cornea basic
TRANSCRIPT
ARSLAN JAWADROLL NO. 132, RAWALPINDI MEDICAL COLLEGE
CORNEA
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
CORNEA
Anatomy Dimensions Topography Histology Blood Supply Nerve Supply
Physiology Functions Transparency Hydration
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
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
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
MICROVILLI:Superficial hexagonal cell folds Stabilizes tear film
DENDRITIC CELL :Langerhans cellsID and representation for lymphocytesAbsent centrally
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
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
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
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
Blood Supply
CORNEA IS AVASCULAR ANT. CILIARY – 1 MMSUB-CONJUCTIVAL
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
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
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
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
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
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 )
GAG – RESIST’S FLOW ACROSS RESISTANCE ↓ IF HYDRATION↑ - OEDEMA↑
NO LATERAL FLOW EXCEPT AT LIMBUS
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.
Evaporation
EVAPORATION OF WATER → CON. AND INCREASE OSMOLARITY HYPERTONICITY OF TEARS DRAW THE WATER FROM CORNEA READILY REPLACED BY AQUEOUS AVEG LOSS – 4%
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.
Thank You