Corneal Transplantation

Customized Component Corneal Transplantation

Corneal transplantation is a surgical procedure aimed at providing eye sight to people suffering from corneal blindness. Corneal blindness accounts for almost 15% of the blindness in our country. The important issue here is that this blindness is preventable. Corneal transplantation can help rehabilitate these people provided adequate corneas are available. Cornea is the clear, transparent part in front of the eye much like the watch-glass of a wrist watch. It is responsible for 2/3rd of the refracting power of the eye.
The cornea has 5 layers:
1) Epithelium- Is a layer of cells that covers the surface of the cornea. It is about 5-6 cell layers thick and quickly regenerates when the cornea is injured.
2) Boman’s membrane- lies just beneath the epithelium. It is a relatively tougher layer and protects the cornea from injury.
3) The stroma is the thickest layer and lies just beneath Bowman’s membrane. It is composed of tiny collagen (a type of protein) fibrils that run parallel to each other. This special formation of the collagen fibrils gives the cornea its clarity.
4) Descemet’s membrane lies between the stroma and the endothelium. This layer serves as a scaffold for the endothelial cells.
5) Endothelium- Is a one cell layer thick. This layer pumps out water from the cornea, keeping it clear. If damaged or disease, these cells will not regenerate and cornea will lose its clarity.
Any opacification in the form of scarring of the cornea or fluid accumulation will impede the light from going inside the eye onto the retina (similar to the film of a camera) and thereby lead to diminution of vision.Corneal blindness can be due to various causes. Some of them are:
1) Malnutrition- Vitamin A deficiency is a common cause in children.
2) Scarring subsequent to bacterial, fungal or viral infections.
3) Eye trauma- Crackers during Diwali and Bow & Arrow injuries during Dusshera.
4) Hereditary diseases- Dystrophies
5) Degenerative conditions- Spheroidal degeneration, Band shaped keratopathy

An idea of the magnitude of the problem can be obtained by some statistics. There are 1.1 million corneally blind people in India, but only 12,927 could get a cornea transplant in 2006. In Delhi there are approximately 70,000 recorded deaths every year. However, less than a 1000 eye donations take place.

Superstitions against organ or eye donation and lack of awareness contribute to this scarcity of the cornea.

In this scenario the ability to use one cornea for multiple patients was always a very desirable solution, especially so because most patients need only a part of the cornea.

We now have the ability to use different parts of a cornea for different patients. As a result one cornea can be used for 3 patients. This is known as “Customized Component Corneal Transplantation”.

Corneal diseases often affect only a part of the disease. As a result the specific diseased part of the cornea is replaced by a corresponding healthy part from the donor cornea.

Some of the diseases that can benefit from selective transplantation of corneal layers are:-
1) Diseases benefiting from transplantation of front part of the cornea- Macular Dystrophy, Lattice dystrophy, Granular dystrophy, Keratoconus, Spheroidal degeneration
2) Diseases benefiting from transplantation of rear part of the cornea- Fuch’s dystrophy, Pseudophakic and aphakic bullous keratopathy
3) Diseases benefiting from limbal stem cell transplantation- Limbus is the outer, peripheral rim of the cornea. It has cells which grow inwards and contribute to the outer protective layer of the cornea called the epithelium. In conditions with limbal stem cell deficiency, like chemical injuries, Stevens-Johnson syndrome and ocular cicatricial pemphigoid, the peripheral region of a healthy donor cornea containing theses cells is transplanted on to the recipient.

A donor cornea is divided into 3 parts using a microkeratome (a special device that can accurately cut thin slices of cornea measuring in microns) and a trephine (a sharp circular blade).

The front part of the donor cornea is transplanted into patients with diseases involving primarily the front part of the cornea. This procedure is called “Anterior Lamellar Keratoplasty”.

Similarly, the rear part of the donor cornea is transplanted into patients with a pathology of the rear part of the cornea. This procedure is called “Posterior Lamellar Keratoplasty” with its latest variant being “Descemet’s Stripping Automated Endothelial Keratoplasty” (DSAEK). In DSAEK, a thin layer of the rear part of cornea comprising of Endothelium, Descemet’s membrane and a very thin layer of Stroma is utilized for transplanting.

The peripheral part of the donor cornea is used for Limbal Stem Cell Transplantation in patients suffering from limbal stem cell deficiency.

Customized Component Corneal Transplantation offers many advantages over conventional cornea transplantation. It reduces the risk of graft rejection (a major cause of transplant failure), reduces surgical trauma and potentially yields better refractive results. It also allows enables us to utilize one donor cornea in more than one patient.

In our country with a chronic shortage of donor corneas, this cornea-splitting technique appears very exciting because the scarcity of cornea will come down three-folds.
However, every endeavour should be made to increase eye donations so that more and more people can benefit from these simple vision restoring procedures.

Dr Ashu Agarwal, 29th August, 2007

Cataract Surgery