11, 4 including foveal avascular zone (FAZ) enlargement and irregularity, capillary drop out, and arteriolar abnormalities. Images were examined for classic features of diabetic retinopathy, such as microaneurysms (MAs) and RNV, as well as angiographic characteristics described by the ETDRS Report No. Specific features seen on OCT angiogram were then compared to FA features of the same area. The signal above the internal limiting membrane (ILM) was further segmented to isolate retinal neovascularization. Retinal angiogram was created by projecting the flow signal internal to the Bruch’s membrane in en face orientation. Flow was detected with the highly efficient split-spectrum amplitude decorrelation angiography (SSADA) algorithm 7, 8 and motion artifact was removed by 3D orthogonal registration and merging of 2 scans. Three dimensional (3D) OCT angiography scans were acquired over 6 × 6 mm regions using a commercially available 70 kHz OCT (RT-VUE XR, Optivue, Fremont, CA) with a scan pattern of 5 repeated B-scans at 216 raster positions and each B-scan consisting of 216 A-scans. They underwent comprehensive ophthalmic examination and FA. Patients were selected from the Retina Division of the Casey Eye Institute for the diagnosis of proliferative diabetic retinopathy, clear media, and the ability to fixate. This study describes features of diabetic retinopathy as seen on OCT angiography. 7 Applying this algorithm, an OCT angiogram in areas up to 6 × 6 mm area can be acquired in 3.5 seconds without intravenous injection. Our group has developed the split-spectrum amplitude decorrelation algorithm (SSADA) for efficiently detecting flow signals for angiography. Optical coherence tomography (OCT) angiography, a novel imaging technique that uses decorrelation between resampled images to detect flow to construct 2- and 3-dimensional images of blood flow within the eye, offers an alternative angiographic technique without some of the drawbacks of FA. 5 Also, a standard protocol FA acquires images over 10 minutes with repeated exposure to a very bright light source, 6 which can cause significant discomfort for patients. FA requires venipuncture and intravenous injection of a dye that has a moderate risk of nausea and a rare but well documented risk of anaphylaxis and death. While angiography provides valuable additional information compared to clinical examination or fundus photography, it is not part of the routine diabetic eye examination. 3, 4 Fluorescein angiography (FA) is also used to identify retinal neovascularization (RNV) in situations where clinical examination cannot detect RNV or distinguish from other anomalous appearing vessels on the retinal surface. Early Treatment of Diabetic Retinopathy Study (ETDRS) examined the fluorescein angiographic features of the posterior pole of patients with non-proliferative diabetic retinopathy and correlated the specific features with their risk of disease progression. 1 Detailed clinical examination for grading disease severity for risk of progression and vision loss is the standard of care 2, but ophthalmic angiography has played a critical role in understanding and care of the disease. Diabetic retinopathy is a microangiopathy that causes capillary occlusion, vascular hyperpermeability, and neovascularization in the retinal vasculature.
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