This lecture includes anatomy and Physiology of Cornea, if u like it kindly share it with colleagues and like it. I will share more lectures related to eye anatomy and optometry. Thank You.

3.  The cornea is the transparent avascular tissue
with a smooth, convex outer and concave
inner surface.
 front part of the eye that covers the iris, pupil,
and anterior chamber.
 It forms the anterior one-third of the eyeball.
Seen from the front
 Together with the lens, the cornea refracts
light, accounting for approximately two-
thirds of the eye's total optical power.
 In humans, the refractive power of the cornea
is approximately 43 dioptres.

4.  The cornea is composed of proteins and cells.
It does not have blood vessels, unlike most of
the tissues in the human body.
 Blood vessels may cloud the cornea, which
may prevent it from refracting light properly
and may adversely affect vision.
 The transparency of the cornea allows it to
refract light effectively.
 Since there are no nutrient supplying blood
vessels in the cornea, tears and the aqueous
humor in the anterior chamber provide the
cornea with nutrients.

5.  To meet the diverse functional demands the
cornea must be:
• Transparent
• Refract light
• Contain the intraocular pressure
• Provide a protective interface

6. Dimensions:
Although the dimensions of the cornea vary
considerably from one person to another.
 Anterior surface
Horizontal diameter:11.7mm
Vertical diameter:10.7mm
 Posterior surface:
Circular and measures about 11.7mm

7.  Thickness:
At center: 0.5 mm to 0.6mm
At periphery: 0.65mm to 1mm
 Surface area:
About 1.3 cm2 (one-sixth of the
globe)
 Optical Zone:
Cornea is almost a sphere, the
central 1/3rd is called optical zone
about 5.4 mm

8. Refractive power:
 Anterior convex surface has +48 dioptre
 Posterior concave surface has -5 dioptre
 Average power of cornea is +43 dioptre
Radius of curvature:
 Anterior convex surface is 7.8mm
 Posterior concave surface is 6.2 to 6.8mm
Refractive index:
 1.376

9.  The formation of cornea is induced by the
lens and the optic cup at the 7th weeks of
intrauterine life.
 Corneal epithelium- surface ectoderm
 Bowman's membrane- mesenchyme
 Stroma- mesenchyme and neural crest
 Decemets membrane- synthesized by
endothelium
 Endothelium- neural crest

10. Structure of cornea:
 Microscopically the cornea
consists of five layers.
From front to back.
1. Corneal epithelium
2. Bowman's layer (membrane)
3. Corneal stroma (substania
propria)
4. Descemet's membrane
5. Corneal endothelium

12.  The corneal epithelium:
forms the external layer and
interacts with the tear film and consists of five
layers of cells.
 It have fast-growing and easily
regenerated cells.
 Its total thickness measures about 50 to 60
microns.
 The superficial cells are flattened , nucleated,
non keratinized stratified squamous cells,
and deepest cells are columnar.

13.  Consists of 5 to 6 layers of
nucleated cells resting on
a basal lamina:
 Basal cells
 Wing cells
 Surface cells.
 At the corneoscleral
junction (limbus), the
epithelium becomes
thicker and may consist of
10 or more layers of cells.

14.  The healing process occurs rapidly, rate of
cell migration is 60-80μm/hr
 In case of total epithelial loss including total
limbus, cornea is covered with vascularized
conjunctival type of epithelium by adjacent
conjunctiva
 If small part of limbus with stem cell is
retained then conjunctival type of epithelium
is gradually disappear and metabolic behavior
of the corneal epithelium re-established very
slowly.

15. Bowman's layer (also known as the anterior
limiting membrane):lies immediately beneath
the basement membrane of corneal
epithelium.
 It measures about 8 to12 microns in
thickness. Bowman’s membrane ends
abruptly at the limbus.
 It is not a true elastic membrane but simply a
condensed superficial part of the stroma.
 Once destroyed, does not regenerate.

16.  Ultrastructuraly it is a felted meshwork of the
fine collagen fibrils of uniform size in a
ground substance
 Posteriorly it becomes blended and
interweaving with fibrils of anterior stroma
 Compact arrangement of collagen gives it
great strength and relatively resistant to
trauma both mechanical and infective

17. Substantia propria or stroma:
 About 500 μm thick, This forms about 90
percent of the corneal thickness. Transparent,
fibrous, and compact, it consists of many
lamellae of collagen fibrils that run parallel
with the surface.
 Small population of cells- keratocytes
present.

18. Descemet's membrane:
 This lies on the posterior surface of the
substantia propria and is the basement
membrane of the endothelium .
 The membrane is strong and homogeneous and
measure 10 micron in thickness.
 Its thickness varies with age, 3 micron at birth,
10-12 micron in adult, and 40 microns in old
age.
 While it is thicker than the endothelium.
 The peripheral rim of DM is internal landmark of
corneal limbus and also it is the anterior limit of
drainage angle, is called schwalbe line.

19. Endothelium:
 The corneal endothelium consists of single layer
of flattened cells that are polygonal in shape.
 Mechanism involves the pump function of the
endothelium through use of active sodium-
potassium adenosine triphosphatase (Na-K
ATPase) pumps that actively remove fluid that
leaks into the stroma from the aqueous
compartment.
 Nutrition to endothelium:
 Endothelium gets its nutrition and O2 from
aqueos
 Essential nutrients(such as glucose and amino
acids) pass across its surface to supply the
cellular needs of all the corneal layers.

20.  Fluid regulation: actively reducing the
osmotic pressure of stroma by metabolically
pumping the bicarbonate ions out of the
stroma to aquos.
 Endothelial repair:
 Physical and chemical damage to the
endothelium results in loss of cells
 Neighboring cells move over to fill the gap by
sliding process and enlargement of cells
occur
 Thus after injury the endothelial cell density
falls the cell area increases and the cell height
decreases.

21. Dua’s layer:
 According to a 2013 paper by Harminder
Singh Dua's group at the University of
Nottingham, is a layer of the cornea that had
not been detected previously.
 It is hypothetically
15 micrometres (0.00059 inches) thick, the
fourth caudal layer, and located between
the corneal stroma and Descemet's
membrane.

22. Corneal transparency:
Anatomical factors:
 Uniform and regular arrangement of corneal
epithelium.
 Regular arrangement of stroma.
 Corneal avascularity.
 Normal tear film.
Physiological factors:
 Relative state of corneal dehydration.
 Stromal swelling pressure.
 Normal intraocular pressure.
 Endothelium pump mechanism.

23. Corneal physiology:
 Protection against invasion of microorganism
into the eye.
 Acts as powerful refracting medium.
 Normally, more than 90% of the incident light
is transmitted through the cornea.
 This high percentage of transmittance is the
result of physical factors such as a smooth
anterior surface, uniform and regular
arrangement of the epithelial cells, closely
packed stromal lamellae of uniform size, and
the absence of vasculature.
 Protect intraocular contents.

24. Blood supply:
 Cornea is an avascular structure.
 Small loops derived from the anterior ciliary
vessels invade its periphery for about 1mm
and provide nourishment.
Innervation
 The cornea is one of the most sensitive
tissues of the body, as it is densely
innervated with sensory nerve fibres via
the ophthalmic division of the trigeminal
nerve by way of 70–80 long ciliary
nerves and short ciliary nerves.

25. Corneal nutrition and metabolism:
 Cornea requires energy for normal metabolic
activities as well as for maintaining
transparency and de hydration
 Energy is generated by the breakdown of
glucose in the form of ATP
 Most actively metabolizing layers are
epithelium and endothelium

26.  Sources of nutrients:
 Oxygen: mainly from atmosphere through tear
film, with minor amounts supplied by the aquous
and limbal vasculature.
 Glucose, amino acid, vitamins, and other
nutrients supplied to cornea by aqueos humour a
lesser amount from tears or limbal vessels
 Glucose also derived from glycogen stores in
corneal epethilium
 Epithelium consumes 02 10 times faster than
stroma.

27. Thank You