Eyeworld

EW GLAUCOMA 108 March 2017 by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer can highlight or stain the trabecu- lar meshwork, and it can pass into those distal aqueous veins and help highlight their location as well," he said. Dr. Seibold thinks that the next few years are likely to hold the promise of a clinically available method of outflow angiography. In referring to aqueous angiography, Dr. Seibold remarked, "As the field of MIGS continues to grow, in many cases targeting conventional outflow pathways, this type of imaging would be heavily used in surgical planning to identify who is a good candidate for an angle-based surgery but also where best to target outflow augmentation in a particular pa- tient. I think it holds great promise in providing another level of preci- sion and accuracy with angle-based MIGS procedures. They also hold significant diagnostic value for early diagnosed glaucoma patients, mon- itoring those patients throughout their lifetime, and monitoring their response to various treatments." Patient selection It pays to remain objective and discerning in this era of new and ex- citing options including sophisticat- ed imaging techniques. According to Kate Vinod, MD, assistant professor of ophthalmology, Icahn School of Medicine at Mount Sinai, New York, MIGS procedures are best-suited for patients with mild disease, which precludes its use in many of the patients whom she treats. Although several excellent technologies are second harmonic imaging micros- copy, but again, this is not currently being used in human patients yet," Dr. Seibold said. Using pigmentation in the anterior chamber intraoperatively can also help the surgeon visualize the trabecular meshwork and aids in stent placement. Dr. Seibold eluci- dated, "I can use areas of increased pigmentation in the trabecular meshwork, as a target for the loca- tions where I may want to implant an iStent or perform goniotomy. The areas of higher pigmentation can be an indicator of localized increased outflow, potentially overlying a patent collector channel or a large aqueous vein. This may give you a more pronounced pressure reduction by bypassing the trabecular mesh- work at those specific locations." Having different imaging modalities at your disposal allows you to choose the ones best suit- ed to your practice. Provocative gonioscopy and VisionBlue (trypan blue, Dutch Ophthalmic Research Center, Zuidland, The Netherlands) offer further imaging options, with reliable outcomes, Dr. Seibold said. "Provocative gonioscopy is a technique where the gonio lens is used to compress the eye to identify areas of blood reflux that might be more pronounced locally within the canal, again signifying areas of likely increased downstream outflow. These can help you target iStent implantation or goniotomy loca- tion as well. VisionBlue can be used intraoperatively, where it is injected into the anterior chamber, and this fact that the canal and the collector channels are embedded in the sclera makes it difficult to acquire high quality images as well," he told Eye- World in an interview on MIGS and imaging technologies. Anterior segment OCT is proba- bly the most commonly used clini- cal tool for imaging certain segments of the drainage system. It is used to help visualize outflow structures like the trabecular meshwork, Schlemm's canal, and the distal and intrascler- al outflow pathways. The imaging of these structures is important for devices such as the iStent (Glaukos, San Clemente, California), which creates a direct channel between the anterior chamber and Schlemm's canal. Aqueous angiography is a tech- nique that is still in a preclinical, re- search phase. It works similarly to a fluorescein angiogram, which is used to image retinal vasculature. How- ever, instead of injecting fluorescein into the venous system, it is injected into the anterior chamber, allowing an image to form out of the fluores- cein course that starts in the trabec- ular meshwork and Schlemm's canal and spreads further downstream to the episcleral venous system. "The only published studies that have implemented this technique thus far were in enucleated pig eyes. So, it is not ready for clinical use yet. But I think we are moving in that direction. Other imaging modalities like two-photon microscopy can be used to show very high resolution of outflow pathways using different modalities like autofluorescence and Experts discuss imaging techniques for aqueous outflow and their operative preferences M icroinvasive glauco- ma surgery (MIGS) is sweeping the glaucoma landscape, offering glaucoma specialists excellent new options for pressure relief in their mild and moderate glaucoma patients. Visualization of the eye's drainage system has taken on new relevance in light of this development, as an important deter- minant of stent feasibility within a particular patient's anatomy and for stent positioning, in both the prima- ry and secondary outflow pathways. Imaging According to Leonard Seibold, MD, assistant professor of ophthalmolo- gy, University of Colorado School of Medicine, Aurora, Colorado, imag- ing the aqueous outflow pathways in glaucoma patients is essential for patient selection for MIGS proce- dures. Although some imaging tech- niques are quite good, Dr. Seibold believes that challenges abound. "The extremely small size of the out- flow structures presents the biggest obstacle to imaging outflow. In addi- tion to the small size, most of these conventional outflow pathways are at many times only potential spaces that are often collapsed in vivo, making them easy to be missed us- ing a static imaging technique. The Imaging aqueous outflow and MIGS Intraoperative gonioscopy image before (left) and after (right) blood reflux into Schlemm's canal. In this lightly pigmented trabecular meshwork, blood in the canal highlights the targeted area for MIGS procedures. Source (all): Leonard Seibold, MD

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