Eyeworld

EW INTERNATIONAL 66 August 2018 losing some ground to this emerging technique. "There is an ongoing debate re- garding grafting for keratoconus. On the one hand, your head is telling you to use and keep the endotheli- um. But then the registry studies are telling us something different," Dr. Allan said. "Why is it that our head is telling us to use DALK? Because it avoids the endothelial rejection and accelerated endothelial cell loss that are seen in PK." Accelerated endothelial cell loss following PK is well documented in the literature. A systematic review based on 11 published studies revealed accelerated endothelial cell loss in eyes treated with PK versus DALK. It showed that DALK was not associated with endothelial immune graft rejection, which the investi- gators thought could simplify the long-term management of these eyes compared with PK. The study also demonstrated that DALK was equiv- alent to PK for CDVA. 1 Dr. Allan noted that while DALK could cause accelerated endothelial cell loss for up to 6 months after surgery, the rate of cell loss dramatically dropped after 6 months. These data, however, address outcomes in the short term. Know- ing more about the long-term course of corneal graft surgery is decisive. Registry evidence that included 4,834 eyes suggested that PK per- formed in eyes with keratoconus had a first graft survival rate of 17% at 23 years post-graft, indicating that young patients were likely to need at least one repeat graft during their lifetime. 2 For first grafts, the 10-year survival was 89%, the 20-year sur- vival 49%, and the 23-year survival was 17%. The 10-year survival of a second graft was 53%, and for third grafts, it was 33%. 3 "The Australian registry stud- ies are the most important piece of research in corneal medicine in the last 50 years," Dr. Allan said. "They guide everything we tell our patients in terms of prognosis and outcomes. They show us that between 20 and 30 years, most grafts run out of en- dothelial power. There is an acceler- ated failure in that time period for first grafts. Survival of second and third grafts is worse still. We usually graft keratoconus patients in their 20s, quite early in life, which is why a procedure with long life is what we are striving for." Long-term graft survival for the duration of a patient's lifetime was predicted with DALK, according to a study that used a joint regression model to describe long-term graft survival, involving 142 consecutive DALK surgeries and 142 matched PKs. The investigators predicted a median DALK graft survival of 47 years and a median PK graft survival of 17 years. 4 While DALK grafts that "take" survive a long time, how many grafts actually "take" in the first place? Researchers found that early graft survival (P<.001) and visual outcomes (P<.001) were significantly better for penetrating grafts, com- pared to DALK, for the same indi- cations. Graft failure at 3 years was 12% after DALK compared to less than 5% for PKs, according to data from more than 3,000 registry eyes. 5 This was largely corroborated by the outcomes of a U.K. trial that related the reason for DALK's higher overall failure rate compared to PK to early graft failures. The risk of graft failure for DALK was almost double that of PK (P=.02), with 19% of DALK failures occurring in the first 30 postoperative days, compared with only 2% of PKs. 6 "We had a high early failure rate for DALK at the time this graft regis- try data was collected, however, the technique has since then evolved," Dr. Allan said. "We've come on from doing deep stromal dissection to Descemet's baring techniques, which have become widespread. The key message here is that if you have good techniques, you have good results." Over time, better techniques appear to be yielding improved graft survival rates. Big bubble DALK is a Descemet's membrane baring technique that is currently credited with the highest degree of success, although it has not yet entirely replaced PK. This technique involves corneal trephination for 60–80% of its thickness. Air is injected into the deep stroma, causing a separation of the pre-Descemet's membrane from the overlying stroma, which is then bared and left intact, allowing the donor transplant to be placed on top, host endothelium intact. The idea is that by limiting the proce- dure to the stroma, there is a much lower threat to graft survival long term. According to a single surgeon series in 158 eyes with a follow-up of 4 years, the failure rate (eyes requir- ing regrafting) was just under 2% using the big bubble technique in keratoconus patients. DALK pro- vided stable long-term visual and refractive outcomes, with a reduced risk of graft rejection, postoperative complications, and late ECD, com- pared to standard PK. 7 by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer A corneal grafting specialist looks at short- and long-term outcomes with PK and DALK E arly graft survival in deep anterior lamellar kerato- plasty (DALK) for keratoco- nus patients is improving thanks to a number of smart variations in the technique that have been developed over time. Giving the keynote lecture at the 22nd ESCRS Winter Meet- ing, Bruce Allan, MD, Moorfields Hospital, London, U.K., discussed why penetrating keratoplasty (PK) is Grafting in keratoconus Graft 4 months out illustrating stromal rejection (20% of cases in DALK) Presentation spotlight Femto DALK host dissection Source: Bruce Allan, MD

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