Lect.cornea

“CORNEA”
• PREPARED BY
YUMNA TARIQ
M.Phil. Scholar

CONTENTS:
 Introduction
 Corneal Dimensions
 Histology
 Blood supply/ Nerve supply
 Physiology
 MCQ’s

What is cornea?
 Origin:
From Latin cornea tela (“horny tissue”)
Cornu = (“horn”)
Tela = tissue

“Cornea is a Transparent,Avascular tissue with a
smooth, convex outer surface and concave inner surface,
which resembles a small watch glass”
 Forms 1/6th of the Eyeball
 The remaining 5/6th is formed by sclera

DIMENSIONS:
ANTERIOR SURFACE:
1. Elliptical & Convex in shape
2.Vertical Diameter = 10.6mm
3. Horizontal Diameter = 11.7mm
b. Posterior Surface:
1. Circular, Concave Shape
2. both horizontal and vertical diameter = 11.7mm

 Thickness:
- Centrally about 0.5 to 0.6mm
- peripherally about 0.7mm
 Radius of Curvature:
- ant. surface = 7.7mm
- post. Surface = 6.9mm
 Optical Zone:
- central 1/3rd area
- 5.4mm
 Refractive Power:
+43.1 D
 Refractive Index: 1.376

 Shape of cornea is important for fitting contact
lenses
 For some pathological conditions corneal
thickness is important
 Curvature varies from apex to limbus
 Corneal flattening is extensive at nasal than
temporal cornea
 This is Resembles a Prolate surface.

Microscopic structure of the cornea:
Behind the pre-corneal tearfilm there are 5 layers of
cornea:
1. Anterior Epithelium
2. Bowman’s Layer
3.Corneal stroma
4.Descemets’s membrane
5. Endothelium

1.Epithelium:
 Stratified
 Non-keratinized
 Squamous
 Thickness= 50-60micrometer
 5- layers of cells
 1. the superficial cells
 2. the Wing cells
 3. Basal cells
 Complete turn over of corneal epithelium takes place every 7 days.
 Source of stem cells= limbal basal cells
 Movement of the cells occur from the periphery to the center of
cornea
 Palisade of Vogt……. Radial folds of Epithelium

a. The superficial cell layer:
 Two to three cells thick
 Flat
 Horizontal nuclei
 Attached to one another by Desmosomes
 Have microvilli and microplicae
 When they age, they lose there
attachment to one another and are lost in
tear film
Function: tearfilm stability

b. Wing Cells:
 1-2 epithelial cell layers
 Wing shape
 Oval or round nuclei
 Each cell is polyhedral in shape
- anterior surface= convex
- posterior surface = concave
 Attach to one another by desmosomes
 Numerous gap junctions for free intercellular
communication

c. The basel layer:
 Single layer
 Tall, columnar cells
 Cells are attach to one another by
desmosomes
 Have gap junctions
 Cells are attach with a resting membrane or
basemant membrane by Hemidesmosomes

2. Bowman’s Layer:
 Lie beneath the basement membrane of corneal
epithelium
 Thickness = 8-12 micro meter
 Acellular and consist of Collagen fibrils
 Not a basement membrane
 No Regeneration Power
 Scar formation after Injury

3. Corneal Stroma:
 Thickness = 500 micron
 90% of the total thickness of the Cornea
 Transparent and fibrous
 Consist of:
a. Keratocytes:
- corneal fibroblast cells
- present through out Stroma
- these cells produces Extra Cellular Matrix
b. Extra cellular Matrix
- produce by keratocytes
- made up of glyco-proteins, which are water soluble and collagen
lamellae ( mainly type III and type vI), arranged parallel with cor.surface
- has a core protein & Anionic Polysaccharide Side Chain called
GAG( Glycosaminoglycan)

Core Proteins:
- 4 proteins in Cornea
1. Decorin
2. Lumican
3. Keratocan
4. Mimecan
GAGs:
- 2 side chains
1. keratin Sulfate (60%)
2. Dermatan Sulfate (40%)

4. Descemets Membrane:
• Posterior to stroma
• Acellular
• Its basement membrane of endothelium
• 10 micron thick in adults
• Collagen fibrils type IV
• Tough and elastic
• Has regenerative property

5. Endothelium:
 Single layer
 Hexagonal , flattened cells
 Non- Collagenous
 Numerous mitochondria, ER, Golgiapparatus
 Posterior surface has microvilli
 Tight junctions, hemi desmosomes
 No regeneration
 Control normal Hydration of cornea by two processes:
1. Barrier function
2. Active transport Mechanism

Blood supply: avascular
Lymphatic drainage: No any
Nerve Supply:
Opthalmic division of Trigeminal
Nerve through Long Cil.Nerve

Physiology:
1. Transmission of Light
2. Refraction of light
3. Structural integrity of eyeball
4. Protection of eyeball

1. Cornea ?
a. vascular
b. forms 5/6th of the eyeball anteriorly
c. Flattening is symmetrical in periphery
d. Non of the above

2. Endothelium:
a. Surface cells
b. Keratocytes
c. Wing cells
d. Hexagonal cells

3.cornealLayers?
a. 1
b. 7
c. 8
d. 5

Lect.cornea

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