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EW GLAUCOMA 84 February 2017 by Maxine Lipner EyeWorld Senior Contributing Writer Rosen said, adding that this goes along with the vascular theory that may be an important component in many patients. Clinically, this may give prac- titioners an opportunity to inter- vene sooner in those who have risk factors but by other measures look normal. "We may be able to pick up on a patient who is starting to develop glaucoma in the early stages before we see the loss of the nerve fiber layer, before we see function- al changes," Dr. Rosen said. "This opens up the possibility of interven- ing earlier." He views this as potentially significant because it is something that clinicians weren't able to image before. However, this will have to be validated by larger groups who follow more glaucoma patients. A particularly exciting part of OCT angiography is its potential, Dr. Rosen thinks. Fluorescein angiog- raphy, while a great tool that has been invaluable in understanding glaucoma and retinal disease, is in- vasive, he pointed out, adding that it's not done for a lot of diseases on a regular basis. "This is noninvasive, painless, and quick," he said. "But the real added feature is it's quan- titative, so it allows us to analyze these patterns that previously we didn't have an easy way to do." Patients will find this quantitative aspect reassuring, he thinks. "When we have numbers, we have a greater sense of reliability on the data that we're looking at," Dr. Rosen said. This makes it possible to start look- ing at number ranges and develop a normative database, something his lab is currently working on. EW Reference 1. Scripsema NK, et al. Optical coherence tomography angiography analysis of perfused peripapillary capillaries in primary open-angle glaucoma and normal-tension glaucoma. Invest Ophthalmol Vis Sci. 2016;57:OCT611– OCT620. Editors' note: Dr. Rosen has financial interests with Optovue (Fremont, California). Contact information Rosen: RRosen@NYEE.EDU elevation in pressure over a long pe- riod of time. This is akin to the way that water will wear down earth, Dr. Rosen explained. While pressure elevated more than 24 mm Hg is a known risk factor for glaucoma, there are some patients who don't fall in that elevated range who still lose visual field and nerve fiber. "We've always suspected that, and there have been a lot of studies over the years that have shown there is a strong component of vascular compromise that is responsible," he said. "What we found was that both those who were considered to be normal-ten- sion and those who were high-ten- sion glaucoma patients had reduced capillaries compared to the normal group that we looked at." Investiga- tors also noticed that the loss of the nerve fiber layer correlated closer in the high-tension glaucoma patients, with less of a correlation in those with normal-tension glaucoma. "In fact, they seemed to have a little more diffuse loss of the capillaries compared to the loss of the nerve fiber, which suggests that there may be some loss in the capillaries that precedes the loss of the fibers," Dr. raphy. "This is a revolution in terms of our ability to distinguish early changes that possibly precede the loss of thickness of the nerve fiber layer," he said. Looking for patterns Investigators in this study set out to see if they could find any early pat- terns. Included here were 92 patients over age 50. Patients were placed into one of three groups: normal, those with high-pressure glaucoma, and those with normal-tension glau- coma. Then OCT angiography was performed. Investigators found some dis- tinct things. "We saw that the glau- coma patients have a loss of these (radial peripapillary) capillaries, which you would expect once you lose the structures around it," Dr. Rosen said. "The question is like the chicken and egg: What goes first? Is it the pressure or is it the circula- tion?" Investigators think that the high pressure system makes a dif- ference in terms of pushing on the delicate nerve axons and blocking the flow of nutrients within those nerve fibers, he said. The theory is the damages result from a slight OCT angiography identifies new patterns in early glaucoma I magine being able to spot glau- coma patients headed for vision loss based on something besides IOP alone. Investigators in a study published in Investigative Ophthalmology & Visual Science 1 were able to use optical coherence tomog- raphy (OCT) angiography to hone in on the unique patterns of blood flow that could help to identify glaucoma at its earliest stages, explained co-au- thor Richard Rosen, MD, director of ophthalmology research, and chief of the retina service, New York Eye and Ear Infirmary of Mt. Sinai, New York. Eyeing OCT angiography "Glaucoma is generally asymptom- atic until very advanced stages, and there is no real reversal," Dr. Rosen said. "The earlier that physicians detect the disease, the better they'll be able to decrease the damage that ultimately occurs." One of the major problems that practitioners have faced is they would look at the pressure and consider optic nerve changes, which in the case of normal-pressure patients were already fairly advanced by the time these had manifested, Dr. Rosen ex- plained. "Often, because you have a group of patients who have normal pressures, you don't suspect dam- age," he said, adding the visual fields don't reflect damage until fairly late in the course of the disease because there is quite a bit of redundancy within the system. As a result, before there is actual functional change, the patient has already lost a lot of nerve tissue. However, more recently with OCT, it has been possible to detect loss within the nerve fiber layer at a micron level. "OCT angiography is an extension of the latest OCT tech- nology, and has given us the unique ability to image a layer of capillaries called the radial peripapillary capil- laries," Dr. Rosen said. "They are the capillaries that feed the nerve fiber layer." This is something that no one had been able to image clinical- ly before the advent of OCT angiog- Going with the peripapillary capillary flow Research highlight Comparisons of 4.5 mm OCT-A images and color-coded perfused capillary density maps in a normal, severe POAG, and severe NTG patient. Column 1: Grayscale OCT-A images generated using SSADA algorithm. Column 2: Thresholded binary images contain only the perfused capillaries after the removal of major blood vessels. Column 3: Corresponding color-coded perfused capillary density maps. Column 4: Superimposed image of the color maps and the inverted OCT-A images. All images show the temporal peripapillary region on the left. Source: Richard Rosen, MD

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