The cornea develops from surface ectoderm, mesenchyme, and neural crest cells during embryogenesis. It has five layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The stroma comprises the majority of the cornea and contains tightly packed collagen fibrils for strength. The endothelium regulates hydration to maintain corneal transparency. Metabolic processes and the avascular nature of the cornea allow it to remain clear by preventing edema. The cornea refracts light, protects the eye, and contains nerves for sensation.
5. ANATOMY
Optical zone:
-Cornea is almost a sphere, the central 1/3rd is called
optical zone about 5.4 mm
Radius of curvature:
-Anterior surface – about 7.8 mm
-Post. Surface – about 6.5 mm
Refractive power: +43.1 D
(Air-tear = +43.6 D, Tear-cornea = +5.3 D, Cornea-
aqueous = -5.8 D)
Refractive index: 1.376
9. ANTERIOR CORNEAL EPITHELIUM
The corneal epithelium is -
-Stratified, squamous and non-
keratinized
-Continuous with conjuctival
epithelium at limbus but having
no goblet cells
-50-90 μm in thickness
-Consists of 5 or 6 layers of
nucleated cells resting on a basal
lamina, namely-
a. Basal cells
b. Wing cells
c. Surface cells
10.
11. ANTERIOR CORNEAL EPITHELIUM
• Basal cells:
• -Deepest cell layer
• -Stand in a palisade manner on basal lamina
• -Germinative layer of the epithelium
• -Columner with rounded heads and flat bases
• -Nucleus is oval and oriented parallel to the
cells long axis
12. ANTERIOR CORNEAL EPITHELIUM
• Wing or umbrella cells:
• -Second epithelial cell layer (1-2 layers of cells)
• -Polyhedral cells
• -Convex anteriorly forming cap over basal cells
and send processes between them
• -Nucleus is oval and oriented parallel to
corneal surface
13. ANTERIOR CORNEAL EPITHELIUM
• Surface cells:
• -Most superficial 2-3 layers of cells
• -Also polyhedral and become wider & flattened
towards the surface
• -Flattened nuclei project backwards leaving the
surface perfectly smooth
• -Most superficial cells are mostly hexagonal in
shape and exhibit surface microvilli or
microplicae
14.
15. ANTERIOR CORNEAL EPITHELIUM
• Basal lamina:
• -The basal lamina is secreted by the basal cells
• -0.5 - 1 μm wide
• -Ultrastructurally it is distinguished in to two
patrs –
• i. Lamina lucida (superficial)
• ii. Lamina densa (deep osmiophilc)
16.
17. BOWMAN’S MEMBRANE
• -Modified region of anterior stroma
• -Acellular homogeneous zone
• -8 – 14 μm thick
• -Ant. surface is smooth & parallel with corneal
surface
• -It delineates the anterior junction between
cornea and limbus
18. BOWMAN’S MEMBRANE
• It is perforated many places by nerve to
epithelium
• Compact arrangement of collagen gives it
great strength and relatively resistant to
trauma both mechanical and infective
20. CORNEAL STROMA
• -About 500 μm thick (about 90% of corneal
thickness)
• -Consists of regularly arranged lamellae of
collagen bundles, lie in proteoglycan ground
substance with –
• -200 – 300 bundles – centrally
• -500 bundles – peripherally
• -Width about 9 – 260 μm
• -Height about 1.15 – 2 μm
• -Small population of cells – keratocytes present
21. CORNEAL STROMA
• -Arrangement of lamellae –
• -Lamellae are arranged in layers, parallel with
each other & with corneal surface
• -In deeper stroma the lamellae form strap-like
ribbons which run approximately at right angles
to those in consecutive layers
• -At the periphery this right-angular arrangement
is slightly changed where it gets scleral fibres
• -At the limbus the bundles appeared to take a
circular course
22. CORNEAL STROMA
• -Each lamellae comprises of a band of collgen
fibrils arranged in parallel with each other
• -Fibrils show typical 64 nm periodicity of
connective tissue collgens with a microperiod
of 6 nm
• -There is a unique uniformity of fibril
diameter, it is 22 (±1) nm from ant. to post.
• -There is remarkable regularity of seperation
both within and between lamellae
23. CORNEAL STROMA
• -The keratocytes occupy 2.5 – 5 % of total stromal volume
and is responsible for synthesis and maintaining of collagen
& proteoglycan substance of stoma
• -Keratocytes:
• -Long, thin, flattened cells (maximally 2μm thick) running
parallel to corneal surface
• -Having long flattened nuclei, sparse cytoplasm but
contains full component of organells
• -Position – between the lamellae
• -There stellate processes extened for great distance and
frequent contacts are made with other keratocytes in same
horizontal plane forming gap junctions
• -Lymphocytes, macrophages and polymorphonuclear
leucocytes (very rarely) also found in stroma ocationally
24. DESCEMET’S MEMBRANE
• -It is the basal lamina of corneal endothelium
• -First appears at 2nd month of gestation and synthesis
continue throughout adult life
• Thickness – at birth :- 3 – 4 μm
• at childhood :- about 5 μm
• at adult :- 10 – 12 μm
• -There is a distinct structural difference between fetal &
postnatal components
• -It is a strong resistant sheet
• -It thickens with age and in some corneal degenerative
conditions
• -Major protein of DM is Type IV collagen
27. ENDOTHELIUM
-It is a single layer of hexagonal, cuboidal cells
attached posterior aspect of DM
-It is nuroectodermal in origin
-Corneal endothelial cells production is relatively
fixed, it is about 500000
28. ENDOTHELIUM
• about 6000 cells/mm² at birth
• 26% lost in 1st year
• Further 26% lost over next 11 years
• Rate of cell loss slows and stabilizes around
middle age and then it is about 2500 cells/mm
• Single oval nucleus located centrally
• Cells shape is hexagonal in youth with age it
become polymorphic
29. BLOOD SUPPLY
-Small loops derived from
the anterior ciliary
vessels invade its
periphery for about 1
mm.
-Actually, these loops are
not in cornea but in the
subconjunctival tissue
which overlaps the
cornea.
30. NERVE SUPPLY
• Cornea is rich in sensory nerve supply derived
from ophthalmic division of trigeminal nerve via
anterior ciliary nerves and nerves to the
surrounding conjunctiva –
• Ant.ciliary nerve enter the pericoroidal space a
short distance behind the limbus
• Connect with each other & conjunctival nerve
and form pericorneal plexus
• 60-80 myelinated branches pass into cornea sbj
31. NERVE SUPPLY
• After 1-2 mm lose myelin sheaths and divide into anterior and
posterior groups
• Anterior nerves (40-50) pass through stroma and form plexus
• subjacent to Bowman’s layer
• Nerve fibres then penetrate Bowman’s layer and form
subepithelial plexus
• Fibres then divide dichotomously to form a parallel network
• which run for upto 2 mm
• And give rise to fine free nerve terminals to superficial
epithelial layers
• The posterior groups of nerves (40-50) pass posteriorly to
• innervate the posterior stroma excluding Descemet’s
membrane
32. PHYSIOLOGY
• MAINTAINANCE OF TRANSPARENCY
• REFRACTION OF LIGHT
• CONTAIN INTRA OCULAR PRESSURE
• PROTECTIVE INTERFACE
33. TRANSPARENCY
• HISTOLOGICAL FACTORS:
MAURICE THEORY OF LATTICE ARRANGEMENT
GOLDMAN ET AL THEORY OF LATTICE SEPARATION
• PHYSIOLOGICAL FACTORS FOR CORNEAL TRANSPARENCY:
-stromal swelling pressure
-metabolic pump( Na K ATPase pump and bicarbonate dependant ATPase
pump)
-barrier function
-evaporation from the corneal surface
-intraocular pressure.
ALL LEADING TO DEHYDRATED STATE OF CORNEA
34. TRANSPARENCY
NON MYELINATED NEURONS
AVASCULARITY
ABSENCE OF PIGMENTS
Cellular factor affecting transparency
- keratocytes maintain transparency by producing
collagens and proteoglycans
- keratocytes contain enzymes involved in assembly of
stromal matrix
Specific enzyme defects are associated with corneal
opacification eg- mucopolysaccharidoses
35. METABOLISM IN CORNEA
• AEROBIC: GLYCOLYSIS EMB AND KREBS CYCLE
Total corneal oxygen consumption:9.5ml 02 /cm2 /hr
Rate of glucose consumption of cornea: 100mg/cm2/hr
90% being consumed by epithelium
• ANAEROBIC: HEXOSE MONOPHOSPHATE
PATHWAY
36.
37. Drug permeability across the Cornea
Factors affecting drug penetration through the
cornea :
1.Lipid and water solubility of the drug
2.Molecular size, weight and concentration of drug
3.Ionic form of the drug
4.pH of the solution
5.Tonicity of the solution
6.Surface active agents
7.Pro-drug form sbj
38. Aging changes in cornea
• By advancing age cornea becomes less translucent & dust like
opacities due to condensation in stroma.
• Bowman's & Descemet’s membranes also increase in
thickness .
• Arcus senilis is present due to infiltration of extra cellular lipid
and in almost every person over 60yrs.
• The small protrusion at the periphery of Descemet’s membrane
occur and known as Hassal Henle bodies and do not interfere
with vision.
