OCT angiography and traditional angiography
OCT angiography is a promising new technique for visualizing retina and choroid vascular structures. Since 2015, papers on the OCT-angiographic features under various ophthalmic conditions have been widely published. Doctors Tan, Lim, and Sadda summarized these data and offered an description of the advantages of OCT angiography, fluorescein angiography and green indocyanine in the diagnosis of various ophthalmic conditions.
The OCT angiography procedure is based on the assumption that blood particles pass into the vessels of the blood, while the surrounding tissues remain motionless. With repeated still tissue shots the characteristics of the image remain unchanged from one frame to another. When objects shift, a coefficient of reflection varies over time and areas appear with low correlation of image characteristics from frame to frame. Blood flow through the vessels can be observed by examining variable amplitude or Doppler change.
OCT angiography is a simple, non-invasive approach that does not require coloring, which allows visualization of blood vessel structure and blood flow with a better resolution than conventional angiography. On the opposite, the conventional angiography procedure includes intravenous fluorescein or green indocyanine administration, which can be followed by allergic reactions up to anaphylactic shocks. The angiography with OCT is much quicker and easier, and can thus be done more frequently than the conventional technique.
Age-related macular degeneration
During age-related macular degeneration, choroidal neovascularization can be detected by angiography with fluorescein and green indocyanine and by angiography with OCT (Fig. 1). OCT angiography detects neovascularization foci in 64.4 percent of cases compared to fluorescence angiography, according to Innou M. On OCT angiograms, the choroidal neovascularization foci are located in the deep layers of the retina and in the choriocapillary layer (Fig. 1 B), while the vessels of the retina surface layers remain regular.
Foci of neovascularization
To date, the following options for choroidal neovascularization have been described:
- Foci with clear boundaries in the form of "lace" or "bicycle wheels with spokes";
- Long filiform linear vessels;
- Foci in the form of a "jellyfish": vessels grow in all directions from one main trunk;
- Foci in the form of a "sea surf": vessels grow from one main trunk mainly in one direction;
- Foci in the form of a ball;
- Foci with the shape of a "dead tree".
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