Eyeworld

EW CORNEA 94 April 2016 by Matt Young and Gloria Gamat EyeWorld Contributing Writers Physicians report on new developments at the 2015 AAO meeting W hile riboflavin-mediat- ed ultraviolet cross- linking has turned into an effective method of slowing down the progression of structural corneal disorders like keratoco- nus and post-LASIK ectasia, one limitation that keeps challenging ophthalmic surgeons is the need for epithelial debridement to maximize the diffusion rate of riboflavin into the stroma. At the 2015 American Academy of Ophthalmology (AAO) annual meeting, Edward Manche, MD, director of cornea and refractive sur- gery, Stanford Eye Laser Center, and professor of ophthalmology, Stan- ford University School of Medicine, Palo Alto, California, and David Myung, MD, PhD, ophthalmology faculty, VA Palo Alto Health Care System, and ophthalmology faculty, Stanford University, reported on the development of a novel vacuum- based delivery system that facilitates delivery of therapeutic doses of riboflavin to the cornea through an intact epithelium. Variability in transepithelial crosslinking Epithelial debridement is known for its painful recovery period and risk "In children, it may be desirable to minimize discomfort and accept a less than maximum efficacy as the procedure may be repeated later on; in contrast, in very thin corneas, it may be an option to use an aggres- sive protocol to maximize efficacy even if the epithelium sloughs off postoperatively in order to have the epithelium as a protective spacer to the endothelium," they reported. Meanwhile, in a study using rabbit and human cadaver corneas, Vinciguerra and colleagues 2 com- pared the changes with regard to tissue penetration and distribution of riboflavin and the stress-strain following different crosslinking pro- tocols (iontophoresis, standard and transepithelial). "A secondary goal of our study was to evaluate if iontophoresis crosslinking is capable of inducing a good penetration of riboflavin and increase corneal rigidity, differently from transepithelial crosslinking," reported Vinciguerra and colleagues in BioMed Research International. Transepithelial corneal collagen crosslinking, noted the research team, is meant not only to reduce the risk of infections but also allow for faster vision recovery and short- en the period of treatment, without compromising the efficacy of the procedure. "We observed that iontophore- sis induced acceptable penetration of riboflavin in all corneal layers, which is the basis for efficient of infection and scarring. This has led experts to look into potential new ways of delivering therapeutic doses of riboflavin while keeping the epithelium intact in order to overcome such problems. Delivering riboflavin via the transepithelial route using ultrasound or iontopho- resis has been investigated, but with conflicting—and sometimes contro- versial—results. In a study that evaluated the impact of different methods of transepithelial riboflavin delivery through the corneal epithelium in terms of pain and epithelial integrity during the early postoperative peri- od, Taneri and colleagues 1 reported in the Journal of Ophthalmology that it may be impossible to have suffi- cient riboflavin penetration without disrupting the epithelium, unless a compromise between efficacy and epithelial integrity is found. "The optimal approach for tran- sepithelial crosslinking must mini- mize the impact on the corneal epi- thelium while permitting a sufficient amount of riboflavin to diffuse into the stromal tissue where crosslinking occurs," explained Suphi Taneri, MD, Center for Refractive Surgery, Eye Department at St. Franziskus Hospital, Muenster, Germany. Results of their study revealed a variability in postoperative recovery following transepithelial crosslink- ing with different treatment regi- mens. crosslinking, even with an intact epithelium," said Paolo Vinciguerra, MD, medical director, Vincieye Eye Clinic, Milan, and pro- fessor of ophthalmology, University of Milan. "The effective presence of ribo- flavin together with ultraviolet-A produced, as measured in our stress- strain measurements, a significant increase in corneal stiffness in the iontophoresis crosslinking group compared to controls, therefore partly confirming previous reports," he said. "Even if more studies are needed to evaluate safety and efficacy, cor- neal crosslinking with iontophoresis is potentially a valid alternative to standard crosslinking in improving corneal biomechanical properties and reducing postoperative pa- tient pain, risk of infection, and treatment time," the research team concluded. How a novel vacuum- based device fits into the transepithelial crosslinking picture "The delivery system is a hand- held unit and a vacuum pump that induces negative pressure," Dr. Manche said. "It includes a fenestrated hand- held unit fabricated via high resolu- tion stereolithography that creates a Vacuum-based system delivers riboflavin through intact corneal epithelium Vacuum-mediated transepithelial delivery of riboflavin to the cornea Source: Edward Manche, MD Epithelium-on Epithelium-off Epithelium-on vacuum-based delivery Presentation spotlight continued on page 96

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