Q. What is the CORNEA?
A. This is a clear piece of tissue that fits like a watch crystal (outer glass cover of the watch) over the coloured part of the eye called the iris. Unlike the watch glass, which is flat, the cornea is dome shaped. Light passes through the transparent cornea, just like it would through a window, to the back of the eye. The parallel rays of light passing through the cornea gets bent so as to focus on the retina which is the inner lining of the back of the eye, like the film of the camera.
Q. How does the cornea get cloudy?
A. Clouding or irregularity of the cornea may be caused by many different kinds of problems. When the cornea becomes cloudy, similar to the frosting of glass, light is not able to pass through the eye and poor vision results. Some of the causes are:
· Infection and injury to the eye
· Nutritional disorders such as Vitamin A deficiency
· Reaction to drugs, e.g. Stevens–Johnson Syndrome
· Degenerations and dystrophies of the cornea (inherited conditions which may cause clouding of the cornea in adult life
· Keratoconus (an irregularity of the shape of the cornea, where there is progressive ‘coning’ of the cornea) In this condition even though the cornea is clear the quality of vision gradually deteriorates. Clouding only occurs in the very late stages.
· Corneal clouding as a complication of cataract or glaucoma surgery
Q. In such cases, how is vision restored?
A. The only way to restore vision is to replace the cornea with donated healthy corneal tissue 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 eye. The cornea is the only part of the eye that can be transplanted.
Q. How successful is cornea transplant surgery? Is it true that most corneal transplants become opaque in a few years?
A. The corneal transplant or corneal graft as it is also called, is devoid of blood vessels. Hence out of all transplants done in the body such as heart, liver, kidney etc, it has the least chance of rejection. I amend the previous statement – it would come second in terms of success rates to hair transplants! Even if rejection does occur, it can be successfully treated by eye drops in most cases without having to take recourse of systemic immunosuppressive medication, as is the case with rejected transplants elsewhere in the body. I have seen several grafts done 30 and 40 years ago, remaining crystal clear to this day! Grafts done in eyes where the cornea is already vascularised naturally, have a poorer long-term prognosis (expected outcome, in layman’s terms). However, in case a graft does fail or get rejected for some reason and the rejection is not reversed by timely treatment, all is not lost. If the rest of the eye has no other complications, it is possible to do a re graft i.e. one more graft (naturally after removing the previous opaque graft!) and restore vision once more.
Q. When does rejection usually occur?
A. Statistically speaking, rejection occurs most often in the first year after transplant and following any major or minor surgery to the eye there after i.e. a patient of corneal graft who now undergoes cataract surgery or even removal of his corneal sutures (commonly done a year or so after the corneal graft surgery) is at increased risk of graft rejection in the month immediately following the surgical procedure.
Q. How does the patient know that there is early rejection and he should rush to the nearest eye doctor?
A. If the patient suddenly experiences increase in redness, pain, watering of the operated eye or a drop in vision in the same eye, he should immediately see his nearest eye doctor, preferably on the same day. He should avoid the temptation of taking telephonic advice for his symptoms. This is because these same symptoms can occur in graft rejection as well as in graft infection. The treatment for the former is very frequent instillation of topical corticosteroid drops while this will make the condition worse if it is a graft infection and not a rejection.
Q. Can all opaque corneas be successfully transplanted to restore vision?
A. I did mention a few paragraphs ago that those corneas already having blood vessels growing into them have a poorer prognosis (Meaning of Prognosis also explained in a previous answer). Besides these, eyes which have a history of previous grafts rejected are more at risk to develop rejection again as the body now knows that there is an intruder and sends its defence forces (white blood ‘killer’ cells) to destroy the invader! Besides, eyes with an inadequate tear secretion or with poor quality tears are not good candidates for corneal grafting. Any condition that has destroyed the “limbus” i.e. the factory that constantly replenishes the cells on the surface of the cornea, which is situated at the junction between the black and the white of the eye, makes a corneal transplant surgery doomed to failure. Some of these conditions are chemical burn injuries, drug reactions such as Stevens Johnson syndrome, which destroy the stem cells at the limbus and certain congenital conditions such as Aniridia, in which there is a very poor quota of stem cells to begin with. For more information on stem cells, read the chapter on “Ocular Surface disorders”.
Q. What is the ‘new’ development in cornea transplant surgery – the ‘lamellar’ corneal transplant or keratoplasty?
A. Most corneal transplants done in India and even the world over are ‘full thickness’ corneal transplants (technically called penetrating keratoplasty). 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 conical cornea or in superficial corneal scars, the innermost lining of the cornea, called the endothelium is intact and healthy and therefore need not be changed. In these cases, approximately 90% of the thickness is changed, i.e. the innermost layer, the endothelium is left unchanged. Since it is the donor endothelium which is chiefly responsible for the rejection response by the patient’s immune system, the chances of rejection of this ‘lamellar’ graft are reduced dramatically. However, this procedure requires a little more skill than the usual penetrating keratoplasty and has a rate of operative complications (necessitating conversion to penetrating keratoplasty) of about 5-10% in the best of hands. Also, DALK (deep anterior lamellar keratoplasty as it is also called) cannot be used in patients who have unhealthy endothelium. It therefore requires careful patient selection.
Q. I have heard of another procedure called “Endothelial Keratoplasty”. What is this?
A. I congratulate you for your hearing abilities. This procedure, which is even more technically demanding than DALK, requires special instruments and is still not routinely done. This is transplantation of only the inner lining of the cornea – the endothelium, after stripping off the patient’s own inner lining. It is also known as DSEK and DSAEK and posterior lamellar keratoplasty. You need not bother your head with the full forms of these acronyms. You probably will forget them after reading them anyway. It can be done for those whose corneal inner lining only is dysfunctional and the rest of the cornea is OK. Sutures are generally not required in such cases, so visual recovery is much faster and suture related complications are eliminated.
Q. Is there any hope of restoring vision for those unfortunate patients who cannot have or will not benefit from a cornea transplant but have a diseased cornea?
A. Yes, they can be fitted with an artificial cornea or Keratoprosthesis, for which you are advised to read the chapter especially devoted to the subject.
Q. What are the expenses involved in corneal transplantation?
A. These vary considerably depending on the geographical region of the country you get the surgery done. In many places inIndia, these surgeries are done only in government, municipal or trust hospitals where there is no charge or a minimal cost. In the larger cities, it is done in the private sector as well. Though the eyeball is donated free of cost, most eye banks run extensive tests on the donated tissue as well as test the blood of the donor for AIDS, Hepatitis and other communicable diseases. They also employ highly qualified staff that evaluates the eyeball to decide suitability of its use. All this costs money, which is levied by the eye bank as “processing charges”. In Mumbai for example, this cost is around Rs.6000/-per patient at the time of writing this edition. This charge is only levied upon patients in the private sector, which forms only 30% of all patients receiving donated corneas in Mumbai. The remaining 70% of cornea is distributed practically free of cost to the municipal and free hospitals of Mumbai.
Q. What about surgical fees?
A. These also vary from state to state. In states where there is private sector corneal grafting surgeries performed, the professional fees charged by an eye surgeon is usually around what he would charge for modern day cataract surgery.
Q. Is this morally justified? After all he is receiving a donated eyeball free from the deceased donor!
A. Morality is a relative issue. No surgeon charges for the eyeball or cornea (eye banks may however charge a processing fee – refer to previous answer). However, surgeons trained in corneal grafting surgery have spent a lot of money to acquire this expertise. Also, they do need good surgical microscopes, disposable trephines and other costly tools to do good corneal grafting surgery. Most corneal surgeons would like to do only corneal surgery to earn their livelihood. However as tissue availability is low, they end up doing cataract and other surgeries as well to earn their daily bread. Practically no eye surgeon in the private sector survives on the income from corneal transplant surgery alone. Most eye surgeons who do a fair number of transplants use the income from affording patients to subsidise the surgery for those that cannot afford.
Q. Can every blind person have his sight restored by an “eye transplant”?
A. No, corneal grafting or corneal transplant surgery can only benefit those who are blind due to the cornea becoming opaque. The rest of the tissues of the eye cannot be transplanted. As of today, retinal transplants are being tried on an experimental basis but it will be many years if at all, before this procedure can be done successfully to restore vision to those having diseased retinas.
Q. Can a person who has received a corneal transplant himself donate his cornea after death?
A. Yes. If the cornea is clear, it can be re-used to give sight to one more corneally blind person. It would be a truly noble gesture!