OCTA uses motion contrast between cross-sectional OCT scans (B-frames) to differentiate blood flow from static tissue, enabling imaging of vascular anatomy.
[18] This form of OCT requires a very high sampling density in order to achieve the resolution needed to detect the tiny capillaries found in the retina.
[18][19] This has allowed OCTA to obtain detailed images of retinal vasculature in the human retina[20] and become widely used clinically to diagnose a variety of eye diseases, such as age related macular degeneration (AMD),[21] diabetic retinopathy (DR),[22][23] artery and vein occlusions, and glaucoma.
[27] In diabetic retinopathy (DR), OCTA was shown to resolve previously established markers of severe disease (i.e., vitreous proliferation).
[32][33] OCTA detects moving particles (red blood cells) by comparing sequential B-scans at the same cross-sectional location.
This is where SSADA proves to be very advantageous as it is able to greatly improve SNR by averaging the decorrelation across the number of B-scans, making the microvasculature of the retina visible.
Still, Doppler techniques were fundamentally limited by bulk eye motion artefacts, especially as longer scan times became important for increasing sensitivity.
Systems also began to measure the variance and power of the Doppler phase between successive A-mode and B-mode scans; later it was shown that successive B-mode scans must be corrected for motion and the phase variance data must be thresholded to remove bulk eye motion distortion.
[43] The most common angiographic techniques were fluorescein (FA) or indocyanine green angiography (ICGA), which both involve the use of an injectable dye.