Endothelial Keratoplasty: Understanding DSEK and DSAEK
Endothelial keratoplasty (EK) is the selective replacement of diseased endothelium with healthy donor endothelium. First performed in humans in 1998 by Garret Melles, MD, from Netherlands, the procedure involved the removal of the endothelium and posterior stroma from a recipient cornea and replacement with a similarly sized donor stroma and endothelial tissue. Dr. Melles termed the procedure posterior lamellar keratoplasty (PLK).1 In March 2000, we modified the procedure, terming it deep lamellar endothelial keratoplasty (DLEK) and performed the first EK surgery in the United States.2 We have now performed various forms of EK in approximately 500 patients, as part of the largest and longest-running EK prospective study in the world.3
Three years ago, Dr. Melles proposed that stripping Descemet's membrane from the back of the recipient cornea would more easily remove the recipient endothelium (compared with cutting out the posterior stromal tissue) and would result in a smoother recipient interface surface. This modification has been popularized as Descemet's stripping endothelial keratoplasty (DSEK).4 When the donor tissue is prepared with a microkeratome instead of manually, the procedure has been termed Descemet's stripping automated endothelial keratoplasty (DSAEK), and this method is currently our preferred technique. The popularity of EK has grown with the evolution of DSEK/DSAEK because the procedure is now easier than it was with DLEK/PLK. Now, more surgeons feel comfortable performing EK surgery.5
At the Devers Eye Institute in Portland, Oregon, we perform >200 DSAEK transplants annually. We offer hands-on surgical training in EK each month here. Based upon the number of surgeons seeking EK training, I would estimate that about 40% of US surgeons now perform this procedure. By year-end, ≥70% of corneal transplant surgeons will be doing DSAEKs. The popularity of the procedure is also growing in Europe, where the trend is to stop performing penetrating keratoplasty (PK) in cases of endothelial dysfunction and start performing EK.
FASTER VISUAL REHAB
More surgeons are performing EK because it gives dramatically better results and faster visual rehabilitation compared with PK.1-5 Compared with full-thickness PK, prospective data showed that EK (ie, PLK/DLEK and DSEK/DSAEK) is far superior to PK in the endpoint measures of:
• Corneal astigmatism. With PK, the corneal astigmatism is highly unpredictable, regardless of the surgeon and the suturing technique. With EK, however, there is little or no change in astigmatism after EK.
• Spherical equivalent or refraction. After PK, it is unpredictable how steep or flat the cornea will be. Therefore we cannot predict the spherical equivalent/refraction. After EK, however, we can be very predictive of the spherical equivalent/refraction. Patients undergoing EK are more satisfied with their UCVA compared with those who undergo PK.
• Regularity of the surface. Irregular astigmatism occurs with almost every PK-corneal transplant. With EK, however, irregular astigmatism is very rare, resulting in a superior quality of vision with EK.
• Recovery time. After PK, the BCVA and stable visual acuity usually do not occur for at least 1 to 2 years. Sometimes, it is even longer. With EK, there is a faster recovery. Most patients have usable vision within 6 weeks after EK, and some patients have excellent vision at just 1 week.
• Incisions. A circular wound (7.5-mm to 8.5-mm diameter) cuts out the entire corneal thickness in PK. It is a vertical and unstable wound that never heals with any significant strength. Patients may have ruptured wounds and lose the eye from minor blunt trauma, even many years after the full-thickness surgery. During EK, a small 5-mm scleral incision is made, leaving the entire thickness of the recipient cornea untouched. This results in a comparatively normal tectonic strength of the eye with resistance to traumatic rupture for the rest of the patient's life.
PRESERVE THE ENDOTHELIUM
The highest priority of any EK surgery should be to preserve the donor endothelium. The surgeon must evaluate the effects that each surgical step will have on the donor endothelium. The surgeon must handle the donor tissue with care during its (1) mounting on the artificial chamber, (2) manual or automated technique cutting, (3) dismounting from the artificial chamber, (4) insertion into the recipient eye and (5) unfolding and positioning within the recipient anterior chamber. Each step is critical for preservation of the health and viability of the donor endothelial cells; the surgeon must always think about how he/she can better protect the donor endothelium during each stage of the procedure.
My personal DSAEK technique protects the donor endothelium by first coating it with sodium hyaluronate (Healon; Pfizer, New York, New York) and then mounting it on the artificial anterior chamber. I use Optisol (Chiron Ophthalmics, Irvine, California), the donor preservation media from the Eye Bank Association of America (Washington DC), to fill the entire system of the artificial chamber, avoiding saline or even balanced salt solution to come in contact with the donor endothelial surface. I use a three-way stopcock, attached to the syringe of the artificial anterior chamber system, to lock the proper pressure in place so there is little or no irrigation of the endothelium during the donor preparation process.
The following are a few more tips to conduct successful DSAEK: (1) Keep the tissue on the post of the artificial anterior chamber instead of removing it attached to the cap or helmet of the artificial anterior chamber device. This will avoid anterior chamber collapse and prevent donor endothelial cell damage during dismounting of the tissue from the artificial anterior chamber. (2) Insert and unfold the tissue without an infusion line into the recipient anterior chamber and without touching the endothelium. (3) Do not fold the tissue more than what we advocate (ie, a 60/40% fold). A single fold damages the endothelial cells, but a triple fold will cause two or three times more damage to the endothelium.
During the upcoming American Academy of Ophthalmology meeting in November, we will present our DSAEK techniques and videos that demonstrate how to prevent dislocation and corneal graft failure. In our initial 100 cases of DSEK/DSAEK,6 our dislocation rate was 4%, and our primary graft failure rate was 1%. This is the lowest published rate in the world. In our current series, the rate is even lower.
MODIFIYING THE TECHNIQUE
Some surgeons are experimenting with (1) a 3-mm DSEK/DSAEK incision and (2) moving the incision from the sclera to the clear cornea. Surgeons are trying new techniques to make the surgery easier and faster. While we favor cataract surgery through smaller incisions, we must keep in mind that corneal transplantation surgery is not cataract surgery. In EK surgery, squeezing living tissue that is ≥8 mm through a 3-mm incision increases the likelihood — in my opinion — of damage to that tissue. The surgeon must assess: Is tissue damage for the patient worth the advantage for the surgeon? A smaller incision may save 5 minutes during the procedure, but it holds no advantage for the patient. No data support reducing the scleral access incision size from 5 mm to 3 mm and squeezing the tissue through this smaller incision. There is no advantage for the patient regarding astigmatism and visual quality. In fact, significant disadvantages of using a 3-mm incision may include higher endothelial cell loss, a higher primary graft failure rate and late endothelial failure.
My recommendation is that any change to the surgical technique of EK must be weighed against the patient disadvantages and backed up with data. There are many modifications that are being done with this surgery, and it is exciting to see surgeons trying to improve the procedure. But, I caution against changing the procedure to make it easier for the surgeon without knowing whether it might not be worse for the patient.
I believe that EK is the future of corneal transplantation surgery. If surgeons use a technique that is easy and safe for their patients, EK surgery will eventually fully replace PK for our patients suffering from endothelial disease.
Mark A. Terry, MD, is director of corneal services at Devers Eye Institute, in Portland, Oregon. Dr. Terry states that he has a royalty financial interest with Bausch & Lomb Surgical (Rochester, New York) in the specialized instruments he designed for EK surgery. He may be reached at MTerry@DeversEye.org or +1 503-413-6223.
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