Minimalinvasiveglaucomasurgerylllll.pptx

Migs glaucoma surgery

1. INTRODUCTION Thick, tough, transparent avascular tissue Forms anterior 1/6 th of eyeball Smooth, convex surface and concave inner surface with uniform curvature Resemble small watch glass Twice as thick at periphery than at centre(0.5mm)

2. FUNCTION Main function is optical-forms principal refraction surface (70%) 40-45 dioptre of total refractive power (60d) Resistance provide protective layer Resist ocular pressure due to collagenous components of stroma

3. DIMENSION Surface Anterior Posterior Shape Elliptical Round H o rizontal diameter 11.7 mm 11.7 mm Vertical diameter 10.6 mm 11.7 mm Radius of curvature 7.8 mm 6.5 mm Surface area - 1.3cm2

4. C entral -0.52 mm P eripheral -0.67 mm At birth- cornea is slightly thicker than in children THICKNESS OF CORNEA

5. Applied anatomy Calculation of corneal thickness is important in IOP estimation Thicker cornea –falsely higher IOP reading and vice versa Central corneal ulcers are more prone to perforation than peripheral corneal ulcers. In follow up of corneal transplant patients to determine endothelial function & its recovery

6. METHODS OF MEASURING CORNEAL THICKNESS Ultrasonic pachymetry Optical pachymetry Optical coherence tomography (OCT) Laser inferometry High resolution ultrasonography

7. Ultrasonic pachymeter Optical pachymeter Laser inferometry OCT

8. Apica l zone ZONES OF CORNEA Central Zone-1-2mm Paracentral Zone- outer Diameter of 7-8mm Peripheral Zone Or Transitional Zone- 11mm Limbal Zone-12mm

9. REFRACTIVE PROPERTY OF CORNEA Refractive power Anterior surface : +48 D Posterior surface : -5 D Net refractive power: +43 D Central 5 mm area forms the powerful refractive surface Refractive index =1.37

10. HISTOLOGICAL STRUCTURE

11. HISTOLOGICAL STRUCTURES OF CORNEA

12. EPITHELIUM Stratified, squamous, non-keratinised epithelial cells 5-10% of total corneal thickness Continuous with conjunctiva at corneal limbus 50- 90 micrometer thick Consist of 5- 7 layers of nucleated cells

13. MOST SUPERFICIAL CELLS Flattened cells are two most superficial cell layers These cells are 45 mm long and 4mm thin with flattened nuclei. Zonulae occludentes are also found in this layer. Anterior cell wall of these cells has many microvillia play an important role tear film stability. Microvillia contain glycocalyx .

14. Ultra structural structure Mostly hexagonal Exhibit surface microvillae or microplicae – serves as physical function in stabilising deep precorneal tear fil m

15. WING CELLS 2-3 layers Polyhedral Wider &increasingly flattened towards surface Convex anteriorly

16. Ultrastuctural structure Possess numerous tonofibrils Moderately abundant mitochondria High glycogen content Attached with basal cells posteriorly and other wing cells laterally and anteriorly via tight junction

17. BASAL CELLS Deepest layer Continuous peripherally with that of limbus Columnar (width-10μm, tall- 15μm) Each nucleus is oval Oriented parallel to cell’s long axis

18. Ultrastructural structure : Mitochondria is less Connected to one another by desmosomes Underlying basal lamina by hemidesmosomes

19. BASAL LAMINA Secreted by basal cells Synthesize hemidesmosomal structures concerned in attachment of epithelium to lamina Type VII collagen Tight adherance of basal epithelium to subjacent cornea

20. CLINICAL SIGNIFICANCE OF BASAL LAMINA Abnormal basal lamina lead to recurrent erosions & epithelial defect Ageing & diabetes : thick & multilaminated Epithelial oedema- adherence between basal lamina & basal cells get less firm thus gets readily detached

21. EPITHELIAL CELL ADHESION Superficial flattened cells are attached to each other by zonula occludentes (tight junctions) Desmosomes Maculae occludentes Wing cells: desmosomes & large gap junctions Basal columnar cells: desmosomes Maculae occludentes Hemidesmosomes

22. APPLIED ANATOMY OF EPITHELIUM 1. Irregularity of corneal epithelium disrupts smoothness of cornea-air interface affecting visual acuity (eg: post LASIK surgery) 2. In vitamin A deficiency, corneal epithelium expresses keratins

23. 3. Epithelial defect loss of epithelium Superficial without inflammation- abrasion or erosion Deep with inflammation in surrounding cornea- ulcer Stained with fluorescein green

24. Epithelial odema - Impairs vision more than stromal oedema 5. Epithelial deposition of iron occurs in keratoconus forming fleischer ring

25. NONEPITHELIAL CELLS Wandering histiocytes Macrophages Lymphocytes Pigmented melanocytes

26. BOWMAN’S LAYER Modified region of corneal anterior stroma Narrow, acellular homogenous zone 8-14μm thick Immediately subjacent to basal lamina of cornea epithelium

27. once destroyed not renewed-replaced by coarse scar tissue Anterior surface-smooth and parallel to that of cornea Perimeter of bowman’s layer- rounded border- delineates anterior junction between cornea and limbus

28. ULTRASTRUCTURE: Meshwork of fine collagen fibrils (type V) Compacted arrangement of collagen

29. CLINICAL SIGNIFICANCE OF BOWMAN’S MEMBRANE Wounds & ulcers penetrating into bowman’s membrane New collagen fibres are produced in irregular pattern during healing Corneal opacity

30. CORNEAL OPACITY

31. TYPES N E B U L A R Scars involving superficial stroma along with bowman’s membrane MAC U L A R Scarring involves bowman’s membrane +1/2 of stroma LE U COM A T OUS Scarring involves bowman’s membrane +>1/2 of stroma

32. STROMA (SUBSTATIA PROPRIA) 500μm thick Comprises 90 % of corneal thickness Composed of Collagen fibrils/lamellae Cells embedded in hydrated matrix of proteoglycans (ground substance)

33. 1. LAMELLAE Regularly arranged Many layered : 200-300 centrally 500 peripherally Each lamellae arranged in parallel with each other and with corneal surfaces Most predominant type I collagen

34. Becomes continuous with scleral lamellae at the limbus Anterior 1/3 rd stroma: oblique orientation Posterior 2/3 rd stroma: alternating layer of lamellae at right angle to each other

35. Applied anatomy-influence different effect of cornea or limbal incision during cataract surgery on postoperative corneal shape

36. LAMELLAE ARRANGEMENT

37. 2.5-5% volume Long, thin and flat cell with eccentric nucleus parallel to corneal surface Produces ground substances and collagen during embryogenesis and after injury 2 . KERATOCYTES

38. 2 . Wandering cells Migrate from marginal loops of corneal blood vessels to site of injury Histiocytes Lymphocytes Dendritic ( langerhan’s cells ) present in fetal corneal stroma disappear in mature cornea except in periphery

39. CLINICAL SIGNIFICANCE Corneal transparency due to regularity & fineness of collagen fibrils and the closeness & homogeneity of their packing Parallel arrangement of fibrils makes dissection easy during superficial or lamellar keratoplasty Weave pattern at periphery Gives strength to peripheral cornea Maintains corneal curvature

40. 4. Lipid deposition in stroma with ageing - arcus senilis 5 . Hypercholestemia - arcus juvenilis

41. 4. DUA’S LAYER 15 μm thick layer Located between the corneal stroma and descemet’s M embrane Incredibly tough and strong Mostly composed of type 1 collagen

42. Type 4,5,6 also present Proteoglycans- lumican, mimecan, decorin CD34 negative Does not extend to periphery

43. Scientists now believe that corneal hydrops, a bulging of cornea caused by fluid build up that occurs in patients with keratoconus ,is caused by a tear in dua layer, through which water from inside eye rushes in and causes waterlogging ( Harminder s. Dua , lana A. Faraj , dalia G. Said , trevor gray , james lowe .Human corneal anatomy redefined.: A novel pre- descemet's layer (dua's layer).The academic journal ophthalmology,2013)

44. DESCEMET’S MEMBRANE Basal lamina of corneal endothelium First appear at 2 nd mth of gestation Synthesis continue throughout adult life Laminated structure Physical characteristics- elasticity regenerate

45. Strong resistant sheet –closely applied to back of corneal stroma, unlike basal lamina, sharply defined and plane of separation use at lamellar keratoplasty Type IV collagen, glycoprotein and proteoglycan

46. CLINICAL SIGNFICANCE OF DESCEMET’S MEMBRANCE May remain intact even in severe corneal ulceration and maintain the integrity of the eyeball even when the whole stroma is sloughed off by descemetocele. Descemet folds are seen in corneal oedema.

47. HAAB’S STRIAE Healed breaks in descemet’s membrane Descemet’s tears are seen in congenital glaucoma

48. Fuch’s dystrophy Accelerated endothelial cell loss abnormal endothelial cell secretes – excrescences on DM called guttattae-presence of irregular warts (increased endothelial permeability)

49. 5. Thickens with age & in degenerative conditions Congenital endothelial dystrophy Posterior polymorphous dystrophy 6. Altered descemet only in posterior 2/3 rd signifies disease process has occurred after birth

50. 7. Schwalbe’s line internal landmark of corneal limbus anterior limit of trabecular meshwork 8. Copper deposition in descemet membrane Wilson’s disease- K-F ring

51. 6. ENDOTHELIUM Single layer Contains hexagonal cuboidal cells Cell density of endothelium: At birth: 6000 cells/mm2 Count decreases by 26% by age 1 yr Further decrease by 26% by age 11 yrs

52. Rate of loss slows and stabilises around middle age Adults : 2400 (1500-3000 ) Cell number decreases with age because there is no mitosis

53. Attached to descemets membrane by hemidesmosomes and laterally to each other by tight junctional complexes Responsible for maintaining the water balance of stroma

54. APPLIED ANATOMY If endothelial pump is dysfunctional, it will result in corneal edema Minimal endothelial cell count for maintainence of normal corneal function=1000 Corneal decompensation occurs if 75% are lost i.E cell count <500cells/mm2

55. CLINICAL SIGNIFICANCE OF ENDOTHELIUM: Surgeries affect endothelial cell count (cell loss around 8-10%) Eg: cataract surgery( min count 1000-1500), graft of PK( min count-2000) In keratoconus or dm patients, endothelial morphology changes without a decrease in cell density.

56. Corneas with low cell density do not tolerate intraocular surgery Accelerated cell loss seen in fuch’s endothelial dystrophy CHED focal or generalised loss of endothelium

57. EVALUATION OF ENDOTHELIAL LAYER Endothelial cell layer can be examined with slit lamp by specular reflection & retroillumination Specular microscope gives detail picture along with the cell count

58. BLOOD SUPPLY AND LYMPHATIC DRAINAGE Cornea avascular Devoid of lymphatic drainage Anterior ciliary arteries (of conjunctiva and sclera) Capillary blood vessels Nourised by diffusion from aqueous humour From capillaries at its edges

59. Central part Oxygen indirectly from air via o2 dissolved in tear film Peripheral part Oxygen by diffusion from anterior ciliary blood vessels

60. Corneal neovascularization: sprouting of perilimbal vessels Cornea is immunoprivileged site with respect to graft rejection Delayed wound healing after corneal ulcer, laceration& keratoplasty

61. NERVE SUPPLY

62. NERVE SUPPLY OF CORNEA Trigeminal nerve Opthalmic division Nasociliary nerve Long ciliary nerves Enter eyeball around optic nerve with short ciliary nerve Run forward in the suprachoroidal space

63. A short distance from limbus, pierce the sclera to leave the eyeball Divide dichotomously and connect with each other and conjunctival nerves Pericorneal plexus : 60-80 trunks(myelinated) Enters the cornea at various levels-sclera, episclera and conjunctiva

64. After going 1-2mm in the stroma, myelin sheath is lost and branch dichotomously and form stromal plexus Some end in mid-stroma and some pass anteriorly and forms sub-epithelial plexus Fibres from subepithelial plexus penetrate pores in bowman’s membrane - lose their schwann’s sheath - divide into filaments under basal layer of epithelium

65. Filaments extends between layers of epithelial cells and form intraepithelial plexus Ends as fine beaded filaments

66. CLINICAL SIGNIFICANCE Cornea is highly innervated - corneal erosions & ulcer are highly painful. Loss of corneal sensation can predispose to neurotrophic ulcers as in leprosy, diabetes. Perineuritis seen in acanthamoeba keratitis

67. REFERENCES WOLFF’S A N A T O M Y C L INICAL A N A T O M Y O F E Y E ( S N E L L ’ S ) PRINCIPLES AND PRACTICE OF OPHTHALMOLOGY PARSON’S DISEASES OF THE EYE (19 TH EDITION) AAO SECTION 8 (EXTERNAL DISEASE AND CORNEA) 2016-2017 JACK J KANSKI 8 TH EDITION

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