LAYERS OF CORNEA&

THEIR FUNCTIONS- Solanki Riddhi (B.Optom.) Roll no : 05

CORNEAProvides greatest amount of refractive power to the eye.Elliptical in shape.Has 5 layers.1. EPITHELIUM2. BOWMAN’S LAYER3. STROMA4. DESCEMET’S MEMBRANE5. ENDOTHELIUM

CORNEA

1. EPITHELIUM Outermost layer of the cornea. Smooth corneal surface. Cells regenerate (only layer of the

cornea that does this) Made up of epithelial tissue. Cells of deepest layers are

columnar, known as basal cells. Middle layer cells are polyhedral

cells called wing cells.

Lastly , there are three or four layers of squamous cells, with flattened nuclei.

FUNCTIONS OF EPITHELIUM

Acts as a barrier to protect the cornea. Resisting the free flow of fluids from the

tears. Prevents bacteria from entering the

epithelium & corneal stroma.

EPITHELIUM

2. BOWMAN’S LAYER Second layer of the cornea. Is made up of a dense fibrous

sheet of collagen fibers. A transition layer between the

epithelium and stroma. Does not regenerate. Composed of strong, randomly

oriented collagen fibrils .

FUNCTIONS OF BOWMAN’S LAYER

Act as a physical barrier to protect the subepithelial nerve plexus.

Serve as a barrier that prevents direct traumatic contact with the corneal stroma & hence it is highly involved in stromal healing.

Associated with the corneal transparency at the morphological level.

BOWMAN’S LAYER

3. STROMA

Accounts for 90% of total thickness (largest layer)

Fibers in this layer contribute to corneal transparency.

Composed of about 200 flattened lamellae.

FUNCTIONS OF STROMA

Secrete an extracellular matrix, which includes collagen and proteoglycans.

And also produce crystalline proteins to maintain corneal transparency

STROMA

4. DESCEMET’S MEMBRANE Considered basement membrane to

the Endothelium. Produces constantly, which means it

thickens over one’s lifetime (will approximately triple in thickness over the course of your life)

 It is composed of a different kind of collagen (Type VIII) than the stroma.

The endothelial layer is located at the posterior of the cornea.

FUNCTIONS OF DESCEMET’S MEMBRANE

This layer is important for the health of endothelial cells.

One of the leading needs for cornea transplant is from a dystrophy of Descemet’s layer called Fuch’s dystrophy.

DESCEMET’S MEMBRANE

5. ENDOTHELIUM Innermost layer of cornea. Composed of one single layer of

cells. Cells do not divide or replicate. Separates the cornea from the

anterior portion of the eye. The corneal endothelium are

specialized, flattened, mitochondria-rich cells that line the posterior surface of the cornea and face anterior chamber of the eye.

FUNCTIONS OF ENDOTHELIUM

Governs fluid and solute transport across the posterior surface of the cornea.

Actively maintains the cornea in the slightly dehydrated state that is required for optical transparency.

ENDOTHELIUM

DUA’S LAYER Dua’s layer, according to a 2013 paper by Harminder Singh

Dua’s group at the University of Nottingham, is a layer of the cornea that had not been detected previously.

It is hypothetically  0.00059 inches thick, the fourth caudal layer, and located between the corneal stroma and Descemet’s membrane.

Despite its thinness, the layer is very strong and impervious to air. It is strong enough to withstand up to 2 bars (200 kPa) of pressure.

While some scientists welcomed the announcement, other scientists cautioned that time was needed for other researchers to confirm the discovery and its significance. Others have met the claim "with incredulity". The choice of the name Dua’s layer has also been criticized.

DUA’S LAYER

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