The document summarizes key aspects of corneal physiology: 1. It describes the structure and optical properties of the cornea, including its thickness, curvature, and role in refractive power. 2. The functions of the cornea are outlined as providing refractive power, protecting intraocular structures, and allowing images to reach the retina. 3. Factors like transparency, curvature regularity, and smoothness are described as affecting corneal function. Measurement techniques for analyzing the cornea's optical properties are also discussed.

1. Corneal physiology
OPTO : Ihsan Hmaid

3. Cornea
:Cornea characteristics
1.
2.
3.
4.
5.
6.
7.
Forms the anterior 1/6 of the outer tunic .
Completely transparent.
Avascular.
Ellipsoid and its vertical diameter is 11.5mm,and
Its horizontal diameter is 12mm.
It is more thick in periphery 0.67mm than in
center 0.52mm
It has smooth anterior and posterior surfaces .
Its radius of curvature is 7.8 mm in anterior
surface but 7mm in posterior surface.

4. Functions of the cornea
It is considered the main-1
.refractive surface of the eye
.Its power about 42 diopters
Protection of the intraocular-2
.structures of the eyes
Passage of images of objects to-3
.the retina

6. Factors affecting the corneal
function
. A - Transparency
.B - Regularity of curvature of its surface
.C - Smoothness of corneal surfaces

7. The optical properties of the human
cornea
Two major developments were made
because current measurement
techniques need improvement First,
the VU topographer, which uses a
color coded pattern, was validated
with real eye data showing better
performance compare to commercial
ring topographers particularly in

8. For example, ring topographers
underestimate astigmatism of the anterior
corneal surface by 4%. This
underestimation increases with complexity
of the surface. The astigmatism
underestimation was found to be 13% for
a post radially-keratotomized cornea.
Second, the aberration contribution of the
posterior surface was revealed using
Scheimpflug photography. Results show
that the contribution of the posterior
surface to corneal coma aberration is

9. On the other hand, on average the posterior
surface decreases corneal astigmatism by 31%.
Also the contribution of the posterior surface to
the spherical aberration of the cornea increase
with age reaching up to 15% at age 65. Thus,
measurement of the posterior surface is
necessary to specify corneal astigmatism and
spherical aberration accurately. The methods
introduced in this study are useful for
applications in laser refractive surgery, contact
lens fitting and studies on wave aberration of the
eye because it reveals the optical properties of
.the cornea more accurately

10. Corneal stroma

11. stromal hydration and its
regulation
Stromal hydration quantifies the water
component of the stroma. Its
regularization depends on different factors
which were detailed as; swelling pressure,
corneal endothelial and epithelial
metabolic pumps and barriers, tear film
evaporation and intraocular pressure.
Finally, the authors present different
clinical procedures for evaluating stromal
hydration, such as, the fluorophotometry
and hypoxic-stress. This study shows the

13. Corneal keratocytes (corneal
(fibroblasts
are specialized fibroblasts residing in the
stroma. This corneal layer, representing
about 85-90% of corneal thickness, is built
up from highly regular collagenous
lamellae and extracellular matrix
components. Keratocytes play the major
role in keeping it transparent, healing its
wounds, and synthesizing its components.
In the unperturbed cornea keratocytes
stay dormant, coming into action after any
. kind of injury or inflammation

14. Some keratocytes underlying the site of
injury, even a light one, undergo apoptosis
immediately after the injury. Any glitch in
the precisely orchestrated process of
healing may cloud the cornea, while
excessive keratocyte apoptosis may be a
part of the pathological process in the
degenerative corneal disorders such as
keratoconus, and these considerations
prompt the ongoing research into the
.function of these cells

15. Origin and functions
Keratocytes are developmentally derived
from the cranial population of neural crest
cells, from whence they migrate to settle in
the mesenchyme. In some species the
migration from neural crest comes in two
waves, with the first giving birth to the
corneal epithelium and the second
invading the epithelium-secreted stromal
;anlage devoid of cells

16. in other species both populations come
from a single wave of migration. Once
settled in the stroma, keratocytes
start synthesizing collagen molecules
of different types (I, V, VI) and
keratan sulfate. By the moment of eye
opening after birth the proliferation of
keratocytes is all but finished and
most of them are in the quiescent
. state

17. By the end of eye development an
interconnected keratocyte network is
established in the cornea, with
dendrites of neighbouring cells
contacting each over. Quiescent
keratocytes synthesize the so-called
crystallins, known primarily for their
role in the lens. Corneal crystallins,
like the lens ones, are thought to help
maintain the transparency and

18. They are also part of corneal
antioxidant defense. Crystallins
expressed by human keratocytes are
ALDH1A1, ALDH3A1, ALDH2 и TKT.
Different sets of crystallins are typical
to distinct species. Keratan sulfate
produced by keratocytes is thought to
help maintain optimal corneal
hydration; genetic disruption of its
synthesis leads to the macular

19. Corneal Transparency
The cornea is highly transparent tissue
with less 1% of light being scattered
within it. The cornea transparency is
maintained by two essential factors
the physical characteristics of the
cornea and controlled hydration also
there are other factors are important
.in corneal transparency

20. Stromal structure
The stroma is consist on based of lattice theory
which postulated the stroma consist from
collagen fibrils with small diameter and equal in
diameter and the proteoglycans occupy the
space between the collagen and keep the
collagen at constant distance from each other,
the separation between collagen fibrils is lees
than one –half on wavelength of light so that the
scatter light will elimination by destructive
interference in all direction of light except the
.one direction
(the direction of incident light)

21. Controlled hydration
It is the second factors important in
.determined the corneal transparency
The corneal hydration is controlled by to
layers corneal epithelium and
endothelium, both of these layers
possesses barrier function prosperity and
.metabolic function pumping
Not: hydration propriety of stromal is
determined by proteoglycans which
contributes fixed negative charge of

22. The physiological hydration of cornea is
maintained almost 78% if the cornea
allowed to _+ 5% swell of this value it
is being to scatter significant quantities
of light. The endothelium barrier to
free passage of molecule from
aqueous is formed focal tight junction
between the adjacent endothelium
cells, however in contrast to barrier of
endothelium the endothelium is lower
resistance to electronic ions and small
molecules, this leaky is offset by
metabolic pumping of ions out the

23. Also the epithelium contributes corneal
hydration control; it is act as barrier
effect on ions such as NA, CL
however in contrast to barrier of
endothelium is lower resistance to
water diffusion. When the cornea
swells by water the light scattered
increase with ensued transparency
loss due to disruption of regular
.collagen fibrils

24. The other factors maintain corneal
:transparency
.Corneal an avascular-1
Unmyelination of corneal nerve-2
.fibers
.Degeneration of epithelium-3
integrity of this layer and all layers of
((cornea
Higher difference between refractive-4
.index of cornea and air

25. Corneal Metabolism
It is the series of chemical reaction that
place in living tissue. Where the constant
metabolic activity in cornea is necessary to
maintain on transparency, temperature
((and hydration of cornea 78%
The metabolic occur in epithelium and
endothelium, the main substance for this
metabolic is glucose, oxygen, amino acid
. and vitamin

26. Due to an avascular of cornea promotes to
alternative routes of metabolic supply
there are three possibilities one from
aqueous second from atmosphere via tear
.film third from perilimbal blood vessels
The oxygen is mainly derived from
atmosphere via tear film, in under steadystate the assume tear are saturated with
oxygen and therefore the tension of
oxygen crosspending to atmosphere is
155 mm hg at sea level in the open eye
and when eye closed the tension is about
55 mm hg in this state the oxygen supply

27. The consumption rates of oxygen for
layers of the cornea are not equals is
as follog 40, 39, 21 epithelium,
.stroma, endothelium respectively
The glucose is derived from aqueous;
the cornea derives the energy from
the oxidative breakdown of
carbohydrates and the glucose is
primary substrate for generation of
adenosine triphosphate is catabolized
.by two metabolic pathways as follog

28. Glycilytic ( Embden Meyerhofpathway) followed by Krebs
.tricarboxylic or citric acid cycle
Hexose monophosphate (pentose)- .
phosphate
The first step in glucose is
phosphorlyation into glucose-6:phosphate

29. :E
mbden M
eyerhof pathway - 1
This the major one which account for
about 85%, in this stage the enzymes
called dehydrogenises act as catalysts
for each in this process, in this
process the glucose molecule is split
into two molecules of pyruvic acid, in
third of four stages of glycolytic
process liberated energy is used to
form two molecules of ATP from ADP
and inorganic phosphate. If occur
under aerobic condition six additional

30. while under anaerobic condition two
molecules are only produce, in this
state the pyruvic acid is convert into
lactic acid without any significant
energy where the lactic acid is build
up in stroma and sufficient process is
created to allow to water to drawn into
stroma faster than endothelium
pumping so that can occur stromal
edema, this because the little energy

31. In aerobic condition of glycolytic
doesn’t stop in stage of produce lactic
acid but continues until the final
products are carbon dioxide and
water this called Krebs tricarboxylic
acid cycle or citric acid during this
cycle the carbon dioxide and
hydrogen atoms are released the
hydrogen atom at length become
oxidative to form water and total
oxidative process synthesize further
.30 ATP molecules

32. :H
exose monophosphate- 2
Although the glycolytic pathway is
principle pathway for oxidative of
glucose but there other available of
these the hexose monophosphate
.shunt is the most important
In this state or pathway the glucose-6phosphate is directly oxidative into
carbon dioxide and water with energy
.of 35 ATP molecules

33. T effect of contact lenses on corneal
he
metabolism
Contact lens presents barrier between
the cornea and atmosphere
therefore Contact lens deprivation
of oxygen to enter into cornea
and consequently reduction in
.aerobic glycolysis

34. Normally this situation is avoided
with hard corneal lenses because
they move and produced tears
circulation this permitting some
degree of oxygen and carbon
dioxide exchange between the
.cornea and atmosphere

35. Soft contact lenses also move on the
eye but the circulation of the tear
under soft contact lens is less
although they have the advantage of
transmission o oxygen in amount
varying with the nature and thickness
of materials but with sclera lenses
tear exchange is less. The cornea
can tolerated levels as low as 11-19
.mm hg

36. Corneal sensitivity
The sensitivity of the corneal is
probably unsurpassed by that of any
part of the body. Its varies from a
maximum apically to a minimum at
the peripheral with considerable drop
in sensitivity at limbus. Sensitivity of
the cornea is reduce with age, The
peak sensitivity found in young

37. Sensitivity also varies with iris color, in
this the blue-eye color have a greater
sensitivity than those with dark –
brown color. Sensitivity is the same in
both eye and sexes in the normal
. circumstance

38. Corneal display a diurnal variation in
sensitivity with about third greater
sensitivity as the day progresses from
morning to evening. Diabetic,
Albinism, and all disease affecting the
cone of the corneal causes reduction
.in sensitivity

39. The corneal temperature
The central has a temperature of 34°C,
which appears to increase towards
the periphery and is found to be
nearly 0.50°C warmer at the limbus.
The cooling of the cornea follog a
blink seems to be slower in those who
. exhibit a lower blink rate than normal

40. The normal corneal temperature may
alter during contact lens wear.
Corneal temperature can be
measured by a wide-field, colourcoded infra-red imaging device, and a
.thermography-visual-system

41. Endothelium
every 1mm2
has 2800 – 3200
endothelial cell. The
whole number is about
500000 cells which has
.a hexagonal shape
Endothelium
hexagonal shape

42. corneal endothelium
The corneal endothelium is a single
layer of cells on the inner surface of
the cornea. It faces the chamber
formed between the cornea and the
.iris
It is a monolayer of specialized,
flattened, mitochondria-rich cells that
lines the posterior surface of the

43. The corneal endothelium governs fluid
and solute transport across the
posterior surface of the cornea and
actively maintains the cornea in the
slightly dehydrated state that is
.required for optical transparency

44. Hexagonal cells of corneal endothelium visualized by specular
microscopy.

45. Physiology of corneal endothelium
The principal physiological function of
the corneal endothelium is to allow
leakage of solutes and nutrients from
the aqueous humor to the more
superficial layers of the cornea while
at the same time actively pumping
water in the opposite direction, from
the stroma to the aqueous. This dual
function of the corneal endothelium is

46. Since the cornea is avascular, which
renders it optimally transparent, the
nutrition of the corneal epithelium,
stromal keratocytes, and corneal
endothelium must occur via diffusion
of glucose and other solutes from the
aqueous humor, across the corneal
. endothelium

47. The corneal endothelium then actively
transports water from the stromalfacing surface to the aqueous-facing
surface by an interrelated series of
active and passive ion exchangers.
Critical to this energy-driven process
is the role of Na+/K+ATPase and
carbonic anhydrase. Bicarbonate ions
formed by the action of carbonic
anhydrase are translocated across
the cell membrane, allowing water to

48. Vertical section of human cornea from near
.the margin
(Corneal endothelium)

49. Endothelial physiology and intraocular lens
.implantation
The endothelium is the cellular
monolayer which lines the posterior
surface of the cornea. This layer is
important in clinical ophthalmology
because it is vital to maintenance of
the transparency of the cornea and
vision through its pump and barrier
functions which limit the ingress of
fluid into the cornea from the

50. When the function of the corneal
endothelium becomes compromised,
the corneal stroma swells as it
hydrates. Subsequently, epithelial
bullae form with painful recurring
epithelial erosions, and finally corneal
scarring and blindness result. The
relatively vulnerable position of the
corneal endothelium renders it
susceptible to iatrogenic injury during
intraocular procedures, especially IOL
implantation: the poor regenerative

51. The functional reserve of corneal
.endothelium
With recent advances in our knowledge
of corneal physiology, coupled with
the development and increasing
availability of the specular microscope
as a clinical instrument, valid
observations relating the morphologic
appearance of the corneal
endothelium to its functional capacity

52. Manual methods of data analysis are
cumbersome, time consuming, and
associated with human error and
investigator bias. The Omnicon
pattern analysis system lends itself to
objective analysis of morphologic
features, offers the possibility of
quantifying the data obtained and,
hopefully, will lead to a better
understanding of the many aspects of
endothelial cell morphology which, in
total, relate to the functional reserve
. of a given cornea

54. Epithelium
Embryologically, the corneal epithelium
is derived from surface ectoderm at
approximately 5–6 weeks of
gestation. It is composed of
nonkeratinized, nonsecretory,
stratified squamous epithelium, which
is 4–6 cell layers thick (40–50 μm).
The epithelium is covered with a tear
film of 7 μm thickness, which is

55. Corneal epithelium

56. Without this film, degradation of visual
images results. The tear−air interface,
together with the underlying cornea,
provides roughly two thirds of the total
refractive power of the eye. The
mucinous portion of tears, which
forms the undercoat of the tear film
and is produced by the conjunctival
goblet cells, interacts closely with the
corneal epithelial cell glycocalyx to
allow hydrophilic spreading of the tear
. film with each eyelid blink

57. Referances
http:/www.acuvue.co.in/
/
acuvue-life/
health-file/
aboutyour-eyes/
physiology-of-the-eye.html
http:/www.ncbi.nlm.nih.gov/
/
pubmed/
673339
2.
http:/palopticlub.com/ forumdisplay.php?f=10
/
vb/
3.
http:/dare.ubvu.vu.nl/
/
handle/
1871/
10864
4.
http:/en.wikipedia.org/
/
wiki/
Corneal_keratocyte
5.
1.

58. Thank you