Cornea
Dr. Soujanya K, MBBS, MS, DNB, FPRS
Assistant Professor
YMCH
• Transparent
• Avascular
• fibrous coat
10.6 mm
11.7 mm
520
Micron
700
Micron
Lens of Power 45D
•
: Anterior Epithelium
•
: Bowman’s Layer
•
: Corneal stroma
•
: Descmets membrane
•
: Endothelium
Epithelium
Stratified squamous non keratinised
epithelium
Squamous
wing or umbrella
columnar
Bowman’s Layer
BOWMAN’S MEMBRANE
•
•
•
•
Acellular mass of condensed collagen fibrils.
12μm in thickness
Resistance to infection.
But once destroyed, it does not regenerate.
Stroma
500 Micron
collagen fibrils (lamellae) embedded in hydrated matrix of proteoglycans
Among the lamellae are present keratocytes, wandering macrophages, histiocytes
and a few leucocytes
Descemet's membrane
• strong homogenous layer
• It is very resistant to
chemical agents, trauma
and pathological processes.
Therefore, 'Descemetocele' can maintain the
integrity of eyeball for long.
DM remains in a state of tension and when torn
it curls inwards on itself
Endothelium
Hexagonal cells
DEHYDRATES THE CORNEA
CORNEA
ENDOTHELIAL PUMP
H2O
CORNEA- STARTS TO SWELL &
THICKENS
H2O
ENDOTHELIAL PUMP
• Blood supply
• Cornea is an avascular structure. Small loops
derived from the anterior ciliary vessels invade
its periphery for about 1 mm.
Normal
Abnormal
Nerve supply
• Cornea is supplied by anterior ciliary nerves
which are branches of ophthalmic division of
the 5th cranial nerve.
• After going about 2 mm in cornea the nerves
lose their myelin sheath and divide
dichotomously and form three plexuses — the
stromal, subepithelial and intraepithelial.
Why is cornea transarent?
•
•
•
•
Relatively dehydrated state,
Absence of blood vessels and pigment,
Uniform refractive index of all the layers
Uniform spacing of the collagen fibrils in the
stroma.
• The collagen fibrils are separated by a distance
which is less than the wavelength of light so
that any irregularly refracted rays of light are
eliminated by destructive interference.
• If there is an increase in separation of the
stromal collagen or a disruption in their regular
arrangement, for example, with an increase in
tissue fluid, the cornea becomes opaque.
NORMAL CORNEA
Each of the fibrils is separated from the
others by an equal distance.
CORNEAL EDEMA
orderly position of fibrils has been disturbed
Scattered light NOT eliminated
Elimination of scattered light by
destructive interference.
Cornea appears opaque or hazy
• This relative state of dehydration is maintained
by :
– the integrity of the hydrophobic epithelium and
endothelium,
– the endothelial pump and
– the osmotic gradient, because the aqueous and
tears are relatively hypertonic.
CORNEA
ENDOTHELIAL PUMP
H2O
1. Integrity of the hydrophobic epithelium and
endothelium
2. Endothelial pump
DEHYDRATES THE CORNEA
CORNEA
ENDOTHELIAL PUMP
H2O
CORNEA- STARTS TO SWELL &
THICKENS
H2O
ENDOTHELIAL PUMP
3. Osmotic gradient, because the aqueous and
tears are relatively hypertonic.
( Cornea)
(Aqueous humor)
(Tears)
Pathology
• The major pathological changes that occur are
broadly categorized as
– keratitis, and corneal 'ulceration‘
– 'scarring‘ and 'opacification'.
Superficial
keratitis
• Inflammation anterior to
Bowman's membrane
• epithelium and Bowman's
Deep
Keratitis
• Inflammation in the stroma
• Interstitial( Stromal)
keratitis
• Endothelitis
Superficial Keratitis
Interstitial
Deep
Endothelitis
Deep
Keratitis
Superficial
keratitis
Epithelial defect
Staining with1% sodium fluorescein dye
and viewed with cobalt blue filter
A loss of epithelium without any inflammation is
termed an epithelial defect. Also called abrasion or
erosion
Corneal ulcer
Infiltration
greyish haze or loss of
clarity.
A loss of epithelium with inflammation in the surrounding
cornea is called a corneal ulcer
corneal scar
• Final outcome of any inflammation.
• Unlike healthy transparent corneal tissue, scar
tissue is white and opaque in varying degrees
of severity
Opacification
Clinical feature
Terminology
Slight
details of the iris to nebula or a nebular
be seen through
corneal opacity
the opacity
Dense
details of the iris
cannot be seen
macula or a
macular corneal
opacity
Very Dense
white and totally
opaque obscuring
the view of the iris
and pupil
leucoma or a
leucomatous
corneal opacity
nebula
macula
Different grades of
corneal opacity
leucoma
Life is Like Cornea
Wealth is like corneal epithelium: it regenerates quite
rapidly.
Trust is like Bowman's membrane: once affected it leaves
a scar.
Ego is like stroma: the more it swells, the more problems
it causes.
Faith is like Descemet's membrane: it becomes denser
with age.
Respect is like endothelium: once lost, it is lost forever.
Dr. Uma Kulkarni