Penetrating keratoplasty, often called a full-thickness corneal transplant, is a surgical procedure that replaces a damaged or diseased central cornea with healthy tissue from a deceased human donor. The cornea, the clear outer layer at the front of the eye, acts like a window, bending light rays as they enter the eye to create clear vision. When this transparent tissue becomes clouded, misshapen, or scarred, light cannot pass through properly, leading to impaired vision. In such cases, replacing the entire thickness of the cornea becomes a necessary intervention to restore visual clarity.
Conditions Requiring a Full-Thickness Transplant
A full-thickness corneal transplant becomes necessary when damage extends through all layers of the cornea, making other treatments ineffective. One common reason is advanced keratoconus, a condition where the cornea progressively thins and bulges outward into a cone shape, significantly distorting vision. When the irregular curvature becomes too severe for correction with glasses or contact lenses, a full-thickness replacement can restore a proper optical surface.
Significant corneal scarring, often resulting from severe infections like herpes keratitis or traumatic injuries, also frequently necessitates a penetrating keratoplasty. Such scars can block light from entering the eye, leading to substantial vision loss. Similarly, bullous keratopathy, characterized by corneal swelling and clouding due to fluid buildup, can severely impair vision and cause discomfort, making a full-thickness graft a suitable option.
Certain inherited corneal dystrophies, such as Fuchs’ dystrophy, may also progress to a point where they affect both the front and back layers of the cornea, causing widespread clouding and swelling. Previous corneal grafts that have failed due to various complications, including rejection or age-related changes, also represent a common indication for a repeat penetrating keratoplasty to restore functional vision.
The Surgical Procedure
The penetrating keratoplasty procedure begins with the administration of anesthesia, which can be local with sedation or general, depending on the patient’s condition and surgeon’s preference. Once the eye is prepared, a circular surgical instrument called a trephine is used to precisely remove the diseased central portion of the patient’s cornea, creating a circular opening. This step requires careful measurement to ensure the correct size for the donor tissue.
Following the removal of the damaged tissue, a healthy donor cornea, prepared to match the recipient’s eye, is positioned. The donor tissue is then carefully sutured into place. Very fine stitches are used to secure the new cornea, ensuring proper alignment and tension to minimize astigmatism.
The entire operation is performed under an operating microscope, allowing the surgeon to work with precision. The surgery lasts one to two hours and is often performed on an outpatient basis, with patients usually going home the same day.
The Recovery and Healing Process
Immediately following penetrating keratoplasty, a protective eye shield is placed over the operated eye, and patients may experience mild discomfort. A follow-up appointment is scheduled for the next day, where the shield is removed, and the surgeon assesses the initial healing. Patients are instructed to wear the eye shield at night for a period to protect the new cornea from accidental injury during sleep.
Medicated eye drops, including steroid and antibiotic formulations, are important in the recovery process. Antibiotic drops are prescribed to prevent infection, while steroid drops are used for an extended period to reduce inflammation and suppress the immune system’s response to the donor tissue, thereby preventing rejection. Consistent and accurate application of these drops is important for successful healing.
Activity restrictions are in place to protect the healing eye. Patients are advised to avoid bending over, heavy lifting, and strenuous activities for several weeks. Contact sports are prohibited for an extended period due to the risk of a severe blow separating the graft. While reading and watching television are permitted, activities that could introduce dust or dirt into the eye should be avoided.
Vision improvement following a penetrating keratoplasty is gradual and can take a considerable amount of time for full stabilization. It is common for vision to be blurry initially as the eye adjusts to the new cornea. Most patients will require glasses or contact lenses after surgery to correct astigmatism, which is a common outcome due to the curvature induced by the sutures.
The fine sutures holding the donor cornea in place remain for an extended period. These sutures may be removed gradually in the surgeon’s office once the eye has healed sufficiently and vision has stabilized. Suture removal can sometimes help reduce astigmatism and further refine vision.
Understanding Graft Rejection
Graft rejection is a long-term risk following penetrating keratoplasty, occurring when the recipient’s immune system identifies the donor corneal tissue as foreign and attacks it. This immune response can happen at any time after surgery, though most rejections occur within the first year. While the cornea is considered an “immune privileged” site, rejection is still possible.
Recognizing the warning signs of rejection early is important for prompt treatment. Patients are advised to watch for symptoms that can be remembered by the acronym RSVP: Redness in the eye, Sensitivity to light (photophobia), Vision decrease or blurriness, and Pain. If any of these symptoms appear, contacting the surgeon immediately is important.
When caught early, graft rejection can be reversed with prompt medical treatment. This involves intensive use of steroid eye drops to suppress the immune response. In more severe cases, oral steroids or other immunosuppressive medications may be prescribed. A rejection episode does not automatically mean the graft will fail; many can be successfully managed, preserving the transplanted cornea.