When is corneal transplant surgery necessary?
The cornea is a clear dome of tissue that covers the front central portion of the eye. It functions primarily as the window to the eye. It allows light into the eye and bends (refracts) the light rays to help the lens focus them upon the retina. The normal cornea is completely transparent living tissue. To perform properly, the cornea must be crystal clear and be of a proper curvature.
Due to injury or disease, the cornea may become damaged and opaque or may develop uncorrectable changes in its curvature. If the cornea is not perfectly clear, light may no longer effectively pass through it, resulting in diminished vision. If the cornea is irregular or damaged, or irregularly curved, it will cause blurred vision. Replacing a cloudy, damaged, or cone-shaped corneal tissue with healthy donor tissue through a corneal transplant can make a dramatic improvement in vision.
There are many causes of clouding of the cornea. They include:
- Eye injuries that leave a dense white scar on the cornea. These injuries may include penetrating wounds from a sharp object, burns, or chemical contamination of the eye.
- A severe corneal infection that leads to corneal scarring. The infection may be bacterial, viral, or fungal in origin. Various herpes viruses are known to cause such scarring.
- Abnormal shapes of the cornea, such as occur with keratoconus, may scar the center of the cornea or distort vision so severely that glasses or contact lenses are of little help.
- Corneal dystrophies that may cause clouding
- Inherited diseases of the cornea
- Complicated cataract or eye surgery that can cause corneal decompensation, resultant swelling, and clouding. [UP]
How is corneal transplant surgery performed?
There are a variety of corneal transplant operations which may be performed under either a local or general anesthetic, depending upon what the doctor believes to be in the patient's best interests. Usually, the surgeon removes the center of the cloudy cornea and replaces it with a clear donor cornea. Sometimes if multiple layers of the cornea are involved in the patient’s disease process, the full thickness central cornea needs to be replaced, as in classic penetrating keratoplasty or PKP. Under other circumstances, only portions or layers of the cornea need to be replaced utilizing lamellar keratoplasty techniques such as the more recently developed DSEK (now the preferred procedure for most patients with a disease called Fuchs’ Corneal Dystrophy) and DALK procedures. [UP]
Risks
Just as is true with any operation, corneal transplant surgery entails some degree of risk. The success of the transplantation surgery is often related to the original cause of the underlying corneal disease process. Transplant procedures resulting from abnormally shaped corneas due to keratoconus or for corneal clouding following cataract surgery typically have very high success rates. Transplants due to scarring of the cornea from infections, such as herpes, may have a lower though still often very favorable success rate.
Perhaps the most common complication of corneal transplant surgery is corneal transplant rejection which can occur in about 1 in 10 patients but is usually reversible with anti-inflammatory drops. Corneal graft rejection most often occurs after 2 weeks and within 1 year post-operatively, but rarely may occur several years following corneal transplantation. Pain, light sensitivity, redness, and decreasing vision are warning signs of corneal transplant rejection and indicate the need for immediate medical attention. When started at the first signs of tissue rejection, steroids (drops, pills) are most often effective in halting the rejection process. Occasionally the rejection process does result in graft failure, resulting in blurry vision. Fortunately, only about 1 in 10 graft rejections episodes results in complete failure of the transplant and a repeat transplant is usually an option in this setting, often with a good visual result. [UP]
Convalescence
The eye is patched overnight and examined the next day. Usually, there is little or no discomfort after surgery.
In most cases, resumption of normal activities may occur soon after surgery with some reasonable limitations. For example, lifting heavy objects or strenuous exercise should be avoided until directed otherwise by the physician (usually 6 to 8 weeks). Until the eye has healed, glasses or an eye shield must be worn to protect the eye.
For several weeks following the transplant surgery, eye drops will be prescribed. The eye drops are to prevent infection and rejection of the donor corneal tissue.
Sutures when used to sew the donor cornea in place are barely visible and do not cause pain. It is normal for the eye to feel scratchy or irritated for the first few days following surgery. As the cornea heals, some of the stitches used to sew the donor tissue into place may need to be removed. This can be done quite easily and painlessly in the doctor's office.
During the first few weeks after surgery, vision may be quite blurry, as it takes time for the new cornea to completely heal and stabilize. Patients generally note steady improvement in vision over time however, and some of the newer lamellar transplant techniques (such as DSEK for Fuchs’ Dystrophy) are associated with substantially shorter recovery times. Once the cornea stabilizes, improved vision is usually achieved and glasses or contact lenses may be prescribed as necessary for best vision post-operatively. [UP]
