Optical coherence tomography angiography (OCT-A) was used at the earliest stages of glaucoma to identify the characteristic patterns of different forms of the disease. OCT-A, a noninvasive technique that employs en face reconstruction of OCT combined with motion contrast processing to reveal perfused retinal vasculature, could enable doctors to diagnose glaucoma cases earlier than ever before and potentially slow down the progression of the disease. OCT-A image processing steps. (A) Contrast-stretched grayscale 4.5-mm OCT-A image of a healthy control. (B) Major blood vessel mask created using global thresholding. (C) Binary image after local adaptive thresholding with major blood vessels removed. (D) Color-coded perfused capillary density map. (E) Annular region of interest (ROI) centered at the optic nerve head. (F) Perfused capillary area within the annular ROI (in cyan) superimposed with (A). Courtesy of the Association for Research in Vision and Ophthalmology. Scientists from the New York Eye and Ear Infirmary of Mount Sinai (NYEE) and the Icahn School of Medicine at Mount Sinai used OCT-A to analyze 92 patients above the age of 50 between April and August of 2015. The patients were divided into three groups: those with primary open-angle glaucoma, with normal-tension glaucoma, and with no glaucoma. The researchers discovered that both types of glaucoma patients had fewer blood vessels, or less blood flow to the eyes compared to patients without glaucoma. Moreover, OCT-A revealed that patients with glaucoma had different patterns of defects in the blood flow of the most superficial layer of the retina, depending on the type of glaucoma they had. In high-pressure glaucoma, the pattern of blood flow loss closely matched the optic nerve fiber loss. In normal-tension glaucoma cases, the pattern of blood flow loss, while not significantly different from open-angle glaucoma, tended to be more diffuse. "This is the first time we have been able to identify certain characteristic patterns of blood flow that correspond to different types of glaucoma, which may allow us to identify certain forms of glaucoma in their early stages," said Richard Rosen, M.D. "The findings could lead to new therapeutic strategies to avoid progressive damage in glaucoma patients, and provide a new metric for monitoring early damage that eventually leads to vision loss." The researchers analyzed the images obtained with OCT-A using custom software that mapped the perfused optic nerve capillaries in each eye to reveal the patterns of the blood vessels feeding the optic nerve fiber layer. OCT-A is an easily interpretable, fast, reliable, noninvasive tool that permits visualization of perfused peripapillary capillaries, making it an attractive imaging modality for assessing glaucoma. This research is a first step in using OCT-A to investigate different patterns of glaucomatous changes in the peripapillary retina. Further research is necessary to determine the role of OCT-A in the detection, monitoring and characterization of glaucomatous nerve changes according to pathophysiological features. Future advancements in the technology may lead to OCT-A becoming a standardized imaging modality for the diagnosis and management of glaucoma. “Normal-tension glaucoma is often picked up late because it’s not recognized if patients don’t have high pressure, causing them to lose nerve fiber and blood supply before diagnosis,” said James C. Tsai, M.D. “This study points to vascular factors contributing to normal-tension glaucoma and we can use this to help identify ways to detect the disease earlier, and possibly prevent vision loss.” The research was published in Investigative Ophthalmology & Visual Science (doi: 10.1167/iovs.15-18945)