الفهرس 
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Abstract
SUMMARY
Diabetic retinopathy is one of the most important challenges that faces the diabetic patients, simply it is a microangiopathy of the retina which leads to impairment of visual abilities if neglected, consists of many factors such as vascular walls changes and alterations in blood physiological criteria. These factors leads to capillary occlusion and so to fluid leakage and retinal ischemia.(1)
According to the ETDRS, It is divided into Non-proliferative (mild-moderate-severe) and proliferative retinopathy according to the severity of changes occurs within the retina and the degree of ischemia and new vessels proliferations.(1)
To compensate the ischemia resulting from micro-capillary occlusions and hypoperfusion that invade a large portion of the retinal tissue, vascular endothelial growth factor (VEGF) and other mediators take the upper hand and accelerate the new vessels formation process and this leads to proliferative diabetic retinopathy (PDR).
Consequences of neglected PDR aren’t favourable, usually show vitreous haemorrhage, tractional retinal detachment and neovascular glaucoma. (1)
FFA is considered the gold standard clinical imaging modality for evaluating retinal and choroidal vascular pathologies that based on the optical principle of fluorescence by injection of dye and exciting it with cobalt blue light.(6, 4)
FFA has advantages such as wider imaging area of the retinal and choroidal vasculature, also it is less liable to show artifacts.despite this, it shows weak points regarding it is time consuming, invasive technique, and susceptibility of allergic reactions.(6)
Optical coherence tomography angiography is a recent, non-invasive imaging technique of the retinal and choroidal microvasculature, adopts a highly-detailed, depth resolved and three-dimensional display facilitates quantitative and qualitative assessment of the capillary plexuses.(6, 11)
It is based on the principle of Flow Motion detection that detects the RBCs movement inside the retinal vessels with no need for dye injection, OCTA shows marked advantages such as Fast acquisition time and being non –invasive, but it still has some limitations such as limited imaging field specially in the available softwares in the market and susceptibility to artifacts.(11)
Motion, projection, segmentation and shadowing artifacts are examples of the common OCTA imaging artifacts.(43, 47)
OCTA plays an important role in diabetic retinopathy, especially that it highlights changes in the retinal microcirculation in diabetic patients before the clinically visible retinopathy develops.(78)
OCTA shows perfect results in close observation of some DR changes such as capillary non-perfusion, ischemia and neovascularization.(40, 45)
Conventional OCTA is superior to FFA in assessment of clinically unsuspected NVs especially in the central field of the retina, however FFA wins in evaluation of these NVs in the peripheral field due to broad surface area of image acquisition.(43, 47)