WHAT IS THE CORNEA?
The cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. It is the most powerful tissue in the eye to help us focus and see. If the cornea is not clear it can be replaced with a cornea transplant.
Structure of the Cornea
Although the cornea is clear and seems to lack substance, it is actually a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. The cornea must remain transparent to refract light properly, and the presence of even the tiniest blood vessels can interfere with this process. To see well, all layers of the cornea must be free of any cloudy or opaque areas.
The corneal tissue is arranged in five basic layers, each having an important function. These five layers are:
The epithelium is the cornea’s outermost region, comprising about 10 percent of the tissue’s thickness. In advanced corneal disease blisters may form on the corneal endothelium. They are an indication of corneal failure and can initially be treated. Rupture of the blisters is painful.
Lying directly below the basement membrane of the epithelium is a transparent sheet of tissue known as Bowman’s layer. It is composed of strong layered protein fibers called collagen.
Beneath Bowman’s layer is the stroma, which comprises about 90 percent of the cornea’s thickness. It consists primarily of water (78 percent) and collagen (16 percent), and does not contain any blood vessels. Collagen gives the cornea its strength, elasticity, and form. The collagen’s unique shape, arrangement, and spacing are essential in producing the cornea’s light-conducting transparency.
Under the stroma is Descemet’s membrane, a thin but strong sheet of tissue that serves as a protective barrier against infection and injuries.
The endothelium is the extremely thin, innermost layer of the cornea. Endothelial cells are essential in keeping the cornea clear. Normally, fluid leaks slowly from inside the eye into the middle corneal layer (stroma). The endothelium’s primary task is to pump this excess fluid out of the stroma. Without this pumping action, the stroma would swell with water, become hazy, and ultimately opaque. In a healthy eye, a perfect balance is maintained between the fluid moving into the cornea and fluid being pumped out.
Normal Corneal Endothelium:
Abnormal Corneal Endothelium
Once endothelium cells are destroyed by disease or trauma, they are lost forever. If too many endothelial cells are destroyed, corneal edema and blindness ensue, with corneal transplantation the only available therapy. Fuch’s corneal disease is a disease of the endothelium [black cells damaged].
How common are cornea transplants ?
Cornea transplants are a very routine procedure. Dr. Duplessie has performed hundreds of corneal transplants. Dr. Duplessie performed one of the first sutureless corneal transplants in the United States and was selected to write one of the first textbook chapters on Lamellar Surgery.
He is an expert in the advanced corneal transplant techniques such as PKP, ALK, ALTK, DLEK, DSAEK, Deep Anterior Lamellar Keratoplasty (DALK).
Corneal transplants are used when the cornea is severely damaged. Injury to the cornea can occur because of congential corneal diseases, burns from chemicals, mechanical trauma, or infection by viruses, bacteria, fungi, or protozoa. Herpes virus is one of the more common infections leading to corneal transplant.
Surgery would only be used when damage to the cornea is too severe to be treated with corrective lenses. Occasionally, corneal transplant is combined with other types of eye surgery and is used frequently with cataract surgery solve multiple eye problems in one procedure.
What is involved in performing corneal transplant surgery?
Eye drops will be put in the eyes. A sedative will be given . The patient will be taken to the operating room and given a local anesthesia and iv sedation. Corneal transplants are painless procedures and typically take an hour.
Once the corneal transplant is completed, a patch and protective metal shield will be placed over the operated eye. Patients are sent to the recovery room where they will be observed before being discharged home with family and friends.
What are the risks involved with cornea transplant surgery?
As with most surgeries, there are always risks involved with any surgical procedure. These problems can usually be divided into two categories. These are those that occur at the time of the surgery itself and those that take place after this surgery.
These risks are similar to those associated with other types of ocular surgery such as glaucoma and cataract surgery. Problems which can occur afterward include glaucoma, infection, retinal swelling or detachment,and cataracts. Rarely, there can be loss of all sight.