The window to our vision is the cornea. This clear, spherical structure covers the front of the eye, allowing light to pass through. The cornea’s curvature refracts (or bends), light as it travels to the retina, the back part of the eye where light is transformed to nerve signals that the brain then interprets as visual images.
But, like a glass window hit by a baseball, the cornea may be damaged and vision impaired. Sometimes, corneas can be repaired by laser eye surgery, which reshapes the cornea and restores proper function. But when the cornea is broken beyond repair, corneal transplants provide a new window on the world.
“Trauma, infection or certain genetic corneal diseases can lead to clouding, scarring, infection or swelling of the cornea, preventing light from entering the eye,” says Dr. Mujtaba Qazi, director of clinical studies at Pepose Vision Institute and a specialist in cornea and vision correction surgery. “In some cases, the health and clarity of the cornea, and therefore the vision, cannot be improved with medications, glasses or contact lenses. In these cases, a recommendation may be made to replace the cloudy cornea with clear transplant tissue.”
Patients who need new corneas receive the transplants from organ donors. The surgery may involve replacing the entire cornea or just one microscopically thin layer of tissue. “There are five layers to the cornea, and usually there are problems with either the middle layer (the stroma) or the back layer (the endothelium),” explains Dr. Steven Lee, an ophthalmologist with Ophthalmology Consultants. “The front part, the epithelium, is like your skin—it repairs itself and regenerates all the time. When you have an injury like a corneal abrasion, it is painful and takes time to heal, but it’s usually a quick process that works very well.” However, a damaged stroma or endothelium may scar and affect vision.
Unlike other types of organ transplants, corneal tissue is not typically rejected by the body, making these surgeries highly successful. Patients do not need to undergo tissue matching before receiving donated corneas. Yet the surgery is not simple, and there is a small risk of tissue rejection that must be monitored.
“Corneal transplantation is a major eye surgery with significantly greater associated short- and long-term risks,” Qazi says. “There are approximately 45,000 corneal transplants per-formed in the U.S. each year. It usually takes two to four times longer than cataract surgery, re-quires sutures, and either local or general anesthesia. Full visual rehabilitation can take three to 12 months, and patients will require long-term use of anti-rejection drops as there is a lifetime risk of rejection of the transplanted tissue.”
The surgery itself is intricate. Qazi describes the procedure involved in a partial-thickness corneal transplant: “Instead of making a full-thickness vertical incision, the posterior partial transplant tissue is folded like a cigar and injected into the eye. The donor tissue then unfolds and is pushed against the inner lining of the cornea with an air bubble. Over a few days, the air bubble becomes absorbed and disappears, but this gives the partial transplant tissue enough time to fuse with the patient’s cornea.”
Researchers continue to work toward ever-thinner transplant layers and the use of laser technology to improve the precision of the procedure. Synthetic corneas and tissue created from corneal stem cells also are being studied. Until these innovations are thoroughly tested and be-come part of standard practice, Lee and other experts continue to urge everyone to be organ donors. Your eyes could someday provide sight for another person.