Cornea is the transparent part of the eye that fits like watch glass over the coloured part of the eye called iris. Light passes through the clear transparent cornea to finally fall over retina.

There are six layers in the cornea:

1) Epithelium: It is the outermost layer of about 6 layers of cells. It has strong regenerative capacity, if limbal stem cells are intact.
2) Bowman’s Membrane: It is a tough acellular layer, mainly composed of collagen.
3) Stroma: about 90% of thickness of cornea is comprised of stroma. Stroma consists of regularly arranged collagen fibers intermixed with keratocytes.
4) Dua’s layer: This layer has been recently discovered by Dr Dua. It is very thin (5 to 20 micron thick) layer
5) Descemet’s membrane: It is the thin acellular layer made of Type-IV collagen mainly. Descemets layer serves as the purpose of basement membrane of endothelium.
6) Endothelium: It is the innermost layer of cornea made of single layer of cells and is about 5 micron thick. Unlike corneal epithelium, the endothelial cells do not regenerate. Instead they stretch to compensate for dead cells which reduce the density of these cells. Endothelium is responsible for maintaining fluid and solute transport between stroma and aqueous. If diseased endothelium is not able to maintain fluid balance, stromal swelling occurs and cornea loses its transparency.

Clouding or irregularity of the cornea may be caused by many different kinds of problems. Some of the causes are:

Hazy cornea due to Corneal Decompensation

When the cornea becomes hazy, similar to the frosting of glass, light is not able to pass through the eye resulting in poor vision.

The only way to restore vision is to replace the cornea with donated healthy corneal tissue

Corneal Transplant

by a surgery called corneal transplant or keratoplasty. This consists of removal of a central disc of the abnormal cornea and replacing it with a similarly sized piece of normal cornea obtained from a donor’s eye.

It is a misconception that the whole eye can be transplanted. The cornea is the only part of the eye that can be transplanted.

Acute-Rejection-after-Corneal-Transplant

Rejection is the immunological destruction of the cornea. Rejection is usually acute and many times it can be reversed with intensive therapy. The term “graft rejection” refers to the specific immunologic response of the host to the donor cornea. Because it is a specific process, it should be distinguished from other causes of “graft failure” that are not immune-mediated

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Signs of rejection can be remembered as an acronym: R.S.V.P.
R: Redness
S: Sensitivity to light
V: Vision loss
P: Pain

If the patient suddenly experiences an increase in redness, pain, watering of the operated eye, or a drop in vision in the same eye, he/ she should immediately consult the nearest cornea surgeon, preferably on the same day. Early graft rejection and early graft infection both can present similarly, but the treatment for both is exactly the opposite.

No. Corneal transplant can cure only “Corneal blindness”.

In case of penetrating keratoplasty (PK), the diseased cornea is removed with all its layers and replaced by a similar or slightly larger sized donor cornea also of ‘full’ thickness. However in certain diseases such as Keratoconus or in superficial corneal scars, the innermost layer of the cornea (endothelium) is intact and healthy and therefore need not be changed. In these cases, approximately 90% of the thickness is changed, i.e. the endothelium is left intact. Since it is the donor endothelium which is mainly responsible for the rejection, the chances of rejection of this ‘lamellar’ graft are reduced dramatically. However, this procedure requires a more surgical skill than the usual penetrating keratoplasty. It cannot be used in patients who have unhealthy endothelium. It therefore requires careful patient selection.

In some cases, only the innermost layer of cornea (endothelium) is diseased / non-functional. Endothelium is responsible for keeping the cornea clear. Endothelium can be compromised in post-cataract surgery cases or some inherited diseases like Fuch’s Dystrophy or ICE Syndrome. DSEK is partial thickness corneal transplants which replace primarily the endothelium (innermost portion of the cornea) rather than the full thickness of the cornea. To be specific, in DSEK, Endothelium, Descemet’s membrane and some part of stroma is transplanted.

In DMEK, only Endothelium along with Descemet’s membrane is transplanted. DMEK is the most physiological endothelial transplant.