EyeWorld India December 2017 Issue

flap adhesion in these cases. 5–7 Anders Behndig, MD , pro- fessor and chief physician, Depart- ment of Clinical Sciences, head of the Department of Ophthal- mology, Umeå University, Umeå, Sweden, offered his perspective on LASIK Xtra, calling it a “promising method for preventing iatrogenic ectasia after LASIK.” “It has a theoretical rationale, and data are coming in supporting its clinical value. Furthermore, it appears the method may have op- tical benefits, [such as] the stabil- ity of the postoperative refraction, but it’s a bit early to say much about that,” Dr. Behndig said. Though he doesn’t have clini- cal experience with LASIK Xtra, Dr. Dupps said they’ve simulated it in computational models. The questions they hoped to answer were whether additional flattening of the cornea with crosslinking would cause over or under correc- tions that would require physi- cians to change their nomogram for LASIK and if it would have a protective effect against ectasia. Dr. Dupps said there was less than a quarter diopter difference in the simulation between the LASIK and the LASIK Xtra model, suggesting that mild crosslinking effects wouldn’t have an impact on nomograms. Protection against ectasia was a harder question to answer because it’s a rare condi- tion that would require long-term follow-up to assess the risk. “In the modeling exercise, we saw that if you stiffen that bed it does give the cornea more resistance to shape change,” he said, adding later that the most compelling argument for LASIK plus crosslinking he’s seen is by Kanellopoulos et al. in hyper- opic eyes. 6 This study showed the crosslinking LASIK group had less hyperopic regression over the year follow-up and better refractive outcomes. Correcting refractive error Another avenue for crosslinking is correcting refractive error. Pho- torefractive intrastromal crosslink- ing (PiXL) is in clinical trials with Avedro’s Mosaic system to provide topography-guided accelerated crosslinking to correct low levels of refractive error. “Our experience with PiXL for low myopia has been very posi- tive,” Dr. Elling said. “We have been performing epithelium-off PiXL since 2014, and since last year, we began offering epi-on treatments with supplemental oxygen. Our patients are very satisfied with the vision improve- ment, and the idea of a minimally invasive procedure is very appeal- ing. In our clinical studies, we had the possibility to show that we are able to reach a refractive change with PiXL.” Dr. Elling added that this technique hasn’t shown itself to be as precise as LASIK or PRK. 8 Referencing a company-spon- sored trial with 1-year follow- up, Dr. Elling noted statistically significant improvements in mean manifest sphere at all follow-up visits compared to baseline with a mean change of about 1 D. This reduction remained stable. “Given its noninvasive nature, PiXL presents a potential treat- ment option for patients with low myopia who require a less invasive refractive correction procedure than conventional laser vision cor- rection. In comparison to LASIK or PRK we have no tissue ablation. In the future, PiXL may give us the possibility … for refractive adjustments after cataract surgery, to treat irregular astigmatism, or even to do a touch-up after LASIK with thin residual stromal bed,” Dr. Elling said, adding that they are currently evaluating techniques to balance adequate epithelial disruption and postop comfort. Dr. Behndig said results with PiXL have shown stable and “suf- ficiently consistent” results. Going forward, both Drs. Behndig and Elling mentioned the possibility of PiXL for presbyopic correction. Dr. Dupps agreed that early trials of refractive crosslink- ing are encouraging, and he thinks that enhancing the predictability of refractive crosslinking is the next critical step in moving the concept forward. “By building on advances in crosslinking science to enhance and more tightly control the stiff- ening effect, other personalization tools such as corneal tomography, emerging biomechanical measure- ment technologies, and simula- tion-based planning tools can help leverage our predictive capabilities toward more personalized treat- ments,” he said. EWAP References 1. Roy AS, et al. Patient-specific compu- tational modeling of keratoconus progres- sion and differential responses to collagen cross-linking. Invest Ophthalmol Vis Sci. 2011;52:9174–87. 2. Seiler TG, et al. Customized corneal cross-linking: One-year results. Am J Oph- thalmol. 2016;166:14–21. 3. Cassagne M, et al. Customized topog- raphy-guided corneal collagen cross- linking for keratoconus. J Refract Surg. 2017;33:290–97. 4. Scarcelli G, et al. Biomechanical charac- terization of keratoconus corneas ex vivo with Brillouin microscopy. Invest Ophthal- mol Vis Sci. 2014;55:4490–5. 5. Tomita M. Combined laser in-situ ker- atomileusis and accelerated corneal crosslinking: an update. Curr Opin Ophthal- mol. 2016;27:304– 10. 6. Kanellopoulos AJ, et al. Topography- guided hyperopic LASIK with and without high irradiance collagen cross-linking: ini- tial comparative clinical findings in a con- tralateral eye study of 34 consecutive pa- tients. J Refract Surg. 2012;28:S837–40. 7. Seiler TG, et al. Superficial corneal crosslinking during laser in situ ker- atomileusis. J Cataract Refract Surg. 2015;41:2165–70. 8. Elling M, et al. Photorefractive intrastro- mal corneal crosslinking for the treatment of myopic refractive errors: Six-month in- terim findings. J Cataract Refract Surg. 2017;43:789–795. Editors’ note: Dr. Dupps has financial interests with Avedro, Op- toQuest (Cleveland), and Carl Zeiss Meditec (Jena, Germany). Dr. Elling has financial interests with Avedro. Avedro supports Dr. Behndig’s ongo- ing study on PiXL with an unrestrict- ed grant. Contact information Behndig: anders.behndig@umu.se Dupps: bjdupps@sbcglobal.net Elling: Matthias.Elling@kk-bochum.de Refractive opportunities – from page 47 December 2017 48 EWAP SECONDARY FEATURE