Eyeworld

EW FEATURE 68 Update on crosslinking • September 2017 AT A GLANCE • CXL has generated much interest since its U.S. approval for progres- sive keratoconus and ectasia. • Further studies of CXL are focusing on accelerated CXL and transepithelial CXL. • Research is underway abroad on the use of CXL with refractive surgery, and similar research is beginning in the U.S. • Results are mixed regarding CXL to treat infectious keratitis. by Vanessa Caceres EyeWorld Contributing Writer Where the U.S. market stands now, what approaches could be used in the future T he Food and Drug Admin- istration (FDA) approval of corneal crosslinking (CXL) last year for progressive keratoconus and ectasia brought an additional welcome treatment to the U.S. market, physi- cians said. "It's a very important approval," said Peter Hersh, MD, director of the Cornea and Laser Eye Institute, Teaneck, New Jersey; professor, Rut- gers Medical School, Newark, New Jersey; and visiting research collab- orator, Princeton University, Princ- eton, New Jersey. "Because of its unique ability to decrease progres- sion of KC and ectasia, we've seen widespread incorporation into oph- thalmic practice, especially among cornea surgeons. It's been adopted very quickly." Dr. Hersh was the medical monitor for the U.S. clinical trials for approval that were done by Avedro (Waltham, Massachusetts), the only company in the U.S. that currently offers FDA-approved CXL via its Photrexa Viscous, Photrexa, and KXL System. About 10,000 CXL treat- ments have been performed with the Avedro system since the FDA approval, said Rajesh Rajpal, MD, chief medical officer of Avedro, and founder of See Clearly Vision Group, Washington, D.C. area. Evolving treatment parameters Currently, there's an accelerat- ed CXL study underway that has completed enrollment and should be submitted to the FDA in the near future, said J. Bradley Randleman, MD, professor of clinical ophthal- mology, director of cornea, external disease, and refractive surgery, and medical director, USC Roski Eye In- stitute, Beverly Hills, California. The study uses the Avedro KXL protocol with 30 mW treatment. "The most basic process in the works is standard accelerated proto- cols, where total irradiance remains constant, but fluence increases and treatment time decreases," Dr. Randleman said. He contrasts this with higher irradiance accelerated protocols, where both fluence and total irradiation increase. "The concept is that accelerated proto- cols may not provide the same total treatment effect and depth as the standard protocol, so increasing flu- ence for a reduced time may allow for equal treatment efficacy but also maintain safety," he said. There is also research on the use of pulsed CXL. "The hypothesis is that the CXL reaction has multiple pathways, and one of these is oxy- gen-dependent," Dr. Hersh said. "It's thought that by using pulsed UV light during the dark phases, there will be replenishment of oxygen, and it will have a more robust cross- linking reaction." Another area under investi- gation is transepithelial CXL (or epithelium-on) and its relative effec- tiveness; the current FDA approval is for epi-off. At Dr. Hersh's practice, there is a physician-sponsored inves- tigational new drug study regarding the transepithelial technique, as well as the use of CXL and Intacs (Addition Technology, Lombard, Illinois). The latter study looks at the safety, efficacy, and timing of CXL and Intacs, either done the same day or performed sequentially over 3 months. These results will be available shortly. There's interest in the use of devices with a higher power along with epi-on treatments for shorter treatment duration of CXL; clinical trials in the U.S. for this are being planned, Dr. Rajpal said. Other areas under investigation include the use of oxygen to varying degrees with the CXL procedure and the use of other carriers beyond dextran, including HPMC, for ribo- flavin. Seeing clearer with CXL Imaging of corneal ectasia after LASIK CXL and refractive surgery One area with much interest for CXL is with refractive surgery. Avedro is planning its first U.S.- based trial for photorefractive intra- stromal corneal collagen CXL (PiXL) for low myopia, followed by one for presbyopia. With PiXL, myopic errors are treated with topical riboflavin and then cornea exposure to ultraviolet light delivered by Avedro's Mosaic device, which has a CE mark in Europe and approval from Health Canada but is not yet approved in the U.S. "Presbyopia is something most ophthalmologists would like to treat, and we have preliminary data to show it may be possible with PiXL," Dr. Rajpal said. The treatment of myopia with CXL is for about 1 to 1.5 D, or below what is typically treated with PRK or LASIK. The use of CXL for low myopia would treat in the center of the cornea, while for presbyopia it would treat the periphery. Crosslinking treatment Source: J. Bradley Randleman, MD

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