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ARSLAN JAWAD ROLL NO. 132, RAWALPINDI MEDICAL COLLEGE CORNEA

Cornea Basic

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Page 1: Cornea Basic

ARSLAN JAWADROLL NO. 132, RAWALPINDI MEDICAL COLLEGE

CORNEA

Page 2: Cornea Basic

CORNEATHE CORNEA IS A TRANSPARENT, AVASCULAR, WATCH-GLASS (OUTER - CONVEX AND INNER – CONCAVE) SMOOTH STRUCTURE WHICH FORMS THE OUTER 1/6TH OF EYE BALL.COVERS: IRIS, PUPIL AND THE ANTERIOR CHAMBER

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CORNEA

Anatomy Dimensions Topography Histology Blood Supply Nerve Supply

Physiology Functions Transparency Hydration

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Histology BEHIND THE PRE-CORNEAL TEAR FILM THE CORNEA SHOWS 5 TISSUE LAYER’S NAMELY,

epithelium Bowmans layer (ant. Limiting lamina) Stroma (substantia propria) Decements layer (post. Limiting lamina) endothelium

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Corneal Epithelium STRATIFIED, SQUAMOUS AND NON-KERATANIZED NUCLEATED CELLS OF 5-6 LAYERSBASAL CELLS: DEEPEST, PALISADE ON THE BASAL LAMINA, GERMINATIVE LAYERCOLUMNAR WITH FLAT BASE, ROUND HEAD AND OVAL NUCLEI ORIENTED PARALLEL TO THE LONG AXISWINGED/ UMBRELLA CELL’S: POLYHEDRAL CELLS CONVEX ANT. CAP CONVERGING BASE POST. PROCESS B/W THE BASAL CELL NUCLEI PARALLEL TO CORNEAL SURFACENEXT 2-3 LAYERS ARE POLYHEDRAL CELLS WHOSE BASE KEEPS INC. TOWARDS THE SURFACESURFACE CELLS – LARGEST IN AREA, NON-KERATANIZED AND NUCLEATED

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DESMOSOMES :

adhesion

Abundant – basal

Scarce - wing and surface

Zonulae occludents + desmosomes impermeable to all

but,

semipermeable in bathing pre-corneal tear film

Hemi-desmosomes – basal cell to basal lamina

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MICROVILLI:Superficial hexagonal cell folds Stabilizes tear film

DENDRITIC CELL :Langerhans cellsID and representation for lymphocytesAbsent centrally

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Bowman’s layer NARROW, HOMOGENOUS MODIFIED ZONE OF ANT. STROMAANT- BASEMENT MEMBRANEPOST- STROMABOUNDARY- JUNCT. B/W CORNEA AND LIMBUS

ULTRASTRUCTURE COLLAGEN FIBRILS - STRENGTHPOST- MORE PROGRESSIVE AND BLEND INTO STROMACANNOT REGENERATE – COARSE SCAR.NON-MYELINATED NERVES

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Stroma REGULARLY ARRANGED COLLAGEN BUNDLE LAMELLAE

CENTRAL (200-300)

PERIPHERAL (500)

PROTEOGLYCAN GROUND AND KERATOCYTES

LAMELLAE – PARALLEL, LIMBUS TO LIMBUS

ANT. ⅓ - OBLIQUE, RUNS INTO BOWMAN'S

DEEP STROMAL – STRAP LIKE

RIGHT ANGLES, AT PERIPHERY RUNS INTO

SCLERA AND RECTUS MUSCLE

LIMBUS – CIRCULAR COURSE

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Descement’s MembraneBASAL LAMINA OF ENDOTHELIUM

SYN. ALL LIFE, FROM 2ND GEST.

BIRTH – 3-4ΜM

CHILDHOOD - 5ΜM

ADULT – 10-12ΜM

SHARPLY DEFINED STRONG RESISTANT SHEET

THICKENS – AGE AND DEGEN CONTD.

MAJOR PROTEIN – TYPE IV COLLAGEN

GLYCOPROTEINS +PROTEOGLYCANS = PINK ON ACID SCHIFF

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Endothelium MONOLAYER, HOMOGENEOUS, HEXAGONAL CELLS 5ΜMMAINTAINS TRANSPARENCY BY ENDOTHELIAL BARRIER FUNCTION

ENDOTHELIAL PUMP MECHANISMEPITHELIAL BARRIER BETTERBARRIER - CORNEA AND AQ. COMPARTMENTPUMP MECH – ACTIVE NA-K-ATPASE AQ. LEAK INTO STROMA FREED

YOUNG – 3000-5000 CELLS/MM²→2/3 IN ADULTS ↓500 CELLS/MM² - CORNEAL OEDEMA

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Blood Supply

CORNEA IS AVASCULAR ANT. CILIARY – 1 MMSUB-CONJUCTIVAL

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Functions of Cornea

Functions of cornea are :

1. Refraction of light

2. Transparency

3. Containing of intra-ocular pressure

4. Protection (corneal reflex)

The collagen fibrils matrix found in the stromal layer is

responsible for the containing IOP

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Transparency TRANSPARENCY IS DUE TO

›Anatomical

›Avascularity

›Epithelial non-keratinization

›Stromal lamellar packing

›Non-myelinated nerves

›Pre-corneal tear film

›Physiological

›Corneal dehydration

›Uniform refractive index

WATER FROM ENDOTHELIUM MAINTAINS OPTICAL HOMOGENEITY

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MAURICE THEORY: EXPLAINED ON THE BASIS OF STROMAL LATTICE ARRANGEMENT OF COLLAGEN FIBRILS SMALL DIAMETER – REGULAR SPACING – LIGHT BACK SCATTER SUPPRESSED – DESTRUCTIVE INTERFACE

GOLDMAN THEORY: FIBRIL SEPARATION AND A DIAMETER ↓ ⅓ OF THE WAVE LENGTH OF INCIDENT LIGHT – PERFECT TRANSPARENCY

LOSS OF TRANSPARENCY - CORNEAL SCARING – NEW COLLAGEN – IRREGULAR INTERWEAVING

STROMAL – CORNEAL OEDEMA - ↑ SPACES – FLUID LAKES – STROMAL CLOUD → IRREGULAR SURFACE VIZ IRREGULAR ASTIGMATISUM EPITHELIAL OEDEMA: ILL FIT CL/ IOP → SEPERATION OF BASAL CELLS BY OEDEMA → DIFFRACTION GRATING EFFECT IMP. SYMP IN SUB AC. ANGLE CLOSURE GLAUCOMA

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MAIN FUNCTION→ OPTICS FORMS PRINCIPLE REFRACTING SURFACE ( 70% ) FACTORS SUCH AS -

Transparency Smooth anterior surface Uniform arrangement of epithelial cells Closely packed stromal lamellae of uniform size Avascularity

Help in maintaining a clear cornea Factors that effect cornel hydration viz transparency corneal epithelium corneal stroma corneal endothelium

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Stroma 90% OF CORNEA, UNIFORMLY ARRANGED COLLAGEN FIBRILS GROUND SUBS – GLYCOSAMINOGLYCANS

KERATAN SULFATEDERMATAN SULFATECHONDROITIN

STROMA – WATER (70%), KERATOCYTES(5%)ROLE – STRENGTH AND SHAPESTROMA+ENDO = PRESERVE TRANSPARENCYSTROMAL OEDEMA – EPI/ ENDO MALFUNCTION A.P. SPATIAL SEPARATION OF GROUND SUBS CORNEAL DIAMETER DOESN'T SWELL

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Stromal Swelling Pressure STROMA – EXCISED (78%) HYDRATED

AQ. MEDIUM (98%) HYDRATED GLYCOSAMINOGLYCAN'S – MAJOR CAUSE OF HYDRATION KERATAN SULFATE AND CHONDROITIN – ELECTROSTATIC REPULSION – SWELLING COLLAGEN FIBRILS – CROSS-LINK– EXPAND WITH REPULSIONSP (EXCISED) – 50MMHG, GAG IMBIBITION OF FLUID BY NEG. PRESSURE – IPEXCISED – SP=IP ; NORMALLY IP↓ THAN SP DUE TO IOPTHUS, IP= IOP – SP ( 17 – 50 = AVEG. 30-40 )

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GAG – RESIST’S FLOW ACROSS RESISTANCE ↓ IF HYDRATION↑ - OEDEMA↑

NO LATERAL FLOW EXCEPT AT LIMBUS

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Pump Mechanism ENDOTHELIUM – IMP. PUMP MECH (ACTIVE PROCESS)

NA/K-ATPASE – QUBAIN ATP INHIBITOR – BLOCK ENDO. FLUID TRANSPORT – OVER HYDRATION BICARBONATE – THGH NEG ELECTRICAL POTENTIAL – THIOCYANATE CARBONIC ANHYDRASE – CARBONIC ANHYDRASE INHIBITORS – STROMA TO AQ.

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Evaporation

EVAPORATION OF WATER → CON. AND INCREASE OSMOLARITY HYPERTONICITY OF TEARS DRAW THE WATER FROM CORNEA READILY REPLACED BY AQUEOUS AVEG LOSS – 4%

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Intra-ocular Pressure DOESN'T CAUSE EPI. OEDEMA, NOT ASSOCIATED WITH

CORNEAL THICKNESS

BUT, WHEN IP IS +VE I.E

IOP ↑ - SP = EPITHELIAL OEDEMA

EG: ↑IOP AND SP NORMAL = EPI. THICKENING – GLAUCOMA

NORMAL IP AND ↓ SP = ENDO. DYSTROPHY.

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Thank You