ICG Angiography

Window to the Choroid

Indocyanine green angiography (ICGA) enables imaging of the choroidal circulation below the retinal pigment epithelium (RPE). ICGA complements fluorescein angiography (FA), which captures blood flow above the RPE. Although ICG angiography is not a replacement for fluorescein, it provides adjunctive information which assists in defining the choroidal circulatory involvement in retinal pathology.

Early attempts at ICGA met with little success because image quality was poor and yielded little important clinical information. SPECTRALIS^® cSLO imaging has sparked renewed interest in ICGA. Instead of the cloudy, still images traditionally associated with ICGA, the SPECTRALIS confocal technology avoids the scattered light from flash photography and produces video images of stunning clarity.

The light used for ICGA penetrates deeper into tissue and is not absorbed by the RPE the way fluorescein illumination is. ICGA provides a different and deeper picture of the retina than FA.

ICGA provides useful information about a variety of significant conditions including CNV, RAP, CSCR, and Serous PED.

One of the strongest applications of ICGA is with choroidal neovascularization (CNV). ICGA offers a clearer picture, helping clinicians differentiate between occult and classic CNV. ICGA’s unique properties mean that areas of CNV beneath blood, exudate, or pigment epithelial detachment can be imaged more readily. ^{Yannuzzi 1992}

A form of neovascular age-related macular degeneration known as retinal angiomatous proliferation (RAP) is believed by some to indicate a more aggressive form of CNV. While FA imaging is not always able to identify RAP, ICGA lights up choroidal circulation to the RAP lesion, providing a stronger chance of identification. As a result of more widespread use of ICGA, estimates of the frequency of RAP have been increasing and now range from 10% to 28% of all CNV cases.

ICGA may also provide useful information about central serous chorioretinopathy (CSCR). FA does not provide evidence as to whether the initial abnormality is at the level of the RPE or the choroid; ICGA enables assessment of the underlying choroidal hyperpermeability.

Another application of SPECTRALIS dynamic ICGA is the management of Serous PED. Just like with its video FA, SPECTRALIS ICGA documents dye movement with high speed (16 frames per second) movies. In Serous PED, the first 15-20 seconds of the video can be crucial, because it shows feeder and draining vessels. Some doctors use high-speed ICGA to direct therapies, such as PDT, directly to feeder vessels.

Visit the image gallery to see more ICGA videos.