SlideShare a Scribd company logo
1 of 49
CORNEAL
TRANSPARENCY
1
HIRA NATH DAHAL
Transparency is the quality or state of
transmitting light without appreciable
scattering so that bodies lying beyond are
entirely visible .
2
The cornea is an exquisite layered composite
material with a structure ideally suited to its
function as the transparent window in the tough
outer tunic of the eye ball through which the
outside world is viewed.
3
The Cornea is a transparent avascular tissue with
smooth outer convex surface and concave inner
surface which resembles a small watch glass.
Forms anterior one –sixth of the fibrous
coat of the eye.
4
Corneal Dimension
Horizontal Vertical
Anterior surface-- 11.7mm 10.6mm
Posterior surface-11.7mm 11.7mm
Radius of curvature
Ant surface-7.8mm Post surface-6.5mm
Corneal thickness
Central-0.5-0.6mm Peripheral-1-1.2mm
5
Functions of Cornea
Optical : It forms the principal refractive surface
accounting for some 70%(40-45 D) of total refractive
power(60D).
Barrier: Cornea provides a protective interference with
the outer environment and also contain intraocular
pressure.
6
Layers of cornea
Epithelium.
Bowman layer.
Lamellar Stroma.
Descemet’s membrane.
Endothelium.
7
1. Epithelium (50-90 um)
3 types of cell :-
i) A single layer basal columnar cells stand as paliside like manner in
perfect alignment on the basement membrane.
Attached by hemidesmosomes to the epithelial basement membrane.
ii)2- 3 rows of wing cells.
iii) 2 layers of flattened surface cells
- microplicae and microvilli
- excellent ability to regenerate
- attached by desmosomes , and zonulae occludens
8
9
BIOCHEMICAL COMPOSITION OF
EPITHELIUM
Water (70% of wet weight) .
Protein synthesis is 5 times higher than stroma.
Lipid (Phospholipid and cholesterol).
Enzymes.
ATP,glycogen,glutathione,Ascorbic acid.
Acetylecholine, cholinesterase.
Electrolytes (K+,Na+,and Cl– ).
10
2. Bowman’s layer (8-14 um):
Acellular mass of condensed collagen fibril.
It is not true elastic membrane but simply continuation
of stroma.
Shows considerable resistance to infection and injury
Does not regenerate.
11
3.3. Lamellar Stroma (0.5mm):(0.5mm):
Consists collagen fibrils (lamellae) (200-250)and cells embedded in matrix
(proteoglycans).
Mean diameter of collagen fibril between
22.5&32nm,predominantly type I collagen.
 Fibril within the lamellae are parallel to each other & also parallel to corneal
plane
Fibril within adjacent lamellae make various angles with respect to one other.
12
 Stromal cells are keratocytes, wandering
macrophages, histocytes etc.
 Keratocytes are fibroblast which produce ground
substance (keratin & chondrotin sulfate) and collagen
fibril.
The highly negatively charged keratin sulfate around
collagen fibril maintain spatial relationship between
them.
13
BIOCHEMICAL COMPOSITION OF STROMA :
-Water(78%)
- Collagen (15%)
- other protein (5%)
- Glycosaminoglycan
# Keratan sulfate(0.7%)
# Chondroitin sulfate(0.3)
# Chondroitin
- Salts
14
4.4. Descemet’s membrane (3-40um):(3-40um):
Homogeneous layer.
Made up of collagen & glycoprotein.
Resistant to chemical agent, trauma infection and
pathological process .
Can regenerate.
15
5.5. Endothelium ::
-- Single layer polygonal cells
- Attached to Descemet’s membrane by
hemidesmosomes and laterally to each other
by tight junctional complex .
- barrier function is calcium dependent
-Contains active pump mechanism
-Involved in active secretion and protein
synthesis
16
17
FACTORS AFFECTING CORNEAL TRANSPERANCY
Anatomical factors:
* Uniform & regular arrangement of corneal
epithelium .
* Peculiar arrangement of corneal stromal lamellae.
* Corneal avascularity.
Physiological factors:
Relative state of corneal dehydration.
Anatomical factors
18
1. Corneal epithelium
 Epithelial cells are closely packed.
 Uniformity & regularity in arrangement.
 Homogenicity in refractive index.
 Tight intercellular junction.
19
2. Tear film
 Keeps epithelial surface smooth.
 Provides high quality optical surface.
20
3.3. Arrangement of stromal lamellae:
Maurice Theory:
Collagen fibrils of uniform diameter (275-
350Å)are packed regularly and thus
creates a lattice pattern.
 The fibril axis are located at the position
of a perfect crystalline lattice.
 Interfibrillar spacing is about 50-60nm
and is smaller than wavelength of light
(400-700nm).
 Scattered light is destroyed by mutual or
destructive interference
21
Interference:
Interference is the phenomenon by virtue of which
there is a modification in the distribution of energy due
to superimposition of two or more waves.
‘ Principle of superimposition’. This can be stated as: “
Whenever two or more sets of waves pass through and
cross one another in the same medium, they behave
independent of each other and net displacement of a
particle , at any instant , is equal to the algebraic sum of
the individual displacements due to all the waves.”
22
Interference may be ‘constructive’ or ‘destructive’
In constructive interference the crest of one wave coincides with
the crest of another and the net amplitude is equal to the sum of
individual amplitudes.
In destructive interference the crest of one wave coincides with the
trough of another and the net amplitude is equal to the difference
between the individual amplitudes.
Scattered rays - destructive interference
Rays on the line of incident
light- Constructive interference
23
Destructive interference
24
LATTICE ARRANGEMENT
SWOLLEN CORNEA
Findings contradictory to Maurice theory
i) The cornea is not perfectly transparent, otherwise an
ophthalmologist could not view cornea in the slit lamp..
ii) Shark’s cornea with regions of disorganised fibres and
random distribution of interfibrillar distances is also quite
transparent.
.
25
Hard core cylinder model of Twersky:
Twersky proposed a model in which the fibrils had a composite
structure consisting of an inner core, composed of collagen fibrils
and outer coating of a material that matches the refractive index
of the ground substance. The coating would increase correlations
but not affect the light scattering properties of a fibril.
The loss of transparency observed when the cornea swells would
be explained in the hard core model on the basis of increased
area available per fibril.
26
Theory of Goldman & Benedek :
Fibrils are small in relationship to
wavelength of light and do not interfere
with light transmission unless they are larger
then one-half of a wavelength of light
(2000Å).
27
4. Endotheliumis transparent because it is
* Single layer.
* Homogeneous.
* Closely packed cells .
* It has deturgescence function.
28
5. Corneal Vascularisation:
Except for capillary palisade of limbus, normal cornea is
avascular.
Corneal avascularity factors are not known.
When vessels present are due to corneal pathology.
Vascularisation -Loss of transparency.
29
Mechanical Theory : According to Cogan (1948)
 Blood vessel can not invade normal cornea.
 Loosening of compactness of corneal tissue
due to oedema is a must for neovsacularisation.
Interstitial keratitis where oedema always precedes
vascularisation.
Some vesostimulatory factor may be needed along with
corneal oedema for neovascularisation to occur.
30
Chemical theory:
Role of vasoinhibitory factors(VIF)
Sulfate ester of hyaluronic acidSulfate ester of hyaluronic acid
Role of vasostimulatory factors (VSF)
Low mol wt. AminesLow mol wt. Amines
Corneal hypoxia→VSF stimulation→ Neovascularisation
31
Physiological factors
32
Corneal hydration :
Normal cornea maintains itself in a state of relative dehydration (80% water
content ) which is essential for corneal transparency.
It is kept constant by---
1) Factors which draw water in the cornea, like
-Stromal swelling pressure (SP)
-Intraocular pressure (IOP)
2 ) Factors which prevent flow of water in the cornea
- Mechanical barrier function of epithelium &
endothelium.
3) Factors which draw water out of cornea
-active pumping action of endothelium.
33
FACTORS AFFECTING CORNEAL HYDRATION:
i) STROMAL SWELLING PRESSURE (SP, 60 mmHg):
Pressure exerted by glycosaminoglycans(GAGs) of
the corneal stroma which act like a sponge.
Electrostatic repulsion of the anionic charges on
the GAG molecule expands the tissue, sucking in the
fluid with equal but negative pressure called,
imbibition pressure (IP).
34
In vitro, IP=SP
In vivo, IP is reduced by values
equivalent to IOP.
i.e. IP=IOP- SP
i.e. IP=17-60= - 43mmHg.
Negative imbibation pressure
draws out water from stroma.
35
ii) Barrier function of epithelium and endothelium:
Epithelium & endothelium are semipermiable in nature.
Function as barriers to excessive flow of water and
diffusion of electrolytes into the stroma.
Epithelium offers most resistance to flow of water.
36
iii) Hydration control by active pump mechanism:
a) Na+
/K+
ATPase pump system:
•Endothelium is more active than &epithelium,
•Pumps are located in basolateral membrane of endothelial cell.
•Stromal transparency develops 13-20 days after birth due to greatest increase in
pump sites/cell.
37
•Enzyme “Na+
/K+
activated ATPase” mediate pump causes extrusion of the Na+
& water from the stroma and thus maintain corneal transparency.
•Corneal hydration depend on extent to which endothelial barrier and pump
function can be reestablished.
38
b) Bicarbonate dependent ATPase present in endothelium are also reported to have
role in
fluid /ion balance in the cornea.
c) Carbonic enhydrase enzyme catalyzes the conversion of CO2and water
into HCO3
-
and H+
, thus provides important source for HCO3
-
for endothelial
pump.
d) Na+
/H+
pump has also been postulated.
39
40
Corneal thickness is increased and transparency is
decreased when there is endothelial damage and to a
lesser extend when epithelium is damaged.
41
iv) Passive ion movement, like
- K+
, Cl-
and HCO3
-
ions diffuse into
aqueous humor.
- Na+
, Cl-
and HCO3
-
diffusion in
contra lateral direction.
42
v) Hypoxia, pH and changes in the temperature
can alter the metabolic activity of the cornea and
thereby may cause alteration in corneal thickness
and loss of transparency.
43
vi) Intraocular pressure (IOP) :
As we know ,
I P = IOP - SP, i.e. 17- 60= - 43 mmHg,
i.e. I P is a negative pressure.
When IOP exceeds SP, i.eWhen IOP exceeds SP, i.e. when I Pwhen I P becomes positive , corneal oedemabecomes positive , corneal oedema resul
It can occur when there is
- high IOP and normal SP,as in acute glaucoma,
- Normal IOP and low SP, as in endothelial dystrophy.
44
45
Corneal Swelling:
Electron micrograph of a swollen cornea shows fibril
distribution with region completely devoid of fibrils.
These voids are called lakes, which have larger dimensions &
spoils the interference that is critical to transparency.
46
Photorefractive keratectomy using argon fluoride excimer
laser:
. Despite the excimer laser’s ability to ablate corneal tissue
with good precision and with little collateral damage, the
treatments commonly result in the development of increased
subepithelial light scattering that gives the cornea a hazy
appearance in the treated area.
increased numbers of activated keratocytes and vacuoles within
and around keratocytes adjacent to the treated area. Activated
keratocytes may have different effective refractive indices than
normal keratocytes, thus increasing their contribution to
scattering. Vacuoles within and around keratocytes may act like
the lakes seen in swollen cornea.
47
vii) Evaporation of water from corneal surface:
Evaporation of water from the pre-corneal tear film fluid →
increase in osmolarity relative to cornea→hyper tonicity of
tear film → flow of water from the cornea.
48
Corneal transparency results from-----
Interference among the residual waves scattered
by different fibrils.
The inefficiency of the fibrils as scatters.
Avascularity of the cornea.
The thinness of cornea which is maintained by a
complex series of metabolically dependent reaction
in the corneal endothelium and epithelium.
49

More Related Content

What's hot

Pseudophakia
PseudophakiaPseudophakia
Pseudophakia
arya das
 
Eyelid anatomy and physiology
Eyelid anatomy and physiologyEyelid anatomy and physiology
Eyelid anatomy and physiology
Najara Thapa
 

What's hot (20)

Anatomy of uvea
Anatomy of uveaAnatomy of uvea
Anatomy of uvea
 
anatomy And Physiology of tear film
anatomy And Physiology of tear film anatomy And Physiology of tear film
anatomy And Physiology of tear film
 
Tear film test
Tear film testTear film test
Tear film test
 
Physiology of cornea
Physiology of corneaPhysiology of cornea
Physiology of cornea
 
Presbyopia
PresbyopiaPresbyopia
Presbyopia
 
purkinje images
purkinje images purkinje images
purkinje images
 
EXTRA OCULAR MUSCLES PHYSIOLOGY
EXTRA OCULAR MUSCLES PHYSIOLOGYEXTRA OCULAR MUSCLES PHYSIOLOGY
EXTRA OCULAR MUSCLES PHYSIOLOGY
 
Pseudophakia
PseudophakiaPseudophakia
Pseudophakia
 
Eyelid anatomy and physiology
Eyelid anatomy and physiologyEyelid anatomy and physiology
Eyelid anatomy and physiology
 
Sclera
ScleraSclera
Sclera
 
MYOPIA
MYOPIAMYOPIA
MYOPIA
 
Accommodation of eye
Accommodation of eye Accommodation of eye
Accommodation of eye
 
Angle of anterior chamber
Angle of anterior chamberAngle of anterior chamber
Angle of anterior chamber
 
Direct ophthalmoscopy
Direct ophthalmoscopyDirect ophthalmoscopy
Direct ophthalmoscopy
 
VISUALACUITY CHARTS
VISUALACUITY CHARTSVISUALACUITY CHARTS
VISUALACUITY CHARTS
 
Vitreous humour
Vitreous humourVitreous humour
Vitreous humour
 
Aphakia
AphakiaAphakia
Aphakia
 
Macular function tests
Macular function testsMacular function tests
Macular function tests
 
Anisometropia
AnisometropiaAnisometropia
Anisometropia
 
Accommodation: Theories and Mechanism
Accommodation: Theories and MechanismAccommodation: Theories and Mechanism
Accommodation: Theories and Mechanism
 

Similar to Corneal transparency

anatomy and physiology of cornea-.pdf gfhh
anatomy and physiology of cornea-.pdf gfhhanatomy and physiology of cornea-.pdf gfhh
anatomy and physiology of cornea-.pdf gfhh
epicsoundever
 
Corneal physiology ‫‬
Corneal physiology ‫‬Corneal physiology ‫‬
Corneal physiology ‫‬
Opto Ihsan MH
 

Similar to Corneal transparency (20)

preeti cornea ..physiology of cornea.ppt
preeti cornea ..physiology of cornea.pptpreeti cornea ..physiology of cornea.ppt
preeti cornea ..physiology of cornea.ppt
 
preeti cornea , physiology of cornea....
preeti cornea , physiology of cornea....preeti cornea , physiology of cornea....
preeti cornea , physiology of cornea....
 
Physiology of cornea
Physiology of corneaPhysiology of cornea
Physiology of cornea
 
Physiology of cornea
Physiology of corneaPhysiology of cornea
Physiology of cornea
 
Cornea
Cornea Cornea
Cornea
 
CORNEA-Anatomy,Corneal Transperency.pptx
CORNEA-Anatomy,Corneal Transperency.pptxCORNEA-Anatomy,Corneal Transperency.pptx
CORNEA-Anatomy,Corneal Transperency.pptx
 
Anatomy of Cornea.pptx
Anatomy of Cornea.pptxAnatomy of Cornea.pptx
Anatomy of Cornea.pptx
 
Corneal transparency
Corneal transparency Corneal transparency
Corneal transparency
 
Cornea anatomy & physiology
Cornea  anatomy & physiologyCornea  anatomy & physiology
Cornea anatomy & physiology
 
1 Anatomy(Ant.segment-1) .pptx
1 Anatomy(Ant.segment-1)           .pptx1 Anatomy(Ant.segment-1)           .pptx
1 Anatomy(Ant.segment-1) .pptx
 
Anatomy of cornea
Anatomy of corneaAnatomy of cornea
Anatomy of cornea
 
conjunctiva.pptx
conjunctiva.pptxconjunctiva.pptx
conjunctiva.pptx
 
Corneal Physiology
Corneal PhysiologyCorneal Physiology
Corneal Physiology
 
Cornea anatomy simplified
Cornea anatomy simplifiedCornea anatomy simplified
Cornea anatomy simplified
 
Cornea
CorneaCornea
Cornea
 
Physiology of cornea
Physiology of corneaPhysiology of cornea
Physiology of cornea
 
Keratoplasty update 2016
Keratoplasty update 2016Keratoplasty update 2016
Keratoplasty update 2016
 
Corneal transparency
Corneal transparencyCorneal transparency
Corneal transparency
 
anatomy and physiology of cornea-.pdf gfhh
anatomy and physiology of cornea-.pdf gfhhanatomy and physiology of cornea-.pdf gfhh
anatomy and physiology of cornea-.pdf gfhh
 
Corneal physiology ‫‬
Corneal physiology ‫‬Corneal physiology ‫‬
Corneal physiology ‫‬
 

More from Hira Dahal

More from Hira Dahal (20)

Common binocular vision disorder neglected
Common binocular vision disorder neglectedCommon binocular vision disorder neglected
Common binocular vision disorder neglected
 
Gonioscopy presentation
Gonioscopy presentationGonioscopy presentation
Gonioscopy presentation
 
Glare testing and dark adaptation
Glare testing and dark adaptationGlare testing and dark adaptation
Glare testing and dark adaptation
 
Embryology and anatomy of human lens
Embryology and anatomy of human lensEmbryology and anatomy of human lens
Embryology and anatomy of human lens
 
Vitamins a
Vitamins aVitamins a
Vitamins a
 
Electrophysiology
ElectrophysiologyElectrophysiology
Electrophysiology
 
Anatomic and physiological ocular changes with age final
Anatomic and physiological ocular changes with age finalAnatomic and physiological ocular changes with age final
Anatomic and physiological ocular changes with age final
 
Visual field testing and interpretation
Visual field testing and interpretationVisual field testing and interpretation
Visual field testing and interpretation
 
Cyclorefraction
CyclorefractionCyclorefraction
Cyclorefraction
 
Colour vision examination
Colour vision examinationColour vision examination
Colour vision examination
 
Prisms in optometry practice
Prisms in optometry practicePrisms in optometry practice
Prisms in optometry practice
 
Therapeutic contact lens
Therapeutic contact lensTherapeutic contact lens
Therapeutic contact lens
 
Effects of radiation and glare in eye
Effects of radiation and glare in eyeEffects of radiation and glare in eye
Effects of radiation and glare in eye
 
Slit lamp biomicroscopy
Slit lamp biomicroscopySlit lamp biomicroscopy
Slit lamp biomicroscopy
 
General eye overview
General eye overviewGeneral eye overview
General eye overview
 
Frame slection
Frame slectionFrame slection
Frame slection
 
Circadian cycle
Circadian cycleCircadian cycle
Circadian cycle
 
RGP Complications
RGP ComplicationsRGP Complications
RGP Complications
 
Low vision rehabilitation
Low vision rehabilitationLow vision rehabilitation
Low vision rehabilitation
 
Retinoscopy
RetinoscopyRetinoscopy
Retinoscopy
 

Recently uploaded

Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose AcademicsCytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
MedicoseAcademics
 
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose AcademicsConnective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
MedicoseAcademics
 

Recently uploaded (20)

Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose AcademicsCytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
Cytoskeleton and Cell Inclusions - Dr Muhammad Ali Rabbani - Medicose Academics
 
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose AcademicsConnective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
Connective Tissue II - Dr Muhammad Ali Rabbani - Medicose Academics
 
Unlocking Holistic Wellness: Addressing Depression, Mental Well-Being, and St...
Unlocking Holistic Wellness: Addressing Depression, Mental Well-Being, and St...Unlocking Holistic Wellness: Addressing Depression, Mental Well-Being, and St...
Unlocking Holistic Wellness: Addressing Depression, Mental Well-Being, and St...
 
VIP Pune 7877925207 WhatsApp: Me All Time Serviℂe Available Day and Night
VIP Pune 7877925207 WhatsApp: Me All Time Serviℂe Available Day and NightVIP Pune 7877925207 WhatsApp: Me All Time Serviℂe Available Day and Night
VIP Pune 7877925207 WhatsApp: Me All Time Serviℂe Available Day and Night
 
Let's Talk About It: Ovarian Cancer (The Emotional Toll of Treatment Decision...
Let's Talk About It: Ovarian Cancer (The Emotional Toll of Treatment Decision...Let's Talk About It: Ovarian Cancer (The Emotional Toll of Treatment Decision...
Let's Talk About It: Ovarian Cancer (The Emotional Toll of Treatment Decision...
 
Video capsule endoscopy (VCE ) in children
Video capsule endoscopy (VCE ) in childrenVideo capsule endoscopy (VCE ) in children
Video capsule endoscopy (VCE ) in children
 
Mgr university bsc nursing adult health previous question paper with answers
Mgr university  bsc nursing adult health previous question paper with answersMgr university  bsc nursing adult health previous question paper with answers
Mgr university bsc nursing adult health previous question paper with answers
 
DR. Neha Mehta Best Psychologist.in India
DR. Neha Mehta Best Psychologist.in IndiaDR. Neha Mehta Best Psychologist.in India
DR. Neha Mehta Best Psychologist.in India
 
Treatment Choices for Slip Disc at Gokuldas Hospital
Treatment Choices for Slip Disc at Gokuldas HospitalTreatment Choices for Slip Disc at Gokuldas Hospital
Treatment Choices for Slip Disc at Gokuldas Hospital
 
Overview on the Automatic pill identifier
Overview on the Automatic pill identifierOverview on the Automatic pill identifier
Overview on the Automatic pill identifier
 
Sell pmk powder cas 28578-16-7 from pmk supplier Telegram +85297504341
Sell pmk powder cas 28578-16-7 from pmk supplier Telegram +85297504341Sell pmk powder cas 28578-16-7 from pmk supplier Telegram +85297504341
Sell pmk powder cas 28578-16-7 from pmk supplier Telegram +85297504341
 
ROSE CASE SPINAL SBRT BY DR KANHU CHARAN PATRO
ROSE  CASE SPINAL SBRT BY DR KANHU CHARAN PATROROSE  CASE SPINAL SBRT BY DR KANHU CHARAN PATRO
ROSE CASE SPINAL SBRT BY DR KANHU CHARAN PATRO
 
Renal Replacement Therapy in Acute Kidney Injury -time modality -Dr Ayman Se...
Renal Replacement Therapy in Acute Kidney Injury -time  modality -Dr Ayman Se...Renal Replacement Therapy in Acute Kidney Injury -time  modality -Dr Ayman Se...
Renal Replacement Therapy in Acute Kidney Injury -time modality -Dr Ayman Se...
 
Get the best psychology treatment in Indore at Gokuldas Hospital
Get the best psychology treatment in Indore at Gokuldas HospitalGet the best psychology treatment in Indore at Gokuldas Hospital
Get the best psychology treatment in Indore at Gokuldas Hospital
 
ANAPHYLAXIS BY DR.SOHAN BISWAS,MBBS,DNB(INTERNAL MEDICINE) RESIDENT.pptx
ANAPHYLAXIS BY DR.SOHAN BISWAS,MBBS,DNB(INTERNAL MEDICINE) RESIDENT.pptxANAPHYLAXIS BY DR.SOHAN BISWAS,MBBS,DNB(INTERNAL MEDICINE) RESIDENT.pptx
ANAPHYLAXIS BY DR.SOHAN BISWAS,MBBS,DNB(INTERNAL MEDICINE) RESIDENT.pptx
 
Quality control tests of suppository ...
Quality control tests  of suppository ...Quality control tests  of suppository ...
Quality control tests of suppository ...
 
Denture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of actionDenture base resins materials and its mechanism of action
Denture base resins materials and its mechanism of action
 
Making Patient-Centric Immunotherapy a Reality in Lung Cancer: Best Practices...
Making Patient-Centric Immunotherapy a Reality in Lung Cancer: Best Practices...Making Patient-Centric Immunotherapy a Reality in Lung Cancer: Best Practices...
Making Patient-Centric Immunotherapy a Reality in Lung Cancer: Best Practices...
 
Cas 28578-16-7 PMK ethyl glycidate ( new PMK powder) best suppler
Cas 28578-16-7 PMK ethyl glycidate ( new PMK powder) best supplerCas 28578-16-7 PMK ethyl glycidate ( new PMK powder) best suppler
Cas 28578-16-7 PMK ethyl glycidate ( new PMK powder) best suppler
 
HIFI* ℂall Girls In Thane West Phone 🔝 9920874524 🔝 💃 Me All Time Serviℂe Ava...
HIFI* ℂall Girls In Thane West Phone 🔝 9920874524 🔝 💃 Me All Time Serviℂe Ava...HIFI* ℂall Girls In Thane West Phone 🔝 9920874524 🔝 💃 Me All Time Serviℂe Ava...
HIFI* ℂall Girls In Thane West Phone 🔝 9920874524 🔝 💃 Me All Time Serviℂe Ava...
 

Corneal transparency

  • 2. Transparency is the quality or state of transmitting light without appreciable scattering so that bodies lying beyond are entirely visible . 2
  • 3. The cornea is an exquisite layered composite material with a structure ideally suited to its function as the transparent window in the tough outer tunic of the eye ball through which the outside world is viewed. 3
  • 4. The Cornea is a transparent avascular tissue with smooth outer convex surface and concave inner surface which resembles a small watch glass. Forms anterior one –sixth of the fibrous coat of the eye. 4
  • 5. Corneal Dimension Horizontal Vertical Anterior surface-- 11.7mm 10.6mm Posterior surface-11.7mm 11.7mm Radius of curvature Ant surface-7.8mm Post surface-6.5mm Corneal thickness Central-0.5-0.6mm Peripheral-1-1.2mm 5
  • 6. Functions of Cornea Optical : It forms the principal refractive surface accounting for some 70%(40-45 D) of total refractive power(60D). Barrier: Cornea provides a protective interference with the outer environment and also contain intraocular pressure. 6
  • 7. Layers of cornea Epithelium. Bowman layer. Lamellar Stroma. Descemet’s membrane. Endothelium. 7
  • 8. 1. Epithelium (50-90 um) 3 types of cell :- i) A single layer basal columnar cells stand as paliside like manner in perfect alignment on the basement membrane. Attached by hemidesmosomes to the epithelial basement membrane. ii)2- 3 rows of wing cells. iii) 2 layers of flattened surface cells - microplicae and microvilli - excellent ability to regenerate - attached by desmosomes , and zonulae occludens 8
  • 9. 9
  • 10. BIOCHEMICAL COMPOSITION OF EPITHELIUM Water (70% of wet weight) . Protein synthesis is 5 times higher than stroma. Lipid (Phospholipid and cholesterol). Enzymes. ATP,glycogen,glutathione,Ascorbic acid. Acetylecholine, cholinesterase. Electrolytes (K+,Na+,and Cl– ). 10
  • 11. 2. Bowman’s layer (8-14 um): Acellular mass of condensed collagen fibril. It is not true elastic membrane but simply continuation of stroma. Shows considerable resistance to infection and injury Does not regenerate. 11
  • 12. 3.3. Lamellar Stroma (0.5mm):(0.5mm): Consists collagen fibrils (lamellae) (200-250)and cells embedded in matrix (proteoglycans). Mean diameter of collagen fibril between 22.5&32nm,predominantly type I collagen.  Fibril within the lamellae are parallel to each other & also parallel to corneal plane Fibril within adjacent lamellae make various angles with respect to one other. 12
  • 13.  Stromal cells are keratocytes, wandering macrophages, histocytes etc.  Keratocytes are fibroblast which produce ground substance (keratin & chondrotin sulfate) and collagen fibril. The highly negatively charged keratin sulfate around collagen fibril maintain spatial relationship between them. 13
  • 14. BIOCHEMICAL COMPOSITION OF STROMA : -Water(78%) - Collagen (15%) - other protein (5%) - Glycosaminoglycan # Keratan sulfate(0.7%) # Chondroitin sulfate(0.3) # Chondroitin - Salts 14
  • 15. 4.4. Descemet’s membrane (3-40um):(3-40um): Homogeneous layer. Made up of collagen & glycoprotein. Resistant to chemical agent, trauma infection and pathological process . Can regenerate. 15
  • 16. 5.5. Endothelium :: -- Single layer polygonal cells - Attached to Descemet’s membrane by hemidesmosomes and laterally to each other by tight junctional complex . - barrier function is calcium dependent -Contains active pump mechanism -Involved in active secretion and protein synthesis 16
  • 17. 17 FACTORS AFFECTING CORNEAL TRANSPERANCY Anatomical factors: * Uniform & regular arrangement of corneal epithelium . * Peculiar arrangement of corneal stromal lamellae. * Corneal avascularity. Physiological factors: Relative state of corneal dehydration.
  • 19. 1. Corneal epithelium  Epithelial cells are closely packed.  Uniformity & regularity in arrangement.  Homogenicity in refractive index.  Tight intercellular junction. 19
  • 20. 2. Tear film  Keeps epithelial surface smooth.  Provides high quality optical surface. 20
  • 21. 3.3. Arrangement of stromal lamellae: Maurice Theory: Collagen fibrils of uniform diameter (275- 350Å)are packed regularly and thus creates a lattice pattern.  The fibril axis are located at the position of a perfect crystalline lattice.  Interfibrillar spacing is about 50-60nm and is smaller than wavelength of light (400-700nm).  Scattered light is destroyed by mutual or destructive interference 21
  • 22. Interference: Interference is the phenomenon by virtue of which there is a modification in the distribution of energy due to superimposition of two or more waves. ‘ Principle of superimposition’. This can be stated as: “ Whenever two or more sets of waves pass through and cross one another in the same medium, they behave independent of each other and net displacement of a particle , at any instant , is equal to the algebraic sum of the individual displacements due to all the waves.” 22
  • 23. Interference may be ‘constructive’ or ‘destructive’ In constructive interference the crest of one wave coincides with the crest of another and the net amplitude is equal to the sum of individual amplitudes. In destructive interference the crest of one wave coincides with the trough of another and the net amplitude is equal to the difference between the individual amplitudes. Scattered rays - destructive interference Rays on the line of incident light- Constructive interference 23 Destructive interference
  • 25. Findings contradictory to Maurice theory i) The cornea is not perfectly transparent, otherwise an ophthalmologist could not view cornea in the slit lamp.. ii) Shark’s cornea with regions of disorganised fibres and random distribution of interfibrillar distances is also quite transparent. . 25
  • 26. Hard core cylinder model of Twersky: Twersky proposed a model in which the fibrils had a composite structure consisting of an inner core, composed of collagen fibrils and outer coating of a material that matches the refractive index of the ground substance. The coating would increase correlations but not affect the light scattering properties of a fibril. The loss of transparency observed when the cornea swells would be explained in the hard core model on the basis of increased area available per fibril. 26
  • 27. Theory of Goldman & Benedek : Fibrils are small in relationship to wavelength of light and do not interfere with light transmission unless they are larger then one-half of a wavelength of light (2000Å). 27
  • 28. 4. Endotheliumis transparent because it is * Single layer. * Homogeneous. * Closely packed cells . * It has deturgescence function. 28
  • 29. 5. Corneal Vascularisation: Except for capillary palisade of limbus, normal cornea is avascular. Corneal avascularity factors are not known. When vessels present are due to corneal pathology. Vascularisation -Loss of transparency. 29
  • 30. Mechanical Theory : According to Cogan (1948)  Blood vessel can not invade normal cornea.  Loosening of compactness of corneal tissue due to oedema is a must for neovsacularisation. Interstitial keratitis where oedema always precedes vascularisation. Some vesostimulatory factor may be needed along with corneal oedema for neovascularisation to occur. 30
  • 31. Chemical theory: Role of vasoinhibitory factors(VIF) Sulfate ester of hyaluronic acidSulfate ester of hyaluronic acid Role of vasostimulatory factors (VSF) Low mol wt. AminesLow mol wt. Amines Corneal hypoxia→VSF stimulation→ Neovascularisation 31
  • 33. Corneal hydration : Normal cornea maintains itself in a state of relative dehydration (80% water content ) which is essential for corneal transparency. It is kept constant by--- 1) Factors which draw water in the cornea, like -Stromal swelling pressure (SP) -Intraocular pressure (IOP) 2 ) Factors which prevent flow of water in the cornea - Mechanical barrier function of epithelium & endothelium. 3) Factors which draw water out of cornea -active pumping action of endothelium. 33
  • 34. FACTORS AFFECTING CORNEAL HYDRATION: i) STROMAL SWELLING PRESSURE (SP, 60 mmHg): Pressure exerted by glycosaminoglycans(GAGs) of the corneal stroma which act like a sponge. Electrostatic repulsion of the anionic charges on the GAG molecule expands the tissue, sucking in the fluid with equal but negative pressure called, imbibition pressure (IP). 34
  • 35. In vitro, IP=SP In vivo, IP is reduced by values equivalent to IOP. i.e. IP=IOP- SP i.e. IP=17-60= - 43mmHg. Negative imbibation pressure draws out water from stroma. 35
  • 36. ii) Barrier function of epithelium and endothelium: Epithelium & endothelium are semipermiable in nature. Function as barriers to excessive flow of water and diffusion of electrolytes into the stroma. Epithelium offers most resistance to flow of water. 36
  • 37. iii) Hydration control by active pump mechanism: a) Na+ /K+ ATPase pump system: •Endothelium is more active than &epithelium, •Pumps are located in basolateral membrane of endothelial cell. •Stromal transparency develops 13-20 days after birth due to greatest increase in pump sites/cell. 37
  • 38. •Enzyme “Na+ /K+ activated ATPase” mediate pump causes extrusion of the Na+ & water from the stroma and thus maintain corneal transparency. •Corneal hydration depend on extent to which endothelial barrier and pump function can be reestablished. 38
  • 39. b) Bicarbonate dependent ATPase present in endothelium are also reported to have role in fluid /ion balance in the cornea. c) Carbonic enhydrase enzyme catalyzes the conversion of CO2and water into HCO3 - and H+ , thus provides important source for HCO3 - for endothelial pump. d) Na+ /H+ pump has also been postulated. 39
  • 40. 40
  • 41. Corneal thickness is increased and transparency is decreased when there is endothelial damage and to a lesser extend when epithelium is damaged. 41
  • 42. iv) Passive ion movement, like - K+ , Cl- and HCO3 - ions diffuse into aqueous humor. - Na+ , Cl- and HCO3 - diffusion in contra lateral direction. 42
  • 43. v) Hypoxia, pH and changes in the temperature can alter the metabolic activity of the cornea and thereby may cause alteration in corneal thickness and loss of transparency. 43
  • 44. vi) Intraocular pressure (IOP) : As we know , I P = IOP - SP, i.e. 17- 60= - 43 mmHg, i.e. I P is a negative pressure. When IOP exceeds SP, i.eWhen IOP exceeds SP, i.e. when I Pwhen I P becomes positive , corneal oedemabecomes positive , corneal oedema resul It can occur when there is - high IOP and normal SP,as in acute glaucoma, - Normal IOP and low SP, as in endothelial dystrophy. 44
  • 45. 45
  • 46. Corneal Swelling: Electron micrograph of a swollen cornea shows fibril distribution with region completely devoid of fibrils. These voids are called lakes, which have larger dimensions & spoils the interference that is critical to transparency. 46
  • 47. Photorefractive keratectomy using argon fluoride excimer laser: . Despite the excimer laser’s ability to ablate corneal tissue with good precision and with little collateral damage, the treatments commonly result in the development of increased subepithelial light scattering that gives the cornea a hazy appearance in the treated area. increased numbers of activated keratocytes and vacuoles within and around keratocytes adjacent to the treated area. Activated keratocytes may have different effective refractive indices than normal keratocytes, thus increasing their contribution to scattering. Vacuoles within and around keratocytes may act like the lakes seen in swollen cornea. 47
  • 48. vii) Evaporation of water from corneal surface: Evaporation of water from the pre-corneal tear film fluid → increase in osmolarity relative to cornea→hyper tonicity of tear film → flow of water from the cornea. 48
  • 49. Corneal transparency results from----- Interference among the residual waves scattered by different fibrils. The inefficiency of the fibrils as scatters. Avascularity of the cornea. The thinness of cornea which is maintained by a complex series of metabolically dependent reaction in the corneal endothelium and epithelium. 49