The cornea is the clear tissue covering the front of the eye and, if it becomes abnormal due to disease or damage, a corneal transplant may be necessary. Keratoplasty surgery is carried out, in which corneal tissue from a donor is used to replace unhealthy areas of the patient's cornea. Different methods of keratoplasty surgery may be employed depending on the type of condition the patient has. Options include a penetrating keratoplasty, where the whole cornea is replaced, and an endothelial keratoplasty, which replaces the cornea's inner lining. In a conductive keratoplasty, no transplant takes place, but surgery is used to alter the cornea's shape to correct problems such as farsightedness.
Penetrating keratoplasty surgery may be required when the cornea is damaged and scarred, causing its shape to distort and swelling to occur. Swelling and scarring destroy the clarity of the cornea, making it difficult for light to pass through. A distorted shape means that any light that does penetrate the cornea is not focused normally.
The disease known as keratoconus can cause a thinning cornea, which gradually protrudes forward forming a cone shape. Sometimes the cornea becomes swollen for weeks at a time and this leads to the development of scars. If the damage is severe, penetrating keratoplasty surgery may be carried out.
During penetrating keratoplasty surgery, the patient's whole cornea is removed using a circular cut before a circle of donated cornea is stitched into place. The operation takes about two hours and may not require an overnight stay in hospital. After a number of months the stitches are removed gradually, over the course of a year or more.
Endothelial keratoplasty surgery is usually performed when diseases such as Fuchs' endothelial dystrophy affect the cells which make up the inner lining, or endothelium, of the cornea. Fuchs' endothelial dystrophy causes the endothelial cells, which normally remove fluid from the cornea, to die off, and corneal swelling and cloudiness result. During the endothelial keratoplasty operation, a small cut is made in the eye through which the diseased endothelium is removed. Donated endothelial cells are then inserted in its place. If the surgery is successful, a great improvement in eye function may occur relatively quickly, in around six weeks.
Conductive keratoplasty surgery does not involve a cornea transplant. Instead, the shape of the cornea is changed to make it less flat, in order to improve its ability to focus light on the retina. The procedure uses energy from radio waves to shrink the outer circle of corneal tissue, causing the center to curve more steeply. Patients recover quickly and vision usually improves in about a week.