EyeWorld Asia-Pacific March 2018 Issue

Is it the age of allogenics? by Liz Hillman EyeWorld Staff Writer New procedures using allogenic tissue for refractive correction T he idea of using allogen- ic—human donor—tissue for refractive surgery goes back to Jose Barraquer, MD , who published his idea of epikeratophakia in 1949. 1 Even in the 1980s when there was a resur- gence of interest in putting a donor cornea on an aphakic patient’s own cornea with promising results, it did not go mainstream. 2 This was most likely due to the success of laser refractive surgery. As David Muller, PhD , Boston, put it, the surgical technique and technology at the time were not refined enough to maximize outcomes or open up the possibility for other refractive procedures. “The problem that plagued it all through the 1980s is that there was no real metrology to measure tissue thickness and tissue size. There was also no good mechanical way … to cut the tissue with the preci- sion needed to get a good refractive result,” Dr. Muller said. Fast forward to present day and Dr. Muller said we not only have accurate metrology for the precise measure of tiny tissues, but we have 20-plus years of laser development and experience accurately reshap- ing corneas. The availability of corneal tis- sue—either from donors or from tis- sue removed during other refractive procedures—and the benefit of bio- compatibility makes allogenic tissue implants—allografts—an attractive option for refractive procedures like correction of hyperopia or presbyo- pia and even has applications for keratoconus. Allogenic vs. synthetic Dr. Muller, well-known in the ophthalmic innovation space for his work with the excimer laser and Summit Technology (acquired by Alcon, Fort Worth, Texas, in 2000) and later Avedro (Waltham, Mas- sachusetts), in 2014 founded Allotex (Zurich, Switzerland, and Boston), a company working on bring allogen- ic inlays and onlays for correction of presbyopia to the market. There are already several surgi- cal presbyopia-correcting proce- dures available in the U.S. Options that have received U.S. Food and Drug Administration (FDA) ap- proval include multifocal, trifo- cal, and extended depth of focus IOLs and two intracorneal inlays (KAMRA, AcuFocus, Irvine, Califor- nia, and Raindrop, Revision Optics, Lake Forest, California); more are in development or are approved elsewhere. And there is monovision LASIK. Dr. Muller said presbyopia almost always affects patients well before they develop a cataract and might be a candidate for a pre- mium IOL, and currently approved intracorneal inlays, which target this pre-cataract market, are foreign bodies in the eye. They are, how- ever, designed with nutrient and oxygen diffusion in mind. Corneal allografts, in contrast to synthetic materials, are 100% neutral “Once you put this allo- genic material in the cornea, it’s repopulated by the patient’s own keratocytes, and it becomes part of the cornea,” Dr. Muller said. Anne Negrin, MD , a practic- ing ophthalmologist and TV medi- cal contributor in the greater New York area, said that while she hasn’t personally used synthetic inlays, she understands that foreign body complications could occur. “These inlays aren’t real corneal tissue, and they tend to behave as though they have a mind of their own, making refractive results less than optimal or simply not stable,” Dr. Negrin said. From a donor cornea stand- point, Dr. Muller said that the U.S. has an ample supply of corneas, and surgeons performing corneal transplants are mostly interested in endothelial cells, while corneal al- lografts for refractive purposes can use other parts of the cornea. “We don’t take away any corne- as that can be used for transplants … no one’s vision is prejudiced because we took a cornea,” he said. What’s more, he said the amount of donor corneas that can be accepted is expanded for this purpose as age, endothelial cell quality, and the like are less of an issue because “we’re using the heart of the stroma for our process.” Others aren’t using donor corneas, per se, for allografts but are using the lenticules from small inci- sion lenticule extraction (SMILE). Echoing similar thoughts to Dr. Muller’s, Dr. Negrin said she thinks the main reason why human corneal donor tissue was not used for refractive correction was due to A, PEARL lenticule prepared; B, PEARL lenticule inserted under a cap in the nondomi- nant eye; C, postop slit lamp appearance; D, postop Orbscan showing central area of hyperprolateness continued on page 46 EWAP REFRACTIVE 45 March 2018