Anatomy of cornea of dr. sohel mahmud

ANATOMY OF THE CORNEA

Presentation is made by

Dr. Sohel MahmudMBBS, DO.

Eye specialist & Surgeon,

Dhaka, Bangladesh.

IntroductionWe obtain more than 80% of our information from the external

world by means of visual function.

It is the transparent, avascular, watchglass-like

structure of anterior outer coat of eyeball.

Cornea serves as the gateway of light into the

eye.

Ancient Greek

used to believe

that cornea is

derived from

thinly sliced

horn of animal.

‘‘Kerato’’ in

Greek means

horn or shield

like.Medical terms

related to the

cornea often

start with the

prefix "kerat-"

The word Cornea comes

from “Kerato”.

Corneal epithelium-

From surface ectoderm

Descemet’s mem and

endothelium-

mesenchymal cells from

margin of optic cup

Bowman’s layer and

stroma- mesenchymal

cells insinuteate between

surface ectoderm and

developing lens

Cornea

Corneal development

1.Cornea forms anterior one-sixth of the outer coat of eye

ball.

Gross feature of cornea

Gross feature cont…

2. Anterior surface is elliptical with a horizontal diameter

of

11.7mm and vertical diameter of 10.6mm.

3. Posterior surface is circular with an average diameter of

11.7mm.

HD=11.7mm

VD=10.6mm

Anterior aspect Posterior aspect

AD=11.7mm

Gross feature cont…

4. Thickness in the center is 0.52mm while at the periphery

is 0.67mm.

5. The radius of curvature of anterior surface is 7.8mm and

posterior surface 6.5mm.

Thickness of the cornea

7.8mm

6.5mm

Radius of curvature of the cornea

Gross feature cont…

6. Refractive power of the anterior surface is +48.8 D

and of its posterior surface is —5.8 D.

So, net refractive power is +43 D.

7. Refractive index is 1.376.

Gross feature cont…

Histology Cornea consist of 5

distinct layers (from

anterior to posterior)–

1. Epithelium

2. Bowman’s membrane

3. Stroma

4. Descemet’s membrane

5. Endothelium

Epithelium

Represents 10 percent of the

corneal thickness.

About 50-90µm thick and

consist of 5-6 layers of cells.

It is stratified squamous

nonkeratinised epithelium.

Divided into -

• Superficial squamous cells layer

• Middle wing cells layer

• Inner basal cells layer

Epithelium cont…

Basal layer

Comprises tall columnar

polygonal shaped cells

arranged in a palisade

like manner on

basement membrane.

Attached to the

basement membrane

with hemidesmosomes

and each-other with

desmosomes.

Capable of mitosis.

Epithelium cont…

Flatten cells layer

2 most superficial layers

Long thin cells with

flatten nuclei.

Most superficial cells

have microvilli.

Wing cells layer

2-3 layers of pollyhedral

cells

Flatten and parallel nuclei

Corneal epithelial surface

showing microvilli and

mcroplicae

Corneal epithelium

Bowman's Layer

( Thickness 8-14 µm –

composed of randomly

arranged collagen fibers

)

Named after English anatomist and

ophthalmologist Sir William

Bowman.

Acellular tough membrane like zone.

Condensed superficial part of stroma.

It is not a basement membrane.

Once destroyed it cannot be

regenerated.

Composed of

collagen fibrils,

keratocytes and

extracellular ground

substances.

Collagen

components

constitute more than

70% of the dry

weight of cornea.

Stroma

90% of total

corneal

thickness

stroma

Collagen fibrils with uniform 25- to

35-nm diameter - arranged in flat

bundles called lamellae.

Distance between two fibers is also

highly uniform (41.5nm)

Collagen fibers form approximately

300 lamellae in corneal stroma.

Collagen fibrils

Types of collagen fibers present in the different layers of the cornea

Extracellular matrix or ground

substances found - mainly

glycosaminoglycan.

Primary glycosaminoglycans of

the stroma

- Keratin sulfate (65%) and

- Chondroitin sulfate.

Ground substances

Occupy 3-5% of the stromal volume.

Flattened cell body, eccentric nucleus and

long branching processes.

Found scattered in between the lamellae of

collagen fibers.

Synthesize collagen and extracellular

matrix

components.

Keratocytes(corneal fibroblasts ---major

cell type of the stroma)

Cellular component

Descemet's Membrane

Named after French physician Jean

Descemet (1732–1810).

Thick basement membrane secreted by

the endothelium.

Produced constantly - thickens

throughout life (5µm at birth /10-12

µm in adult).

No elastic fibers present – Though

exhibit elastic property due to the

particular arrangement of collagen

fibers.

Descemet’s

membrane

Descemet's Membrane cont. Terminates near limbus as

Schwalbe’s line.

On electronmicroscope- divided 2

distinct zone.

Once destroyed - can regenerated.

Tough layer - resistant to enzymatic

degradation by phagocytes and

toxins.

Does not adhere strongly to the

stroma - surgically dissected as a

sheet.

Descemet’s

membrane

Single layer, hexagonal, cuboidal

cells.

Mosaic pattern- best seen in

specular microscopy.

Possess ion transport system -

known as endothelial pump.

Cannot divide or replicate.

Endothelium

Corneal endothelium

Corneal endothelium cont..

Interconnected with each other with various

junctional complexes .

With ageing, the cell density of the endothelium

decreases.

6000

Aging Changes in the corneal layers

With advancing age- Cornea becomes less translucent and dust like

due to condensation of stroma.

Bowman’s and Descemet’s membrane are also thickened.

Arcus senilis appear.

Hassall Henle bodies are found periphery of the

descemet’s membrane.

Blood supply

Cornea is avascular and devoid of

lymphatic

drainage.

It is nourished by diffusion from aqueous

and capillaries at it’s edge.

Nasociliary nerve branch of ophthalmic division of trigeminal

nerve

Long ciliary nerves enter the eyeball around optic nerve

Runs anteriorly in suprachoroida space, a short distance from

limbus, they pierce the sclera

Divides dichotomously, connect with each other & with

conjunctival nerves to form pericorneal plexus of nerves

Nerve supply

After going 1-2mm in the stroma corneal nerves loss their myalin

sheath covering and devided dichotomusly and form 3 nerve

network.

60-80 mylinated trunks from pericorneal plexus enter the cornea

1. Stromal plexus (in mid stroma)

2. Sub epithelial plexus

(located in between Bowman’s layer and anterior stroma)

3. Intra epithelial plexus

Nerve fibers terminate as naked nerve endings between tightly

packed epithelial cells.

Nerve passes anteriorly and

form

Nerve passes Bowman’s layer and

form

Nerve supply

Pericorneal plexus

Stromal plexus

Subepithelial

plexus

Intra epithelial plexus

LCN

Corneal layers in Slit section

Slit section of normal

cornea-

1. Tear film

2. Epithelium

3. Anterior stroma

4. Posterior stroma

5. Descemet’s

membrane and

endothelium

Corneal layers in Confocal biomicroscope

Superficial layer of corneal

epithelium

Basal cell layer of corneal

epithelium

Sub epithelial nerve plexus Shallow layer of stroma

containing polygonal

keratocytes and straight-

branching nerve fibers

Deep layer of stroma

containing keratocytes and

stout nonbranching nerve

fibers

Endothelium- hexagonal

and uniform size

Applied anatomy

Knowledge of anatomy of cornea and it’s layers is

important for diagnosis and management of many

diseases and as well as for many surgical techniques.

Such as-

1. Penetrating Keratoplasty

2. Superficial lamellar keratoplasty

3. Deep anterior lamellar keratoplasty(DALK)4. Descemet striping endothelial keratoplasty(DESK)

5. Photorefractive keratectomy(PRK)

6. LASEK

7. LASIK

THANK YOU