The cornea is the clear, dome-shaped, round structure we see in front of the eyes. It is responsible for about two thirds of the eye’s focusing power. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor inside the eye. The cornea is a transparent structure and to see well all layers of the cornea must be free of any opacities. When the cornea becomes cloudy due to disease, injury, infection or malnutrition, vision is significantly lost or reduced.
Treating corneal blindness is possible through cornea transplant. In this treatment, a healthy cornea is transplanted in place of a diseased cornea called as penetrating keratoplasty. Sometimes part of the cornea is transplanted called as lamellar keratoplasty.
Of all tissue transplants, corneal transplants are the most successful. A cornea transplant is done in the following circumstances:
Cornea graft rejection though rare, may occur after surgery; when this might occur cannot be predicted. Rejection can be successfully reversed, and vision regained if prompt medical therapy is given.
Most corneal transplants are ‘full thickness’ corneal transplants. 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 lining of the cornea, called the endothelium is intact and healthy and is not changed. This procedure is called Deep Anterior Lamellar Keratoplasty (DALK). As compared to a full thickness graft, it offers a faster rehabilitation and reduced rate of rejection with improved graft survival.
Newer techniques of corneal transplant are endothelial keratoplasty (DSAEK / DMEK). In this only the endothelial layer of the cornea is replaced, allowing surgeon to target the specific cause of the patient’s vision loss. No sutures are placed and hence recovery is faster. As it is very comfortable it is the procedure of choice in cases of Fuchs dystrophy and corneal decompensation.
A fleshy overgrowth of tissue may occur over the cornea and this may lead to astigmatism or obstruct the vision. This can be successfully removed by surgery and recurrence prevented by an autograft. This is better operated upon early to avoid permanent damage to the vision.
Keratoconus is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape. This cone shape deflects light as it enters the eye on its way to the light-sensitive retina, causing distorted vision.
As the cornea becomes more irregular in shape, it causes progressive nearsightedness and irregular astigmatism, creating additional problems with distorted and blurred vision. Glare and light sensitivity also may occur.
In the mildest form of keratoconus, eyeglasses or soft contact lenses may help. But as the disease progresses and the cornea thins and becomes increasingly irregular in shape, glasses and regular soft contact lens designs no longer provide adequate vision correction.
Treatments for progressive keratoconus include corneal cross-linking (CXL) in which riboflavin is applied to strengthen the cornea by increasing the number of anchors that bond the corneal collaged fibers together. Other options include custom soft contact lenses, gas permeable contact lenses, scleral lenses, prosthetic contact lenses, topography guided conductive keratoplasty and if needed even a corneal transplant.