OSLI Retina

May/June 2013

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■ E X P E R I M E N T A L S C I E N C E ■ Evaluation of the Ability of a Photocoagulator to Rupture the Retinal Vein and Bruch's Membrane for Potential Vein Bypass in Retinal Vein Occlusion Ian L. McAllister, MD; Sarojini Vijayasekaran, PhD; Wei Xia, PhD; Dao-Yi Yu, MD, PhD INTRODUCTION BACKGROUND AND OBJECTIVE: To evaluate the laser power required to rupture both the retinal vein and Bruch's membrane in a porcine model using a new laser system for treatment of retinal vein occlusion. MATERIALS AND METHODS: The retina was treated in areas with and without an overlying vein. Sections through the laser sites were stained for light and transmission electron microscopy. The percentage of the laser sites with rupture of the retinal vein and Bruch's membrane, the degree of tissue damage, and the diameter of the rupture in Bruch's membrane were determined. RESULTS: The rate of vein rupture was 75% at 3 W, and rupture of Bruch's membrane was achieved at all powers tested. The mean diameter of the rupture in Bruch's membrane increased with laser power. CONCLUSION: The Integre Duo laser system (Ellex Medical Lasers, Adelaide, Australia) is capable of rupturing the retinal vein and Bruch's membrane at lower powers than prior laser systems. [Ophthalmic Surg Lasers Imaging Retina. 2013;44:268-273.] Central retinal vein occlusion (CRVO) is a major cause of visual morbidity and blindness in Australia and other developed countries for persons over the age of 40 years.1,2 The obstruction to retinal venous outflow is presumed to be due to a thrombus in the central retinal vein in or posterior to the lamina cribrosa region.3,4 Laser chorioretinal anastomosis, which creates an anastomosis between a choroidal and a retinal vein to bypass the obstruction in the central retinal vein, is the only proven treatment for CRVO aimed at its causal pathology.5 A range of pharmacologic agents targeting inflammatory, angiogenic, and vasopermeabilty molecules have been used to reduce macular edema caused by CRVO and improve vision; some have been proven successful in the short term, but repeated injections are required and the long-term effectiveness of these agents is unknown.6-11 The pathogenesis of macular edema in CRVO is multifactorial, likely including elevation in venous hydrostatic pressure, up-regulation of various cytokines induced by retinal hypoxia, and secondary inflammatory mediators. Intravitreal pharmacological agents address the elevation of cytokines but fail to address the elevated venous hydrostatic pressure, which may be important in the long term. We developed a technique of laser chorioretinal anastomosis using a dedicated K3 argon green laser (HGM, Salt Lake City, UT) to induce a bypass vessel between the retinal vein (away from the occlusion) and the choroidal vein beneath the retina through which blood flow can continue.12, 13 Trials in animal and human models determined the power density and laser From the Lions Eye Institute, Centre for Ophthalmology and Visual Science, The University of Western Australia, Perth, Australia (ILM, SV DY) and Ellex Medical Lasers Ltd., Adelaide, Australia (WX). Originally submitted November 15, 2011. Accepted for publication November 14, 2012. Grant support provided by the National Health and Medical Research Council of Australia and Ellex Medical Lasers. The study sponsors had no role in the study design; collection, analysis, and interpretation of data; writing the report; or the decision to submit for publication. Dr. Xia is an employee of Ellex Medical Lasers. The remaining authors have no financial or proprietary interest in the materials presented herein. Address correspondence to Prof. I. L. McAllister, Lions Eye Institute, Centre for Ophthalmology and Visual Science, the University of Western Australia, Nedlands, WA 6009, Australia; Email: ianmcallister@lei.org.au. doi: 10.3928/23258160-20130503-10 268 Ophthalmic Surgery, Lasers & Imaging Retina | Healio.com/OSLIRetina

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