EyeWorld India March 2018 Issue

the need to find reliable, reproduc- ible methods to get donor corneas to recipients who truly needed them in an expeditious manner. Since the days of Barraquer and keratophakia, that hurdle has been cleared, so now “it’s 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 lentic- ule 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, pub- lished a preliminary study involv- ing four emmetropic presbyopic patients who underwent the new PrEsbyopic Allogenic Refractive Lenticule (PEARL) inlay procedure. 4 This procedure involves taking a SMILE lenticule of a specified thickness and cutting it with a trephine to 1 mm in diameter. The button lenticule is then implanted into a femtosecond laser-created pocket centered over the pupil in the presbyopic patient’s nondomi- nant eye. The study found the pro- cedure to be safe and effective with all four patients reporting good uncorrected vision at near, interme- diate, and distance. “Overall, we found very good results for the patients,” Dr. Jacob said, adding that they’ve since also performed 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 intrastromal ring segments (CAIRS). As with synthetic intracorneal in- lays, the same complications can be associated with synthetic intrastro- mal ring segments. “I thought, why not use al- logenic 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 side as she would Intacs segments in a keratoconus patient. She has also used CAIRS as a single, almost fully circular, 330-degree segment. She has found that like Intacs, the allogenic segments result in good regularization of the corneal topography while also correcting some myopic refraction and im- proving uncorrected and spectacle- corrected distance visual acuity. It also spreads out biomechanical forces by flattening the cornea. For patients still at risk for keratoconus progression, she will perform CAIRS and then crosslink. “When you use allogenic tissue, the complications with synthetic materials are done away with, and therefore, a huge advantage is that you could use this in patients with corneas of any thickness unlike Intacs or other artificial segments where the cornea needs to have a certain minimum thickness in the zone of implantation,” she said. As for the preservation aspect of corneal lenticules for later use in procedures like these, Ganesh et al. described a technique of cryo- preservation in 2014 that seems to provide safe long-term storage. 5 From an inlay to an onlay Allotex is still in a research and engineering phase, with Dr. Muller saying they expect to start multi- centre clinical trials in Europe in the first quarter of 2018. “We haven’t focused on clinicals because we know it’s going to work. There’s too much data out there to show it works,” he said, citing published safety and/or ef- ficacy research for epikeratophakia, intracorneal inlays, and corneal allografts, including the positive outcomes of Dr. Jacob’s PEARL technique. “The key feature is with respect to safety, the jury is in. It’s hard to dispute 60+ years and hundreds of publications that show that hu- man allograft tissue works fine for creating [corneal] shapes,” Dr. Mul- ler said. “If you look at the more limited but compelling data that properly shaped human tissue gives A, 330-degree CAIRS segment seen implanted in keratoconic eye; B, preop and postop improvement seen in all parameters Source (all): Soosan Jacob, MD Is it the age - from page 45 46 EWAP REFRACTIVE March 2018