What is the role of indocyanine green (ICG) angiography in the workup of choroidal neovascularization (CNV)?

Updated: Jan 07, 2019
  • Author: Lihteh Wu, MD; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Answer

Indocyanine green (ICG) is a water-soluble tricarbocyanine dye that contains 5% sodium iodide; it rapidly binds almost completely to globulins after intravenous injection. ICG has a peak absorption and fluorescence in the near infrared range. This allows visualization of choroidal pathology through overlying serosanguineous fluid, pigment, or a thin layer of hemorrhage that usually blocks visualization during FA. Because ICG is bound tightly to the plasma proteins, less dye escapes from the choroidal circulation, allowing better definition of choroidal vasculature.

Three types of ICG patterns that are assumed to represent CNV may be imaged. A hot spot is a well-defined focal hyperfluorescent area that is less than one disc area in size. Hot spots usually fluoresce early. A plaque refers to a hyperfluorescent lesion that is larger than one disc area in size. A plaque usually does not fluoresce early, and its intensity diminishes late. Finally, some eyes harbor a combination of plaques and hot spots. In these eyes, the hot spots may be at the edge of the plaque, may overlie the plaque, or may be far from the plaque.

High-speed or dynamic ICG angiography uses a scanning laser ophthalmoscope that takes up to 32 frames per second. These images are recorded like a movie, and the flow in and out of the vessels can actually be seen. The main use of dynamic ICG angiography is in the identification of CNV feeder vessels that are located in the Sattler layer of the choroid.


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