EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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54 EWINTERNATIONAL August 2012 International outlook At the heart of corneal biomechanics: tomography and a study group by Matt Young EyeWorld Contributing Writer Brazil-based group shines spotlight on technology and methods to prevent ectasia T he corneal biomechanical response is a critical variable in achieving predictable refractive surgical out- comes. The challenge has always been determining which characteristics of the cornea differentiate normal from atypical. LASIK surgeons have understood the importance of this since the early days of refractive surgery. With the emergence of cataract surgery as a de facto refractive procedure, anterior segment surgeons must now also assess the cornea to plan astigmatic correction. Renato Ambrosio Jr., M.D., and Bruno M. Fontes, M.D., have extensively studied corneal topogra- phy, tomography, and hysteresis in an effort to better understand and predict the corneal response to refractive surgery. John Vukich, M.D., international editor W hen it comes to corneal biomechanics, there's no more in- tense research going on than in the Rio de Janeiro Corneal Tomography and Biomechanics Study Group. In its field, the group has been heralded for pushing forward new thinking, which ultimately leads to better corneal surgery products, safer ophthalmic surgery, and happier patients. Members of the group have won recent awards from ASCRS, ESCRS, and ISRS for their work on corneal thickness profiles, tomography, corneal biomechanics, and enhanced screening capabilities. Ultimately, a considerable amount of what we currently under- stand about corneal biomechanics— and some controversy, too—begins with this small group in Brazil. Early beginnings Just as Renato Ambrosio Jr., M.D., Visare Personal Laser, Clinica Oftal- mologica Dr. Renato Ambrosio Jr., Rio de Janeiro, was finishing medical school, his father passed away. But tucked away on VHS tapes were some important lessons for the young Dr. Ambrosio. "I saw a video that he recorded," said Dr. Ambrosio, scientific coordi- nator of the study group. "He had recorded a course on RK in 1982. [The lesson involved] the cornea having important characteristics when one is performing RK—for instance, thickness. Even in those early times, they were considering that, and those ideas really influ- enced me over the years." Family ties are what brought Dr. Ambrosio to the world of corneal biomechanics. But it was his whole- hearted passion for the subject that "There is low hysteresis for both strong and fragile corneas, for differ- ent reasons," said Dr. Fontes, in pri- vate practice, Rio de Janeiro. "But there is a significant overlap." Meanwhile, the group was find- ing new parameters yielding more insights into what differentiates healthy and normal corneas. "We are still working to improve sensitivity and specificity," Dr. Fontes said. "What we need right now for refractive surgery evolution is a trustworthy way to measure corneal strength to detect pre-opera- tively patients who are at higher risk to develop post-surgical ectasia." Additionally, Dr. Fontes said it's important to be able to measure in- dividual corneal stress to modulate laser energy to treat each patient in- dividually. Strong corneas, for example, might need more laser energy to shape them correctly. Fragile corneas might need less energy. "The biomechanical frontier is the next step to the refractive sur- gery evolution," Dr. Fontes said. "We need it not only to screen for ectasia risk but to develop an individual nomogram to modulate laser energy for each patient." Further, the group has acted like Ectasia after LASIK with unrecognized risk factors based on standard screening (front surface topography and CCT) led him to found the study group in 2005. Bruno M. Fontes, M.D., in need of a subject for his Ph.D. thesis, soon joined the group, as did others. The group's work initially fo- cused on generating tomographic data for both healthy and kerato- conic patients in the Brazilian popu- lation. It also generated valuable information regarding corneal hysteresis. With a series of new paper pub- Enhanced screening Source (all): Renato Ambrosio Jr., M.D. lications, the group was finding sta- tistically different values for healthy and keratoconus groups. Impor- tantly, it found that as people get older, lower values of corneal hysteresis appear. a watchdog, ensuring that corneal analysis tools like the Ectasia Risk Score System (ERSS) receive appro- priate discussion and deliberation. For instance, Dr. Ambrosio and Michael W. Belin, M.D., published an editorial on the ERSS in the Journal of Refractive Surgery in April 2010, noting that 8% of LASIK cases develop ectasia despite a low ERSS score, and there is "a false positive rate as high as 35% if a relatively young population is evaluated." Tomography versus topography When the study group started, Dr. Ambrosio didn't have tomography capability. "I knew I needed it, but I was doing LASIK without it," Dr. Ambrosio said. Yet he desired some- thing that went beyond current refractive screening for LASIK candidates. "I saw many cases of ectasia that didn't have an explanation," Dr. Ambrosio said. Keratoconus itself is a common disease, Dr. Ambrosio said.