The document provides information on the anatomy, histology, functions, and physiology of the cornea. It discusses the five layers of the cornea - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The stroma comprises around 90% of the corneal thickness and contains regularly arranged collagen fibrils responsible for the cornea's strength and shape. The endothelium acts as a pump to maintain stromal hydration and the cornea's transparency through mechanisms involving sodium-potassium ATPase and carbonic anhydrase. The cornea's avascularity and regular structure allow it to function as the eye's main refracting surface and protect the internal structures of the eye

1. ARSLAN JAWAD
ROLL NO. 132, RAWALPINDI MEDICAL
COLLEGE
CORNEA

2. CORNEA
THE 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

3. CORNEA
 Anatomy
 Dimensions
 Topography
 Histology
 Blood Supply
 Nerve Supply
 Physiology
 Functions
 Transparency
 Hydration

4. 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

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

6. 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

7. MICROVILLI:
Superficial hexagonal cell folds
Stabilizes tear film
DENDRITIC CELL :
Langerhans cells
ID and representation for lymphocytes
Absent centrally

8. Bowman’s layer
NARROW, HOMOGENOUS
MODIFIED ZONE OF ANT. STROMA
ANT- BASEMENT MEMBRANE
POST- STROMA
BOUNDARY- JUNCT. B/W CORNEA AND
LIMBUS
ULTRASTRUCTURE
COLLAGEN FIBRILS - STRENGTH
POST- MORE PROGRESSIVE AND BLEND
INTO STROMA
CANNOT REGENERATE – COARSE SCAR.
NON-MYELINATED NERVES

9. 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

10. Descement’s Membrane
BASAL 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

11. Endothelium
MONOLAYER, HOMOGENEOUS, HEXAGONAL CELLS 5ΜM
MAINTAINS TRANSPARENCY BY
ENDOTHELIAL BARRIER FUNCTION
ENDOTHELIAL PUMP MECHANISM
EPITHELIAL BARRIER BETTER
BARRIER - CORNEA AND AQ. COMPARTMENT
PUMP MECH – ACTIVE NA-K-ATPASE
AQ. LEAK INTO STROMA FREED
YOUNG – 3000-5000 CELLS/MM²→2/3 IN ADULTS
↓500 CELLS/MM² - CORNEAL OEDEMA

12. Blood Supply
CORNEA IS AVASCULAR
ANT. CILIARY – 1 MM
SUB-CONJUCTIVAL

13. 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

14. 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

15. 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

16. 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

17. Stroma
90% OF CORNEA, UNIFORMLY ARRANGED COLLAGEN
FIBRILS
GROUND SUBS – GLYCOSAMINOGLYCANS
KERATAN SULFATE
DERMATAN SULFATE
CHONDROITIN
STROMA – WATER (70%), KERATOCYTES(5%)
ROLE – STRENGTH AND SHAPE
STROMA+ENDO = PRESERVE TRANSPARENCY
STROMAL OEDEMA – EPI/ ENDO MALFUNCTION
A.P. SPATIAL SEPARATION OF GROUND SUBS

18. 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
REPULSION
SP (EXCISED) – 50MMHG,
GAG IMBIBITION OF FLUID BY NEG. PRESSURE – IP
EXCISED – SP=IP ; NORMALLY IP↓ THAN SP DUE TO IOP
THUS, IP= IOP – SP ( 17 – 50 = AVEG. 30-40 )

19. GAG – RESIST’S FLOW ACROSS
RESISTANCE ↓ IF HYDRATION↑ - OEDEMA↑
NO LATERAL FLOW EXCEPT AT LIMBUS

20. 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.

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

22. 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.

23. Thank You