Indocyanine Green Angiography | Department of Ophthalmology

Indocyanine Green Angiography (ICG) is a valuable diagnostic method utilized to study blood flow in the choroid, which is the layer of blood vessels located beneath the retina.

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The procedure involves the injection of Indocyanine Green dye into a vein in your arm or hand. As the dye circulates through the blood vessels of the eye, images are captured to document the blood flow.

Due to a layer of pigmented cells obscuring the choroidal vessels, infrared light emitted by the ICG dye allows for imaging through this pigmented layer using specialized filters.

A primary application of indocyanine green angiography is to identify choroidal neovascularization, a frequent occurrence in age-related macular degeneration.

Recent insights into various inflammatory conditions have revealed distinct ICG patterns, enhancing our understanding of underlying disease processes.

What will you experience?

The procedure will typically last between 10 to 20 minutes, but you may spend 1 to 2 hours in our department overall.

Generally, Indocyanine Green dye is well tolerated. However, because the dye contains iodine, individuals with iodine allergies may experience serious reactions. Our medical staff will thoroughly review your medical history to confirm that you do not have allergies related to iodine, such as allergies to x-ray contrast mediums or shellfish. Additionally, ICG dye does not lead to discoloration of urine or skin.

Your pupils will be dilated to facilitate the ICG injection.

Post-dilation, your vision may be temporarily blurred. Therefore, we advise against driving after your pupils are dilated.

Before the procedure

EAT, DRINK & TAKE your medications as per your usual routine.

DRINK an additional 2-3 cups of water in advance of your appointment.

AVOID caffeine, including coffee, tea, or sodas.

BRING an English translator if needed.

BRING your lens case if you wear contact lenses, as you will need to remove them during the procedure.

Diagnostic procedure

Indocyanine green angiography (ICGA) serves as a diagnostic tool to evaluate choroidal blood flow and associated pathologies. Indocyanine green (ICG) is a water-soluble dye that fluoresces in the near-infrared spectrum (790-805 nm) with peak absorption in blood around 800-810 nm. This near-infrared light can penetrate ocular pigments like melanin and xanthophyll, making it invaluable for visualizing exudates and thin sub-retinal vascular layers. Age-related macular degeneration is among the leading causes of blindness globally, especially in developed nations. Hence, ICGA is essential for exploring choroidal neovascularization in patients with exudative age-related macular degeneration and for classifying drusen and subretinal deposits in non-exudative AMD.

Indications

The indications for indocyanine green angiography include:

Procedure

There are two primary techniques for indocyanine green angiography: fundus camera-based and scanning laser ophthalmoscope-based methods. The concentration of ICG dye varies depending on the instrument; typically, 25 ml of ICG dissolved in 5 ml of solvent is utilized, which can increase to 50 ml for patients with poorly dilated pupils or high pigmentation. For individuals with iodine allergies, a non-iodine dye like Infracyanine green should be used instead.

To perform the test, your pupils need to be dilated. The dye is injected as a bolus through the antecubital vein, followed by images being captured at various intervals until both retinal and choroidal circulations are maximally hyperfluorescent. Initial photos will be taken at approximately 30 to 60-second intervals, categorized into three phases:

1. Early phase at 60 seconds: Large choroidal arteries and veins are prominently visible.
2. Mid phase at 5-15 minutes: The choroidal vasculature becomes more diffuse, and hyperfluorescent lesions stand out against the dimming background.
3. Late phase at 15-30 minutes: Hyperfluorescent lesions are starkly contrasted against a dark backdrop, ideal for detecting choroidal neovascularization.

Advantages over fluorescein angiography

Indocyanine green angiography offers several advantages compared to standard fundus fluorescein angiography (FFA). Due to its protein-binding characteristics, there is less leakage from choriocapillaries, allowing for prolonged visibility in choroidal vessels. ICGA provides superior visualization of choroidal neovascularization, resulting in better patient tolerance than FFA.

History

The physical and physiological properties of indocyanine green dye were first detailed by Fox and Wood. Developed by Kodak Research Laboratories for cardiac output measurement, the first ICG angiogram in humans was achieved by Flower and Hochheimer, marking a pivotal point in the clinical application of this imaging technique. Subsequent advancements included infrared-sensitive video cameras and high-resolution digital imaging systems, improving the quality of ICG angiograms.

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