Eyeworld

EW FEATURE 39 bothersome is that the cell loss con- tinues thereafter at an accelerated pace compared to what normal non- operated cornea cell loss would be," Dr. Verdier said. "We are quite fear- ful that many of our younger pa- tients are going to run out of cells before the end of their life and will not have a transplant that lasts a lifetime." This is particularly important because many corneal procedures are done in younger adults. "Many anterior lamellar keratoplasty for keratoconus and corneal stromal dy- strophies are performed quite often in people under age 40," Dr. Verdier said. There's no question that the endothelial cell loss with DALK is much less. "We know that the cell loss is somewhere between 10-15% after 2 years, but then it seems to settle down to what the normal cell loss or near what the normal cell loss is in an un-operated cornea," Dr. Verdier said. "Preliminary data is very positive suggesting that the en- dothelial cell loss will be dramati- cally less in DALK." Also, with DALK, concerns about graft rejection are vastly re- duced. "The rejection of the great majority of corneal grafts are en- dothelial and we take that totally out of the picture by retaining the patient's own endothelium," Dr. Verdier said. "So the biggest problem with corneal transplant failure his- torically in PK is rejection and even without rejection, late endothelial failure, which is also a significant issue." The third issue plaguing PK is surface disease. While DALK does nothing to alleviate this, Dr. Verdier still sees it as an improved proce- dure, which has eliminated two of the three big problems associated with PK. While there is no long-term data on this yet, the evidence sug- gests DALK will only need to be done once. "I think that almost all of us feel that if you can pull it off and complete the procedure well, the transplant is very likely to last the patient's lifetime," Dr. Verdier said. He sees this as important for several reasons. "You increase your chance of rejection when you go back for a second or a third proce- dure," he said. In addition, rehabili- tation after corneal transplantation can be much more taxing than other commonly performed visual proce- dures. "Cataract patients see better within weeks, and PK patients see better within a year or two. It's a long period of not seeing very well." Additionally, in about 1% of cases, PK patients run the risk of having an expulsive hemorrhage. "That's a devastating event," Dr. Verdier said. "People lose their vi- sion permanently from one of those. The risk of this is pretty much elimi- nated when Descemet's membrane is preserved." "The other problem with PK is that at some point in their life, about 5% of our PK patients end up with a ruptured globe through trauma," Dr. Verdier said. "This is usually inadvertent." Unfortunately, he finds that at least half of those people never see well afterward. On the other hand, with DALK he feels that there is less chance of this oc- curring. "It looks like even though the only thing that we're preserving in DALK is the endothelium and Dedcemet's, which is about 1% of the cornea, that membrane is tough enough to be a barrier to trauma," he said. All of this considered, Dr. Verdier pointed out that there is much to gain and little to lose by at- tempting a DALK procedure. "I know that if it was my own family member or me, I would rather have the DALK done," he said. If you fail with the DALK you can always con- vert to a PK right there on the table. "There's no extra morbidity or loss of outcome for the patient. It's as if you did the PK in the first place," Dr. Verdier said. Performing DALK Dr. Holland has already made the switch to DALK. For the procedure, he likes the big bubble technique. "In my hands it has worked the best," he said. While there are different ways to do this, he has a couple of tricks that he finds helpful. "I trephine down to about 90%," Dr. Holland said. "Then what I think is really im- portant is to get a deep dissection to pre-Descemet's." He starts out with a super sharp blade and then extends his trephination a bit anteriorly to get as deep as he can and as close to Descemet's as possible. "I'm usually within 50 microns or so," he said. Then he uses a blunt lamellar instru- ment to try to dissect a tunnel from the periphery more centrally. He can then place the air cannula into this. "I think that the surgeon should abandon needles as injectors and get one of the designer cannulas," he said. "These are curved cannulas that direct the air posteriorly." When the air is injected, this sepa- rates Descemet's from the overlaying stroma. From there practitioners need to use a super sharp blade to let the air out of the bubble. Then De- scemet's membrane comes forward. "I then convert over to the vis- coelastic dissection to slowly inject the viscoelastic of my choice, which in this case would be Healon [Abbott Medical Optics, Santa Ana, Calif.] into that Descemet's space," Dr. Hol- land said. "I then use blunt scissors to remove the overlaying stroma." February 2011 May 2011 CORNEA continued on page 40 The eye on the left is one that underwent PK at the 7-year post-op mark; on the right, the same patient's DALK eye at just 18 months post-op, which appears almost identical Source: David D. Verdier, M.D.

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