nourish and moisten eye • Mixture of aqueous and oily secretions • Reflex tears • Made in response to irritation or emotion • More watery

  9. What are tears? • Tears are made of three layers • Oily, lipid layer - keeps aqueous layer from evaporating • Aqueous layer - keeps eye moist • Mucin layer - helps aqueous layer spread

  10. Meibomian gland produces lipid part

  11. Lacrimal glands produce aqueous partTears drain to naso-lacrimal sac

  12. Goblet cells produce mucus

  13. Tears then need to drain Tears then drain out through holes in eyelid If drain too quickly, eyes become dry Plug these holes

  14. Dry eye • If meibomian glands get blocked, there will not be enough lipids and tears will evaporate too quickly • To unclog glands • Heat treatments • Doxycycline • Nutritional supplements • May be other reasons not enough lipids

  15. Dry eye • If there is not enough aqueous part of tears • Use artificial tears • Plug up drainage holes so stay on eye longer • May also be problems with mucin layer which wets the eye and helps aqueous layer to spread • Not sure how to improve it

  16. Cornea has 5 layers • Epithelium 10% of thickness • Blocks foreign matter • Absorbs O2 and nutrients from tears • Epithelia cells grow and are anchored to basement membrane • Many tiny neurons - very sensitive to pain

  17. Cornea has 5 layers 2. Bowman’s layer Strong layer of fibers composed of collagen If injured it forms scar tissue

  18. Cornea has 5 layers 3. Stroma Comprises 90% of cornea thickness Composed mostly of collagen (16%) and water (78%) Gives cornea shape and transparency Upper part of stroma repairs itself but lower part does not

  19. Cornea has 5 layers 4. Descemet’s membrane Thin but strong protective layer Made of collagen (different from stroma) Made by endothelium Can regenerate after injury Descemet’s membrane

  20. Cornea has 5 layers 5. Endothelium Extremely thin Fluid slowly leaks from inside eye into stroma Endothelium pumps it back out so stromadoesn’t get cloudy!! Endothelium does not regenerate - if damaged, need corneal transplant

  21. Corneal dystrophies • Over 20 kinds • Dystrophy - abnormal development • Inherited • Affect both eyes equally • Begin in one of 5 layers and spread to others • Layers become cloudy - so can’t see

  22. Keratoconus • Thinning of middle of cornea (stroma) causes cornea to change shape • - cone like • Most common corneal dystrophy • Affects 1:2000 • Inherited or from wearing hard contacts or eye injury • Usually stabilizes and correct with glasses / contacts

  23. Lattice dystrophy • Build up of amyloid (protein) deposits in upper to middle stroma • Create a lattice which worsens and makes cornea cloudy

  24. Fuchs dystrophy • Endothelial layer deteriorates • Can’t pump out aqueous humour so cornea swells • Vision becomes blurry

  25. Treatments for corneal dystrophies • Corneal transplants • Match by blood type • 20% rejection rate

  26. Treatment for corneal scars • Phototherapeutic keratectemy • Laser ablation • Remove scarred or damaged tissue • Use UV excimer laser under computer control

  27. Refractive error • If cornea has wrong curvature, image on retina is out of focus • Myopia - image focused in front of retina : 25% of people • Hyperopia - image focused behind retina

  28. Refractive error • Astigmatism • Cornea is more curved in one direction than the other (like spoon or football) Multiple focal lengths so multiple images Always blurry

  29. Treatments for refractive errors - reshaping the cornea • RK - Radial keratotomy • PTK - Phototherapeutic keratectemy • LASEK -Laser assisted sub-epithelial keritectomy • LASIK - Laser Assisted In Situ Keratomileusis

  30. Radial keratotomy • Modify cornea shape by cutting slits • Developed in Russia in 1970s • Unpredictable healing • Vision may change through day or over time • Not recommended

  31. Treatment for refractive errors • Phototherapeutic keratectomy • Can also be used to reshape cornea - correct myopia • Remove epithelial layer and reshape upper part of cornea • Epithelial layer regenerates Keratectomy - remove part of cornea

  32. LASEK surgery • Laser assisted sub-epithelial keratectomy • Cut and peel back epithelial layer • Re-shape upper stroma just below epithelium with laser • Replace epithelial layer

  33. LASIK refractive surgery • Laser Assisted In SituKeratomileusis • Cut a flap in cornea with blade or laser (this cuts more than just epithelium) • Laser vaporizes stroma to reshape it • Flap is folded back though doesn’t seal • Epi-LASIK cuts thinner flap so does reseal

  34. What happens during LASIK surgery

  35. Reshaping of cornea • Near sighted • Far sighted

  36. Comparisons suggest LASEK and LASIK produce equivalent results

  37. Some reasons NOT to do LASIK • You may not be suited for procedure: • Eye disease • Thin corneas • Unstable vision • Vision may get worse • Unstable cornea • No long term data • LASIK corneal flap may be deep in cornea • These tissues do not regenerate • Flap is permanent

  38. Possible complications - starbursts LASIKdisaster.com

  39. Possible complications - halos LASIKdisaster.com

  40. Ghosting

  41. Near sighted problems - PRK

  42. Far sighted problems

  43. Possible problems

  44. NEI - cataracts

  45. Lens • Lens • Transparent so light is efficiently transmitted • High index so light is focused onto the retina

  46. Lens composition • Composed of water and lens crystallins (90% of protein) • Crystallins made once and then stored in lens for rest of life • Must remain soluble to be transparent Eye lens fiber cells filled with crystallins

  47. Crystallins • α-crystallins • Related to heat shock proteins • β and γcrystallins γcrystallins are symmetric

  48. Other proteins can be co-opted to form part of lens Many are active metabolic enzymes elsewhere in body!!!