Optical Coherence Tomography Angiography (OCTA) is a non-invasive imaging technique that provides detailed, depth-resolved images of blood flow in the retina and choroid. Building on the foundation of Optical Coherence Tomography (OCT), OCTA offers superior resolution and detail compared to older imaging methods like fluorescein angiography (FA). The development of OCTA has been driven by advancements in OCT technology, including higher imaging speeds and improved signal processing techniques. This review covers the historical development of OCTA, its underlying principles, and its applications in various ophthalmic conditions. Key aspects of OCTA include: 1. **Signal Processing and Image Generation**: OCTA detects motion contrast by repeatedly imaging the same retinal location, comparing changes between successive B-scans. The interscan time is crucial for balancing sensitivity to motion and the impact of bulk eye motion. 2. **Advantages and Limitations**: OCTA provides high-quality, well-defined images of microvasculature without the need for exogenous contrast agents. It can be performed rapidly and is useful for assessing retinal vascular diseases. However, it has limitations in assessing vascular permeability and leakage, and its results can be influenced by instrument-specific factors. 3. ** Visualization Methods**: OCTA data can be visualized using en face projections, which show flow information for individual retinal layers, or cross-sectional B-scans, which provide more precise depth information. En face projections are simpler to interpret but can be prone to segmentation errors, especially in pathological cases. 4. **Commercialization**: The commercialization of OCTA has been significant, with multiple instruments now available for clinical use. These instruments vary in their acquisition protocols, signal processing algorithms, and display methods, leading to differences in performance and interpretation. Overall, OCTA is a powerful tool for visualizing and analyzing retinal microvasculature, offering valuable insights into disease pathogenesis and treatment response. However, its interpretation requires careful consideration of the underlying imaging principles and potential artifacts.Optical Coherence Tomography Angiography (OCTA) is a non-invasive imaging technique that provides detailed, depth-resolved images of blood flow in the retina and choroid. Building on the foundation of Optical Coherence Tomography (OCT), OCTA offers superior resolution and detail compared to older imaging methods like fluorescein angiography (FA). The development of OCTA has been driven by advancements in OCT technology, including higher imaging speeds and improved signal processing techniques. This review covers the historical development of OCTA, its underlying principles, and its applications in various ophthalmic conditions. Key aspects of OCTA include: 1. **Signal Processing and Image Generation**: OCTA detects motion contrast by repeatedly imaging the same retinal location, comparing changes between successive B-scans. The interscan time is crucial for balancing sensitivity to motion and the impact of bulk eye motion. 2. **Advantages and Limitations**: OCTA provides high-quality, well-defined images of microvasculature without the need for exogenous contrast agents. It can be performed rapidly and is useful for assessing retinal vascular diseases. However, it has limitations in assessing vascular permeability and leakage, and its results can be influenced by instrument-specific factors. 3. ** Visualization Methods**: OCTA data can be visualized using en face projections, which show flow information for individual retinal layers, or cross-sectional B-scans, which provide more precise depth information. En face projections are simpler to interpret but can be prone to segmentation errors, especially in pathological cases. 4. **Commercialization**: The commercialization of OCTA has been significant, with multiple instruments now available for clinical use. These instruments vary in their acquisition protocols, signal processing algorithms, and display methods, leading to differences in performance and interpretation. Overall, OCTA is a powerful tool for visualizing and analyzing retinal microvasculature, offering valuable insights into disease pathogenesis and treatment response. However, its interpretation requires careful consideration of the underlying imaging principles and potential artifacts.