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

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Presentation on theme: "Lecture #19 Eye diseases of cornea, lens and vitreous 4/9/13."— Presentation transcript:

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 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 part Tears 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 1.Epithelium 10% of thickness Blocks foreign matter Absorbs O 2 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 stroma doesn’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 Situ Keratomileusis 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

46 Lens Transparent so light is efficiently transmitted High index so light is focused onto the retina

47

48 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

49 Crystallins α-crystallins Related to heat shock proteins β and γ crystallins γ crystallins are symmetric

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

51 Recruitment of proteins Recruited to lens by changing gene expression May be result of gene duplication followed by new expression Proteins selected which highly stable Contribute to index of refraction Insensitive to UV damage

52 Crystallin structure Crystallins are present from birth Processes which damage protein are bad Oxidation, deamidation, cleavage Result in protein unfolding Normally α crystallins are chaperones keeping other proteins folded As lens proteins unfold, α crystallins used up Unfolded proteins form precipitates Loss of lens transparency

53 Cataracts Clouding of lens Typically occurs with age 50% of people > 80 have cataracts Cataracts affect 5.5 million people in US

54 Cateract symptoms Blurry vision Poor night vision Problems with glare

55 Cataracts Congenital Age related

56 Age related cataract prevention Decrease sun exposure Increase antioxidants Stop smoking Get eye exam

57 Treatment #1 Cut small incision (3 mm) Remove front of lens to expose cataract Use ultrasound to fragment cataract Remove fragments

58 Treatment #2 Replacement lens Made of plastic Blocks UV Is flexible so can attach to eye focusing muscles Focus near and far!

59 Treatment #2 Introduce replacement lens into lens capsule May only replace part of lens Can improve spectral transmission (more blue)

60 Glaucoma

61

62 Variety of diseases that result in loss of retinal ganglion cells Loss begins in periphery 50% of people have glaucoma and don’t realize it

63 Fluid flow at front of eye Aqueous humor is generated by ciliary body and flows into anterior chamber to nourish eye Flows out where cornea and iris meet Iridocorneal angle Trabecular and uveoscleral drainage Spongy tissues

64 Fluid flow at front of eye If fluid does not drain: Pressure in eye builds up This damages retinal ganglion cells and vision is lost

65 Measuring eye pressure Applanation tonometry Measure applied pressure necessary to deflect cornea Noncontact tonometry Measure air pressure needed to deflect cornea

66 Caveats High intraoccular pressure (IOP) is highest risk factor but: Majority of people with high IOP do not get glaucoma Optic nerve damage can occur even without high pressure -Low tension or normal tension glaucoma

67 Risk factors Affects 70 million people Age 2 % over age 40; 7% over age 80 Over age 40 - African Americans 5x more likely Over age 60 - Mexican Americans more likely Family history of glaucoma Though not Mendelian trait

68 Symptoms Gradual loss of peripheral vision Can be slow loss over years No pain Difficult to notice effects

69 Kinds of glaucoma Open angle glaucoma Fluid seems to keep flowing Developmental glaucoma Anterior portion of eye doesn’t develop correctly Pigmentary glaucoma Iris pigment epithelium atrophies and pigment clogs drainage of fluid

70 Open angle glaucoma

71 Genetics 9 loci identified so far that initiate primary open angle glaucoma Explain only small % of cases Two genes which cause early onset glaucoma Myocilin (3% of cases) Optineurin Not obvious how genes cause the disease Expressed in both retinal ganglion cells and trabecular meshwork May cause problems if protein misfolding

72 Treatments Eye drops or pills Decrease fluid production or increase drainage Laser trabeculoplasty Laser widens holes in drainage meshwork Conventional surgery Create new exit pathways

73 Open fluid flow in meshwork or sclera

74 Use of marijuana to treat glaucoma

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77 Next time Gene therapy How do you replace a faulty gene?


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