Introduction
One of the most exciting advances in corneal transplant surgery is the development of lamellar techniques for replacing damaged or dysfunctional corneal endothelium. To put these new techniques in perspective, one must recall that corneal transplant surgery had changed little over the previous 30 years, with the last major advances being the operating microscope, small diameter monofilament sutures, and the use of topical corticosteroids to prevent immunologic graft rejection.
Gerrit Melles, MD, developed and popularized the new technique of posterior lamellar keratoplasty (PLK)1-3 or, as it has been renamed in the United States, deep lamellar endothelial keratoplasy (DLEK). PLK is revolutionizing corneal transplantation for endothelial dysfunctions like Fuchs' endothelial dystrophy and pseudophakic bullous keratopathy.
PLK/DLEK offers many advantages over standard penetrating keratoplasty (PKP). First, a patient's dysfunctional endothelium is removed and replaced through a small incision that requires either no sutures or a few sutures that are removed in 2 months. Also, visual recovery is fast and spherical refractive surprises are virtually eliminated. Furthermore, ocular surface problems are minimal, which reduces the risk of early graft failure.
Most corneal surgeons have had a PKP patient who has fallen and reopened a PKP wound, sometimes many years after the PKP. This is especially tragic if the patient ends up losing the eye due to suprachoroidal hemorrhage. It is unfortunate that a PKP wound never heals to become as strong as virgin cornea. The PLK/DLEK technique now makes it possible to transplant corneal endothelium through a small beveled incision similar to that used in cataract surgery, which leaves the eye much stronger.
Just as it would now be unthinkable to perform an intracapsular cataract extraction instead of a small-incision phacoemulsification surgery, it soon may be unthinkable to perform a standard PKP for patients with Fuchs' dystrophy or pseudophakic bullous keratopathy except in unusual extenuating circumstances.
Original PLK/DLEK Technique
The PLK/DLEK surgical technique is rapidly evolving. Dr. Melles originally reported using a superior scleral approach with a 9-mm pocket incision. The trephine to be used to cut the donor tissue can also be used to lightly incise the epithelium of the recipient so that a reference mark is present to indicate where to excise the recipient tissue. A lamellar dissection of the recipient cornea is then performed by hand at 80% to 90% depth and extended out to the limbus (Slide 1, Slide 2, Slide 3). The cornea can be dissected with either a Matenez type corneal dissector or three dissecting blades of different lengths (DORC International, The Netherlands), two of which resemble curved and sharpened butter knives (Slide 1, Slide 2, Slide 3). The depth of the lamellar dissection can be estimated by filling the anterior chamber with air to create a light reflection between the air bubble and the tip of the dissecting blade (Slide 2).2
After completing the lamellar dissection, scissors of different shapes are used to excise a button of corneal tissue from the posterior corneal surface of the recipient (Slide 4). A similar lamellar dissection is then performed on the donor cornea. This can be done using a whole globe. However, because of time constraints to finish appropriate screen testing of donors, whole globes are seldom suitable for this in the United States, so the donor corneas are typically dissected on an artificial anterior chamber (Slide 5). Following dissection, the donor cornea is cut with a standard trephination system and the posterior portion can be laid on a spatula for insertion into the patient's eye. An air bubble injected into the anterior chamber presses the donor button up against the recipient bed until the natural pumping action of the endothelial cells creates suction between the donor and recipient tissue.
Advances in the PLK Technique
As an alternative to sliding the donor button into the eye on a spatula, Melles has pioneered folding the donor button into a taco shape using viscoelastic in the middle to protect the endothelium (Slide 6).3 This modification allows the donor button to be inserted through a smaller 4-mm to 6-mm incision (Slide 7). The wound can then be closed with two or three sutures to be removed at 1 month or, if a scleral tunnel incision is used, the surgery can be sutureless.
In a further modification of the technique, I have found a temporal clear corneal approach to be preferable to a superior scleral approach because it spares the limbus in case glaucoma surgery should ever be required. In addition, a temporal approach simplifies the surgical exposure and is potentially less likely to induce astigmatism - two reasons that a temporal approach is preferred for cataract surgery.
Simplified Procedure for Removing the Recipient Endothelium
The original PLK/DLEK technique involves three difficult steps:
- dissecting and removing the recipient corneal button
- dissecting the donor
- placing the donor into the recipient anterior chamber and maneuvering it into the correct position.
Of these, the process of dissecting and excising the button of tissue from the patient is the most challenging procedure.
Melles has recently introduced a simpler technique that involves scraping Descemet's membrane from the patient's eye instead of performing a lamellar dissection and excision. A Sinskey hook inserted through a paracentesis is used to cut through the recipient endothelium along the perimeter of the area to be transplanted (Slide 8). The recipient endothelium is then scraped off in one piece using a Melles scraper (DORC International) (Slide 9). Following removal from the eye, the recipient endothelium is laid on the surface of the eye to check that the size corresponds to the planned size of the donor button (Slide 10). As with the standard PLK procedure, the donor cornea is dissected, cut with a trephine, folded into a taco, inserted into the recipient anterior chamber (Slide 11 and Slide 12), unfolded, and pressed up against the recipient bed by an air bubble (Slide 13). The advantages of the new technique are that the most difficult step in the surgery is eliminated and, more importantly, the surface of the recipient bed is extremely smooth so that visual recovery should occur more rapidly and visual acuity potentially may be better.
Conclusion
PLK has similar advantages over standard PKP as phacoemulsification has over extracapsular surgery: the eye is left stronger and markedly more resistant to injury, and visual recovery is faster. For most patients, the overall quality of vision is also expected to be better after PLK compared to standard PKP. Some patients have excellent visual acuity after PKP, but some patients experience high or irregular astigmatism or lose an eye from wound rupture caused by minor trauma. PLK should mitigate the refractive problems of standard PKP and provide a much stronger eye that is resistant to trauma and rupture.4,5 The most recent modifications to the technique have greatly reduced the learning curve for this procedure and improved the quality of the donor/recipient interface, suggesting that PLK will soon become the technique of choice for treating endothelial disorders such as Fuchs' dystrophy or pseudophakic bullous keratopathy.
References
- Melles GR, Eggink FA, Lander F, et al. A surgical technique for posterior lamellar keratoplasty. Cornea. 1998;17 618-626.
- Melles GR, Rietveld F J, Beekhuis WH, et al. A technique to visualize corneal incision and lamellar dissection depth during surgery. Cornea. 1999;18:80-86.
- Melles GR, Lander F, Nieuwendaal C. Sutureless, posterior lamellar keratoplasty: a case report of a modified technique. Cornea. 2002;21:325-327.
- Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty in the first United States patients: Early clinical results. Cornea. 2001;20:239-243.
- Terry MA, Ousley PJ. In pursuit of emmetropia: Spherical equivalent refraction results with deep lamellar endothelial keratoplasty (DLEK). Cornea. 2003;22:619-626.
Posted April 2004