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 get 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 regraft 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 thereafter 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.