Eyeworld

EW REFRACTIVE 64 December 2017 by Liz Hillman EyeWorld Staff Writer time to look to using donor corneal tissue for more advanced refractive procedures," Dr. Negrin said. From SMILE to PEARL and beyond The lenticule removed in SMILE procedures, which might otherwise be discarded, is being used by some to provide hyperopic or presbyopic treatments and may even have ap- plications for keratoconus patients. Pradhan et al. in 2013 described endokeratophakia where the lenti- cule from a myopic SMILE procedure was implanted in another patient to correct hyperopia. 3 Earlier this year, Soosan Jacob, MD, Dr. Agarwal's Eye Hospital, Chennai, India, published a preliminary study involving four emmetropic presby- opic patients who underwent the new PrEsbyopic Allogenic Refractive Lenticule (PEARL) inlay procedure. 4 This procedure involves taking a SMILE lenticule of a specified thick- ness and cutting it with a trephine to 1 mm in diameter. The button lenticule is then implanted into a femtosecond laser-created pock- et centered over the pupil in the presbyopic patient's non-dominant eye. The study found the procedure to be safe and effective with all four patients reporting good uncorrected vision at near, intermediate, and distance. "Overall, we found very good re- sults for the patients," Dr. Jacob said, adding that they've since also per- formed myopic SMILE on patients and then used their own lenticule for autogenic PEARL. In addition to PEARL, Dr. Jacob at the 2017 ASCRS•ASOA Sympo- sium & Congress described a new technique using linear stromal tissue segments similar to Intacs (Addition Technology, Lombard, Illinois) to create corneal allogenic intrastro- mal ring segments (CAIRS). As with synthetic intracorneal inlays, the same complications can be associat- ed with synthetic intrastromal ring segments. "I thought, why not use allo- genic segments made from donor cornea?" Dr. Jacob said, explaining that she uses a double-bladed tre- phine to punch out a full-thickness, circular segment of corneal tissue from donor cornea and then cuts it in two, implanting them on either New procedures using allogenic tissue for refractive correction T he idea of using allogenic— 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 precision needed to get a good refractive re- sult," 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 Is it the age of allogenics? A: PEARL lenticule prepared; B: PEARL lenticule inserted under a cap in the non-dominant eye; C: postop slit lamp appearance; D: postop Orbscan showing central area of hyperprolateness continued on page 66 and experience accurately reshaping 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 presby- opia 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, Massa- chusetts), 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 procedures available in the U.S. Options that have received FDA approval include multifocal, trifocal, and extended depth of focus IOLs and two intra- corneal inlays (KAMRA, AcuFocus, Irvine, California, and Raindrop, Revision Optics, Lake Forest, Cali- fornia); 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 premi- um IOL, and currently approved intracorneal inlays, which target this pre-cataract market, are foreign bodies in the eye. They are, however, designed with nutrient and oxygen diffusion in mind. Corneal allografts, in contrast to synthetic materials, are 100% neutral "Once you put this allogenic material in the cornea, it's repopu- lated by the patient's own kerato- cytes, and it becomes part of the cornea," Dr. Muller said. Anne Negrin, MD, a practicing ophthalmologist and TV medical 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 allografts for refractive purposes can use other parts of the cornea. "We don't take away any cor- neas 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 refrac- tive correction was due to the need to find reliable, reproducible meth- ods to get donor corneas to recipi- ents who truly needed them in an expeditious manner. Since the days of Barraquer and keratophakia, that hurdle has been cleared, so now "it's

• Blank Page
• Blank Page (1)