Penetration Keratoplasty (PKP)
Penetrating keratoplasty (“full-thickness” corneal transplant) is the traditional form of corneal transplants and involves surgical removal of the central part of the damaged cornea. The full thickness of the cornea in this region is removed and replaced with clear, healthy donor tissue held in place by sutures. Full visual recovery usually takes approximately one year, and patients may require glasses or contact lenses to refine their vision, as the corneal surface is frequently irregular after PKP. Some of the risks associated with PKP include infection, bleeding, poor surface healing, wound leak, rejection, graft failure, retinal detachment/swelling, astigmatism, glaucoma, and inflammation.
Deep Anterior Lamellar Keratoplasty (DALK)
The outer layers or front portion of the cornea can be replaced selectively when it is scarred or distorted. This procedure is known as DALK. It involves separating the cornea of the patient into front and back portions. The front, scarred portion is removed and the healthy back portion remains. A matching piece of healthy donor tissue is then used to replace the front portion removed during surgery. This procedure is less invasive (“partial-thickness” corneal transplant) than a PKP, and the recovery time is quicker. Furthermore, the risk of graft rejection is lower. Only select patients can undergo this procedure. Some of the risks associated with DALK include perforating the back portion of the cornea during surgery, infection, poor surface healing, rejection, graft failure, astigmatism, glaucoma, and inflammation.
Endothelial Keratoplasty (EK)
Endothelial keratoplasty is another form of “partial-thickness” corneal transplants, but treats diseases that affect the back layer (endothelium) of the cornea and cause swelling. During the procedure, the diseased back layer is removed and replaced with donor tissue. The two main types of endothelial keratoplasty are DSAEK (Descemet’s Stripping Automated Endothelial Keratoplasty) and DMEK (Descemet’s Membrane Endothelial Keratoplasty). For both DSAEK and DMEK the donor tissue is held in place by an air bubble postoperatively. Patients must lie on their back for 1-3 days after surgery to allow the bubble to float up and make the donor tissue stick. The body gradually absorbs the bubble within a week. Occasionally, the eye may need some more air to keep the donor graft in place after surgery. Overall healing takes about 4-6 months. Some of the risks associated with EK include infection, graft detachment, bleeding, poor surface healing, wound leak, rejection, graft failure, retinal detachment/swelling, glaucoma, and inflammation.
Here is a video showing DMEK surgery in which the corneal transplant tissue is much thinner, healing time is faster, and vision may be better.
A keratoprosthesis is an artificial cornea. Artificial corneas have become more reliably successful over the last few years. For most patients, human donor tissue still provides the best results; however, some conditions predispose patients to a high risk for failure. For example, those with multiple previous graft failures and/or severe ocular surface diseases have a much better prognosis with a keratoprosthesis, achieving potentially excellent visual outcomes. For disease affecting the full-thickness of the cornea, we use a full-thinkness KPro called the Boston KPro. With this surgery, the prosthesis is secured to donor corneal tissue which is then sutured to the eye. After surgery, patients are required to wear a contact lens as well as use antibiotic and steroid eye drops indefinitely. Close follow-up with an ophthalmologist is essential to monitor for complications associated with the device. Some of the risks associated with the Boston KPro include development of a membrane behind the KPro, glaucoma, inflammation, infection, bleeding, poor surface healing, corneal thinning, wound leak, extrusion, and retinal detachment/swelling. For disease that affects the front part of the cornea, we use a partial-thickness KPro called the KeraKlear KPro. In this surgery, a femtosecond laser is used to make a pocket in the front part of the cornea and the KPro is inserted into the pocket. Contact lens wear is usually needed after surgery. The KeraKlear KPro is less invasive than the Boston KPro. Some of the risks associated with the KeraKlear KPro include infection, corneal thinning, and device extrusion.
ICRS are clear, thin, semi-circular corneal implants which are placed within the cornea. They are used in the treatment of keratoconus to help to reinforce the structural integrity of the cornea and gently reshape the curvature of the cornea. This can be done to increase contact lens tolerance. These implants are no more visible than a contact lens and cannot be felt after insertion. Intacs require no maintenance and they can be removed or replaced if necessary.
Corneal collagen cross-linking is a procedure done to stiffen and stabilize a cornea that is undergoing an uncontrolled change in shape (for example in keratoconus or ectasia after LASIK). Riboflavin (vitamin B2) drops are instilled into the eye over a period of 30-60 minutes and then the cornea is exposed to UV light for 5-30 minutes. The combination of the riboflavin drops and the UV light will strengthen the bonds within the cornea to stiffen it. This procedure is sometimes performed in conjuction with other procedures such as topography-guided PRK, PTK and/or Intacs.