Penetrating keratoplasty (PKP) is a surgical procedure to remove a diseased or damaged part of the cornea followed by implantation of healthy tissue from a human donor. It is often used to treat keratoconus, a condition marked by the progressive thinning and steepening of the cornea leading to myopia and irregular astigmatism.
Various options to attain visual acuity include spectacles, contact lenses, keratoplasty, and intracorneal rings. PKP is performed when the patient reaches the loss of the best spectacle-corrected visual acuity (BSCVA) stage. The cornea may be too steep or too flat to be treated by other methods. Patients with apical scarring or contact lens failure are also likely PKP candidates. It can also be used when the cornea is affected by injury, infection, previous surgery, or diseases such as keratitis, Fuch's dystrophy, and corneal ulceration. It is known as full-thickness because the transplantation replaces all five layers of the cornea.
Partial-thickness techniques have supplanted PKP due to less stromal scarring. However, PKP is still used in conditions with significant stromal scarring, corneal ectasia (bilateral thinning of the peripheral cornea), opacities, and significant posterior corneal involvement such as keratoconus and Peter’s anomaly. PKP takes care of diseases involving the epithelial, stromal, and endothelial layers.
Also Known As
- Corneal Graft
- Corneal Transplant
- Corneal Transplantation
Preparation & Expectation Before Surgery
The doctor will take a patient's ocular history and visual acuity. A detailed examination will be done, including taking intraocular pressure, finding out if there are any underlying causes, and checking for the presence of a cataract. The doctor also checks for the tear film status and signs of abnormal blood vessel formation.
Types, Purpose & Procedure
The patient is put through local or general anesthesia. It's essential to involve the patient in selecting which anesthesia to use because some patients may suffer from anxiety if they are conscious. The procedure is performed in the outpatient setting and will last one to two hours. The surgeon:
- Uses a speculum to keep the eyelids open
- Uses a Sinskey hook to mark the host cornea's center. S/he measures the corneal diameter using calipers to determine how much donor tissue to use
- Removes a circle of tissue from the donor tissue using a trephine
- Removes a circle of tissue from the host cornea
- Injects Healon into the anterior chamber for depth and stability
- Uses curved corneal scissors to resect the host corneal tissue
- Replaces the damaged tissue with matching donor tissue using stitches
- Places sutures and assesses astigmatism using a keratometer
Sometimes PKP may be done in combination with other procedures such as secondary intraocular lens implantation, glaucoma surgery, cataract surgery, and retinal surgery. In the case of retinal surgery, the surgeon sutures a temporary keratoprosthesis to enable visualization of the posterior segment. Once retinal surgery is complete, the surgeon replaces the temporary keratoprosthesis with permanent corneal graft.
Risks, Side Effects & Complications
Though rare, excessive bleeding can result from PKP. There is also a higher lifetime risk of wound dehiscence because the tectonic strength from a full-thickness wound is compromised.
Risks associated with PKP postoperatively include scarring, postsurgical infection, wound leakage from the incision site, inflammation of the eye’s interior, persistent epithelial defect, and cataract formation. Others include primary endothelial failure, a bacterial infection of the cornea, glaucoma, and recurrence. There is also a substantial postoperative refractive error caused by high or irregular astigmatism of the graft. Refractive errors include astigmatism, hyperopia, and myopia. Corrective eyeglasses or contact lenses (rigid gas permeable) can address vision problems caused by a refractive error that occurs following PKP.
There is a higher risk of graft rejection in PKP than in the other keratoplasty types of transplantations. If a patient experiences eye irritation and decreased vision, the patient should immediately visit the ophthalmologist because those are signs that the body is rejecting the donated tissue. Other indications that the donor cornea is undergoing rejection include pain, photophobia, redness, and a white line on the corneal endothelium. Stromal edema (excess fluid in the stroma), subepithelial or epithelial edema, conjunctival injection, and formation of new blood cells are also signs that the new cornea is being rejected.
Patients should note that rejection can happen even years after transplantation, hence the need for vigilance. However, medications can be used to prevent or treat rejection of the new corneal tissue. The doctor will first prescribe topical steroids such as prednisolone 1% to be taken immediately, in the first hour of rejection. S/he may consider systemic steroids (prednisone 40-80 mg daily) if a patient does not respond to topical steroids and cases where recurrent rejection occurs.
Complications can occur intraoperatively. They may include:
- Lens damage
- Poor graft centration
- Damage to donor tissue
- Irregular trephination (making a hole)
- Incarceration of iris tissue in the wound
- Choroidal hemorrhage and effusion (accumulation of fluid)
- Vitreous (a gel-like substance) in the anterior chamber
After Care, Recovery, & Results
The patient will be prescribed eye drops for self-administration. S/he must also avoid high-risk activities that may injure the eye such as sports.
PKP often results in a slow improvement in vision unless the graft has been rejected. It may take up to one year or years for a patient to have vision restored to a satisfactory level or achieve best-corrected visual acuity. During this period of recovery, patients wear contact lenses or corrective glasses. Sutures are often removed after one year unless complications like vascularization, loosening, and cheese-wiring occur.
For patients with keratoconus, PKP produces good visual outcomes with a high chance of graft survival and a low complication rate.