Penetrating keratoplasty (PKP), often called a full corneal transplant, is a surgical procedure that replaces the entire thickness of the damaged or diseased cornea. The cornea is the clear, dome-shaped outer layer at the front of the eye, which focuses light onto the retina. When this layer becomes clouded or misshapen, vision can be severely compromised, and PKP may be necessary to restore clarity. This surgery replaces the patient’s compromised corneal tissue with healthy, clear tissue from a human donor. This complete replacement is chosen when the damage extends through all corneal layers, making partial-thickness transplants insufficient.
Conditions Requiring a Full Corneal Transplant
PKP is necessary when corneal damage is extensive and irreparable across all layers, such as when the cornea is severely scarred, swollen, or misshapen. This full-thickness replacement is required because less invasive procedures, which replace only specific layers, are not an option in these advanced cases.
One common condition requiring a full transplant is advanced keratoconus, a disorder where the cornea thins and bulges into a cone shape, leading to severe visual distortion. While early-stage keratoconus can often be managed with specialized contact lenses, a transplant becomes necessary when the cornea is too compromised or scarred. Severe corneal scarring from prior infections, such as microbial keratitis, or from physical trauma and chemical injuries also necessitates a PKP.
Conditions affecting the innermost layer, the endothelium, such as Fuchs’ endothelial dystrophy or bullous keratopathy, also frequently require a full transplant. These disorders cause swelling and clouding because the endothelial cells fail to pump fluid out properly. PKP is also used when a previous corneal transplant has failed and the entire graft needs replacement.
The Penetrating Keratoplasty Procedure
Before surgery, the donor corneal tissue is prepared, having been procured from an eye bank and screened for diseases. The procedure is typically performed on an outpatient basis using either local or general anesthesia. The patient’s eyelids are held open with a specialized instrument while the eye’s surface is prepared.
The surgeon uses a circular cutting instrument, called a trephine, to precisely remove a central, full-thickness disc of the patient’s diseased cornea. A matching trephine cuts the donor cornea to a slightly larger diameter, often by about 0.25 to 0.5 millimeters, which ensures a tight fit. The host’s diseased corneal tissue is carefully resected using a blade and curved corneal scissors to create the opening.
The new donor corneal tissue is placed into the opening and secured with extremely fine nylon sutures. The surgeon uses either a running suture, interrupted sutures, or a combination of both, placing them with equal tension to minimize post-operative astigmatism. The knots are often rotated into the corneal tissue to prevent irritation.
Post-Surgical Recovery and Monitoring
Recovery after a PKP requires strict adherence to post-operative instructions. Immediately following surgery, patients are given medicated eye drops, including potent topical steroids and antibiotics, to prevent infection and manage inflammation. Steroid drops suppress the body’s immune response and significantly reduce the risk of graft rejection, often continuing long-term.
Patients must follow several restrictions in the immediate post-operative period, such as avoiding strenuous activity, heavy lifting, and anything that could cause direct injury or pressure to the eye. Follow-up appointments are frequent, beginning the day after surgery, to monitor the graft’s health, check eye pressure, and assess healing. The fine sutures holding the graft in place are a major factor in the long-term visual outcome.
Suture removal is a gradual process that can take many months to over a year, with timing dependent on the graft’s healing and the presence of astigmatism. The body’s immune system can still identify the donor tissue as foreign, leading to graft rejection, which can occur at any time, even years after the procedure. Symptoms of rejection include redness, increased light sensitivity, pain, and decreased vision, requiring immediate and aggressive treatment with steroids to save the graft.