The Cornea and Corneal Transplants
EYE CARE
Florida Eye Associates' Dr. Payman Haft completed his cornea fellowship and residency at the prestigious Bascom Palmer Eye Institute at the University of Miami.
BREVARD COUNTY, FLORIDA – The cornea is the eye's outermost layer. It is the clear, dome-shaped surface that covers the front of the eye that helps protect the rest of the eye from germs, dust, and other harmful matter.
The cornea serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and the retina would be highly susceptible to injury from UV radiation. It also acts as the eye's outermost lens.
Light passes through this transparent surface 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 areas.
The cornea copes very well with minor injuries or abrasions – of it is scratched, healthy cells slide over quickly and patch the injury before infection occurs and vision is affected.
The cornea serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight.
If the scratch penetrates the cornea more deeply, however, the healing process will take longer, at times resulting in greater pain, blurred vision, tearing, redness, and extreme sensitivity to light.
These symptoms require professional treatment. Deeper scratches can also cause corneal scarring, resulting in a haze on the cornea that can greatly impair vision. In this case, a corneal transplant may be needed.
Some diseases and disorders of the cornea that can result in transplant are:
• Corneal Infections. Sometimes the cornea is damaged after a foreign object has penetrated the tissue, such as from a poke in the eye. At other times, bacteria or fungi from a contaminated contact lens can pass into the cornea. Situations like these can cause painful inflammation and corneal infections called keratitis.
These infections can reduce visual clarity, produce corneal discharges, and perhaps erode the cornea. Corneal infections can also lead to corneal scarring, which can impair vision and may require a corneal transplant.
As a general rule, the deeper the corneal infection, the more severe the symptoms and complications. Corneal infections, although relatively infrequent, are the most serious complication of contact lens wear.
• Fuchs' Dystrophy. Fuchs' dystrophy is a slowly progressing disease that usually affects both eyes and is slightly more common in women than in men. Although doctors can often see early signs of Fuchs' dystrophy in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s.
Fuchs' dystrophy occurs when corneal endothelial cells gradually deteriorate without any apparent reason. As more endothelial cells are lost over the years, the endothelium becomes less efficient at pumping water out of the stroma. This causes the cornea to swell and distort vision. Eventually, the epithelium also takes on water, resulting in pain and severe visual impairment.
Sometimes the cornea is damaged after a foreign object has penetrated the tissue, such as from a poke in the eye.
Epithelial swelling damages vision by changing the cornea's normal curvature, and causing a sight-impairing haze to appear in the tissue. Epithelial swelling will also produce tiny blisters on the corneal surface. When these blisters burst, they are extremely painful.
At first, a person with Fuchs' dystrophy will awaken with blurred vision that will gradually clear during the day. This occurs because the cornea is normally thicker in the morning; it retains fluids during sleep that evaporate in the tear film while we are awake. As the disease worsens, this swelling will remain constant and reduce vision throughout the day.
When treating the disease, doctors will try first to reduce the swelling with drops, ointments, or soft contact lenses. They also may instruct a person to use a hair dryer, held at arm's length or directed across the face, to dry out the epithelial blisters. This can be done two or three times a day.
When the disease interferes with daily activities, a person may need to consider having a corneal transplant to restore sight. The short-term success rate of corneal transplantation is quite good for people with Fuchs' dystrophy. However, some studies suggest that the long-term survival of the new cornea can be a problem.
Other Corneal Dystrophies
A corneal dystrophy is a condition in which one or more parts of the cornea lose their normal clarity due to a buildup of cloudy material. There are over 20 corneal dystrophies that affect all parts of the cornea.
These diseases share many traits:
- They are usually inherited.
- They affect the right and left eyes equally.
- They are not caused by outside factors, such as injury or diet.
- Most progress gradually.
- Most usually begin in one of the five corneal layers and may later spread to nearby layers.
- Most do not affect other parts of the body, nor are they related to diseases affecting other parts of the eye or body.
- Most can occur in otherwise totally healthy people, male or female.
Corneal dystrophies affect vision in widely differing ways. Some cause severe visual impairment, while a few cause no vision problems and are discovered during a routine eye examination. Other dystrophies may cause repeated episodes of pain without leading to permanent loss of vision.
Corneal Transplant
Corneal transplant involves replacing a diseased or scarred cornea with a new one. When the cornea becomes cloudy, light cannot penetrate the eye to reach the light-sensitive retina. Poor vision or blindness may result.
In corneal transplant surgery, the surgeon removes the central portion of the cloudy cornea and replaces it with a clear cornea, usually donated through an eye bank.
The cloudy cornea is removed and the surgeon places a new cornea in the opening and sews it with a very fine thread. The thread stays in for months or even years until the eye heals properly (removing the thread is quite simple and can easily be done in an ophthalmologist's office). Following surgery, eye drops to help promote healing will be needed for several months.
Even with a fairly high success rate, some problems can develop, such as rejection of the new cornea. Warning signs for rejection are decreased vision, increased redness of the eye, increased pain, and increased sensitivity to light.
If any of these last for more than six hours, you should immediately call your ophthalmologist. Rejection can be successfully treated if medication is administered at the first sign of symptoms.
Are there alternatives to a corneal transplant?
Descemet's stripping endothelial keratoplasty (DSEK) replaces only the endothelium (innermost layer of the cornea), rather than the entire thickness of the cornea. DSEK involves peeling only the diseased endothelial layer from the back of the patient's cornea, leaving the remaining 95 percent of the cornea, which is healthy, untouched.
The back layer of a healthy donor cornea is then placed inside the eye through a small incision and positioned with an air bubble to replace the diseased layer that was removed.
After the surgery a patch will be place on the eye and the patients should try to lie down on the back, facing the ceiling as much as possible for the first 24 hours, until seen back the next day.
Advantages of DSEK as compared to standard corneal transplantation are:
- The eye is left much stronger and more resistant to injury
- There is minimal change in refractive error because the patient's cornea is essentially intact
- Suture-related problems can be eliminated
- Visual recovery is significantly faster and better
- DSEK offers patients better visual recovery and a less protracted clinical course than standard corneal transplantation.
Phototherapeutic keratectomy (PTK) is another of the latest advances in eye care for the treatment of corneal dystrophies, corneal scars, and certain corneal infections.
Phototherapeutic keratectomy (PTK) is another of the latest advances in eye care for the treatment of corneal dystrophies, corneal scars, and certain corneal infections. Only a short time ago, people with these disorders would most likely have needed a corneal transplant.
By combining the precision of the excimer laser with the control of a computer, doctors can vaporize microscopically thin layers of diseased corneal tissue and etch away the surface irregularities associated with many corneal dystrophies and scars.
Surrounding areas suffer relatively little trauma. New tissue can then grow over the now-smooth surface. Recovery from the procedure takes a matter of days, rather than months as with a transplant. The return of vision can occur rapidly, especially if the cause of the problem is confined to the top layer of the cornea.
Corneal surgery has improved dramatically because of technological improvements, such as better supplies, the advent of laser technology and other advances in medicine. Sight can be restored to many, who a generation ago would have been blinded permanently by corneal injury, infection, or inherited corneal disease or degeneration.
Payman Haft, MD is a fellowship trained cornea specialist with Florida Eye Associates in Melbourne, Florida. He completed his cornea fellowship and residency at the prestigious Bascom Palmer Eye Institute at the University of Miami. He is accepting new patients starting September 14, 2009. For more information or to schedule an appointment, please call 321-727-2020 or CLICK HERE for more information.
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Florida Eye Associates founder, Dr. William Broussard, and his wife, Margaret, founded the Allen Broussard conservancy, a not-for-profit scientific corporation dedicated to the memory of their son Allen and created for the purpose of purchasing the land and keeping it as a wildlife preserve.
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