cornea

1. ANATOMY , PHYSIOLOGY ,
PATHOLOGY OF CORNEA
DR.K PADMAVATHI.MS DGO
ASST.PROF.OPTHAL

2. Anatomy Of Cornea
 Cornea – transparent , comprising one-sixth
of the anterior eye ball.
 Junction of cornea with sclera – Limbus
which is marked by shallow sulcus called
Sulcus Sclerae .
 Convex forwards , but when seen from front
Elliptical(horizontal diameter>
vertical diameter)

4. Anatomical Dimensions of cornea
Corneal
diameter(mm)
Radius of
curvature
(mm)Horizontal vertica
l
Anterior
surface
11.7 10.6 7.8
Posterior
surface
11.7 11.7 6.5

5. Corneal Thickness :
 More in the periphery (1.2mm)than in
the centre(0.5-0.6mm).
 Affected by – Age
Temperature
Osmolality of tears
Integrity of epithelium &
endothelium
Intraocular Pressure
Disease & Drugs

6. Histology of Cornea:
 Histologically , Cornea has 5 layers
 They are – Epithelium
Bowman’s layer or
membrane
Substantia Propria or
stroma
Descemet’s membrane
Endothelium.

7. Histology of Cornea:

8.  Cornea is - Avascular
- Devoid of lymphatic
channels
- Cells derive nourishment
by diffusion from the
aqueous , the capillaries at
the limbus and oxygen
dissolved in the tear film.

9. Nerve supply :
• Long Anterior ciliary nerves – branches of
ophthalmic division of Trigeminal nerve.
• These nerves run in the perichoroidal
space and after going about 2mm in
cornea, the nerves lose their myelin
sheaths and divide dichotomously to form 3
plexuses – stromal (annular) , sub epithelial
, intraepithelial corneal plexuses.
• No specialized nerve endings or sensory
organelles.
• Axons do not have schwann cell sheath .
These naked axons are responsive to pain
& temp.

10. PHYSIOLOGY OF CORNEA
Metabolism of cornea : mainly aerobic.
• can function upto 6 to 7 hrs anaerobically
under normal conditions.
• Endothelium , Epithelium , Stromal
keratocytes – metabolically active cells.
• Oxygen supply – from tear film with a
small contribution the limbal capillaries.
• Oxygen gradient is from tears to
aqueous
• Glucose supply – 90% from aqueous &
10% by limbal
capillaries .

11. • Cornea – most refractive surface .
Refractive index – 1.38 .
• Tear film – 3 layers
1. Superficial lipid layer decreases
2. An aqueous layer evaporation
3. Inner mucin layer – lines the
hydrophobic epithelium and makes it
wettable
• Tear film maintains healthy normal
environiment for the corneal epithelial
cells.

12. • Transparency of cornea : due to
- its relatively dehydrated state , absence of
blood vessels & pigment , uniform refractive
index of all layers , uniform spacing of collagen
fibrils in stroma .
• If there is an increase in seperation of stromal
collagen or a disruption in their regular
arrangement (for ex: with increase in tissue
fluid ), the cornea becomes opaque.
• This relative state of dehydration is
maintained by – integrity of epithelium and
endothelium , endothelial pump , osmotic
gradient .
• The main role of endothelial cells is to limit the
fluid intake of cornea from aqueous .

13. Functions of cornea :
1. Allowing transmission of light by its
transparency .
2. Helping the eye to focus light by refraction.
3. Maintaining structural integrity of the globe.
4. Protecting eye from infective organisms,
noxious substances, & UV radiations.
• Effect of Age : with advancing age ,
- the cornea becomes less transparent and
develops dust like opacities due to
condensations in the deeper parts of cornea.
- increase in thickness of Bowman’s and
Descemet’s membranes .

14. What happens if cornea sustains injury:
 If injury is superficial , involving only epithelium –
the stratified squamous epithelium rapidly
regenerates.
 Regeneration of corneal epithelial cells – from stem
cells(epithelial cells present as Palisades of Vogt at
the limbus). These are mitotically active cells with
an increased surface of basal cells present in folds
and palisades .
 At the centre of cornea , there is very little mitotic
activity in the basal cells .
 Bowman’s layer – condensed part of the anterior
most layer of the stroma , serves as a barrier to the
underlying stroma .
when damaged , it does not regenerate , but
replaced by fibrous tissue , as is the stroma .

15. • Descemet’s membrane – basement membrane
of the endothelial cell layer .
when injured , can be regenerated by
endothelial cells.
It is strong and generally resistant to trauma,
but if severe can develop tears or ruptures .
It is elastic and if torn , the edges separate and
are visible as parallel lines or if disinserted ,
curls up in anterior chamber .
• Endothelial cells are closely bound to each
other and entire endothelium can be stripped
off as sheet.
The corneal endothelial cells does not
regenerate but adjacent cells slide to fill in a

16. • The corneal epithelium and endothelium maintain
a steady fluid content of the corneal stroma .
They are lipid rich and hydrophobic with good
solubility to lipids and water , but poor to salts .
• The stroma is hydrophilic .
• Epithelial cells – have junctional complexes –
prevent the passage of tear fluid into the cornea
and loss of tissue fluid from the cornea into the
tear film .
• Junctional complexes – seen in endothelium too.
• Na+-K+- ATPase pump system – limits the influx
of aqueous humour into the cornea .
• Trauma to either of these layers produces
oedema of the stroma .
• The dense Bowman’s layer , however , tends to
limit the spread of fluid from the damaged

17. Permeability of the cornea :
• Lipids in cell membrane – have poor
permeability to salts and are
hydrophobic.
- help in maintaining the relative state of
dehydration (important for corneal
transparency).
• The osmotic gradient between cornea
and hypertonic tears anteriorly and
aqueous posteriorly limits movement of
water into cornea .
• The hydrophilc stroma has better

18. • The cornea is normally avascular .
• In case of infection and inflammation, new blood
vessels from limbus invade cornea and bring
humoral & cellular defence mechanism to the
inflamed site for the purpose of immunological
defence and repair .
• The new vessels arising from conjunctival
superficial vascular plexus or deep plexus from
the anterior ciliary arteries , normally end as
loops at the limbus .
• But, on stimulation , new vessels can invade
cornea . When stimulus is eliminated , the new
blood vessels atrophy , regress , and become
empty leaving behind “ghost ”vessels . Thus, the
corneal transparency is lost and corneal opacity

19. • The cornea is prone to atmospheric
influences(smoke , dust , heat , dry air &
sand ) which can affect the ocular
surface.
• Excessive exposure to UV radiation –
harm the cornea – leads to solar
keratopathy , pteygium , climatic droplet
keratopathy .
• Vitamin A deficiency – weakens
defences and healing potential .
• Poor hygiene – assists the spread of
infection by eye to eye infection .
• Hereditary disorders , Dystrophies &
other degenerations can also affect the

20. PATHOLOGY OF CORNEA
• The major pathological changes – keratitis ,
corneal ulceration , scarring & opacification.
• Keratitis : refers to any type of corneal
inflammation .
• Superficial Keratitis : Inflammation anterior
to Bowman’s membrane .
Superficial punctate keratitis : superficial
keratitis , if occurs in discrete patches .
• Deep keratitis : inflammation in the stroma
.
further categorized as Stromal or Interstitial
or Endothelitis , depending on direct

21. Keratitis

22. Corneal Ulceration :
• A loss of epithelium is termed epithelial defect.
• Can be demonstrated by staining with 1%
sodium fluorescein dye and viewed with cobalt
blue filter light .
• Abrasion or Erosion- the epithelial defect , if
superficial without inflammation .
It usually heals within 12 to 24 hrs by
regeneration of the epithelial cells from the
periphery , which slide over to cover the defect .
• Corneal Ulcer- epithelial defect with
inflammation in the surrounding area . May be
infective or sterile .
Inflammations in the cornea is visible as a
greyish haze or loss of clarity .
If accompanied by an outpouring of leucocytes ,
the appearance is more off – white or yellowish ,

23. Corneal Ulceration

24. Scarring :
• Corneal Scar – final outcome of any
healthy tissue .
• Scar tissue – white and opaque with
varying degrees of severity , unlike
normal healthy corneal tissue .
• Nature , Extent , Pattern & Density of
scarring vary according to the nature
of original inflammatory diseases .

25. Corneal Opacity :
• Corneal scar results in opacification .
• If details of Iris are seen through the opacity , it is
called Nebula or Nebular Corneal Opacity .
• If Opacity is more dense , through which the details
of Iris cannot be seen but , the Iris and pupillary
margins are visible ,it is called Macula or Macular
Corneal Opacity.
• If very dense and white & totally opaque obscuring
the view of Iris & pupil , it is called Leucoma or
Leucomatous Corneal Opacity.
- If Iris is adherent to the back of leucoma following
healing of a perforated corneal ulcer – Adherent
Leucoma .
- if Iris tissue is incarcerated – and incorporated
within the scar tissue , then ,
Corneoiridic scar.
- or if ecstatic , an Anterior

26. Corneal Opacity

27. Corneal odema :
• Can affect entire cornea . But , generally manifests
itself in epithelium , which becomes steamy , an
appearance due to the accumulation of fluid between
the cells , especially the basal cells .
• The accumulation of fluid between the lamellae and
around the nerve fibres of the stroma produce
haziness through out the entire cornea due to
alteraton in the refractive condition .
• Vesicular / Bullous keratopathy : when
oedema lasts for long period , the epithelium tends to
be raised into large vesicles or bullae .
Intense pain & symptom of ocular Irritation as the
Bullae periodically burst .
• Striate keratopathy : form of cornea oedema
seen after operations upon the globe in which a
peripheral corneal section has been made , as in
corneal extraction .

28. Corneal oedema

29. Filamentary Keratopathy :
• Is formation of epithelial threads(corneal filaments )
which adhere to the cornea by one end while the
other , which is often club shaped , moves about
freely .
• Such filaments produce symptoms of irritation and
foreign body sensation .
• Occurs in degenerative conditions , in long standing
corneal oedema ,in cases of viral keratitis (herpetic
type) , in collagen vascular diseases , in dry eyes due
to any cause .
Keratic Precipitates : initially keratitis punctata or
‘k.p’.
• These are depositions of leucocytes and other cells
on the back of cornea in Cyclitis , Iridocyclitis , and
occasionally in Choroiditis .
• They may be on back of clear cornea or the deeper
layers may be infiltrated as a result of intraocular

30.  Filamentary
keratopathy
 Keratic
precipitates

31. Hypopyon:
• Consists of polymorphonuclear leucocytes
which accumulate in the lower angle of
anterior chamber and eventually become
enmeshed in a network of fibrin .
• It is seen in severe corneal ulcers as a
collection of pus in the anterior chamber .
Prominent or Enlarged cranial nerves :
• May be asymptomatic and detected
accidentally or may be associated with other
local disease conditions such as
keratoconus.
• The corneal nerves are known to be
enlarged in MEN Type 11b syndrome
(combination of carcinoma of thyroid ,
phaeochromocytoma , mucosal neuroma ,
and possibly marfanoid habitus .

32. Hypopyon