OCT 2013

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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56 EW CORNEA October 2013 Device focus Techniques, tools differ for DALK by Michelle Dalton EyeWorld Contributing Writer In the first step, the cornea is marked and an initial partial thickness trephination is made, followed by injection of air into the posterior stroma. A much more technically difficult procedure than PK, DALK is slowly gaining ground T he risk of graft failure in penetrating keratoplasty has led to some surgeons embracing deep anterior lamellar keratoplasty (DALK), where host endothelium is preserved. In general, DALK refers to techniques that remove all or a portion of the corneal stroma but leave an intact Descemet's membrane and endothelium. Despite the almost nonexistent rejection rate postDALK, only 1,855 graft procedures performed in 2012 in the U.S. were DALK. (There were 6,650 penetrating keratoplasty procedures for keratoconus in 2012, but only 805 DALK procedures for keratoconus.) The primary indications for DALK are keratoconus, anterior stromal dystrophies, and anterior stromal scars. And with the improved accessibility of corneal crosslinking for keratoconus, even fewer of the procedures may be done in the future, some say. Corneal surgeons in the Middle East and Asia are far more likely to use DALK than U.S.-based surgeons, said W. Barry Lee, MD, in private practice, Eye Consultants of Atlanta, and medical director, Georgia Eye Bank, Atlanta, noting the U.S. eye bank system is more developed. "By the time the tissue gets overseas, the endothelium is not as healthy," he said. "We can get grafts one or two days after the donor tissue is viable in the U.S." DALK "takes a lot longer than penetrating grafts," said Woodford A crescent blade is used to remove the superficial corneal layers (bulk keratectomy) van Meter, MD, professor of ophthalmology, Kentucky School of Medicine, Lexington. If surgeons can make a big bubble successfully, "it's a nice, esoteric procedure." The two main reasons Jacqueline Beltz, FRANZCO, corneal staff specialist, Royal Victorian Eye and Ear Hospital, Melbourne, Australia, performs the procedure are the predicted improved survival and the improved structural integrity "that can be achieved with some techniques of ALK." "My preference is to try for ALK in all patients with stromal disease, and reserve PK for those with full thickness disease. Planned PK makes up a very small percentage of my total number of corneal transplants." For cases of corneal stromal pathology, Massimo Busin, MD, Department of Ophthalmology, Villea Igea Hospital, Forlì, Italy, said, "My preferred techniques are superficial anterior lamellar keratoplasty (SALK), microkeratome enabled anterior lamellar keratoplasty (microkeratome enabled ALK) with cone collapse if the pathology is keratoconus, or mushroom keratoplasty." But in order to successfully perform DALK, surgical techniques (and the tools used to achieve success) make all the difference, these experts say. "DALK is a tough surgery to learn," Dr. Lee said. "It's technically challenging, and PK is quicker for most surgeons. As every U.S. surgeon is acutely aware, efficiency in the OR is more important than it ever has been with our current healthcare environment." A blunt dissector is used to separate Descemet's from the overlying stroma. Postoperatively, sutures hold the new tissue in place. Source (all): Barry Lee, MD Surgical steps Prof. Busin said the host pathology typically dictates his technique. "For superficial pathology, SALK is an effective technique that can be sutureless, allowing for rapid visual rehabilitation. For keratoconus I prefer microkeratome ALK, and find that a full thickness trephination of the residual host cornea, after the microkeratome pass effectively collapses the cone, allows for good visual outcomes. For full thickness disease, or corneas with extremely advanced keratoconus, a mushroom keratoplasty is effective," he said. For the latter, he uses a two-piece microkeratome prepared donor tissue with a 9.0 mm anterior "hat" and a 6.5 mm posterior "stem." Performing a big bubble "provides excellent results, but it's not reproducible in every case," Dr. Beltz said. "Manual techniques such as Melles' are reproducible, but may sacrifice some lines of visual acuity." She prefers to use a microkeratome over femtosecond lasers for her ALK procedures. Dr. Lee said Anwar's big bubble technique is his "go-to procedure" for keratoconus, although he does note his conversion rate to PK is about 15-20%, which he hopes to decrease. Dr. Lee uses a Hanna trephine (Moria, Antony, France) to a depth of about 350 microns; using a 30-gauge needle he introduces air into the posterior corneal stroma through the trephination site. "I remove the anterior stroma first (referred to as bulk keratectomy)," he said, using a crescent blade to remove the top 30–40% of the stroma. He uses Healon (Abbott Medical Optics, Santa Ana, Calif.) in the center of the cornea, "followed by a stab incision into the air pocket after placement of viscoelastic on the surface stroma to slow the release of air and decrease risk of perforation." Lastly, he'll use a blunt dissector to separate Descemet's from the overlying stroma followed by removal of stroma down to bare Descemet's membrane. Where his technique differs is in the creation of the big bubble, he continued. "I give myself two attempts to create the big bubble," he said. "I'll put the needle into the stroma after trephination, but if I'm not successful there, I'll perform my bulk keratectomy and replace the needle into the remaining posterior stromal tissue to attempt the big bubble again." Dr. Beltz uses a microkeratome enabled ALK with or without cone collapse as described by Prof. Busin if the corneal thickness is 380 microns or greater. "This technique has the advantage of reproducibility, and the anterior cap of a DSAEK donor can generally be used, hence allowing for two recipients from one donor tissue," she said. She reserves manual dissection, big bubble DALK, mushroom keratoplasty or PK for thin, steep, or irregular corneas or those with full thickness opacities. Because of the high quality donor tissue in Australia, she always has a PK quality tissue on standby "except for my microkeratome cases." For big bubble DALK, Dr. Beltz uses a 27-gauge needle. "[I] attempt to pass this with the bevel down as deeply as possible into the corneal stroma prior to injection of the big bubble. I have not had increased success with specially designed injection cannulas, although they

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