Indocyanine Green Angiography | Department of Ophthalmology

Indocyanine Green Angiography (ICG) is a diagnostic procedure that uses ICG dye to examine the blood flow in the CHOROID &#; the layer of blood vessels which lies underneath the retina.

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Indocyanine Green dye is injected into a vein in the arm/hand. As the dye passes through the blood vessels of your eye, photographs are taken to record the blood flow.

The choroidal vessels are hidden beneath a layer of pigmented cells. Infrared light given off by ICG dye can be imaged through the pigmented layer using special filters.

The most common application of indocyanine green angiography is the detection of choroidal neovascularization, a common component of age related macular degeneration.

In multiple inflammatory conditions, as well as with central serous chorioretinopathy, distinct ICG patterns have emerged that may facilitate better understanding of the disease processes.

What will you experience?

The actual procedure will take 10-20 minutes. The average length of stay in our department can be 1-2 hours.

The Indocyanine Green dye is generally tolerated without any problems. However, ICG dye contains iodine. Severe allergic reactions are possible in people who are allergic to iodine. Our nurse will review your medical history to ensure you are not allergic to substances that contain iodine, such as x-ray dyes and shellfish. ICG dye does not cause urine or skin discoloration.

Your pupils will be dilated for the ICG.

After the pupils are dilated your vision may become blurred. Driving is not recommended when your pupils are dilated.

Before the procedure

EAT, DRINK & TAKE your medications as you usually do.

DRINK an extra 2-3 cups of water before the procedure.

AVOID coffee, tea, or caffeinated beverages.

BRING an English translator.

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

Diagnostic procedure

Choroidal blood flow revealed with indocyanine green angiography

Indocyanine green angiography (ICGA) is a diagnostic procedure used to examine choroidal blood flow and associated pathology. Indocyanine green (ICG) is a water soluble cyanine dye which shows fluorescence in near-infrared (790&#;805 nm) range, with peak spectral absorption of 800-810 nm in blood.[1][2] The near infrared light used in ICGA penetrates ocular pigments such as melanin and xanthophyll, as well as exudates and thin layers of sub-retinal vessels.[3] Age-related macular degeneration is the third main cause of blindness worldwide, and it is the leading cause of blindness in industrialized countries.[4] Indocyanine green angiography is widely used to study choroidal neovascularization in patients with exudative age-related macular degeneration.[5] In nonexudative AMD, ICGA is used in classification of drusen and associated subretinal deposits.[5]

Indications

Indications for indocyanine green angiography include:

Procedure

Fundus camera-based indocyanine green angiography techniques and scanning laser ophthalmoscope-based indocyanine green angiography techniques are there.[10] The concentration of indocyanine green dye may vary according to instrument used. For fundus cameras, 25 ml ICG dissolved in 5 ml solvent is used, it may be increased to 50 ml in patients with poorly dilated pupil and high pigmentation.[6] In case of iodine allergy, instead of ICG, iodine-free dye Infracyanine green should be used.[11]

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To perform test, pupil should be dilated. The dye is injected through the antecubital vein as bolus.[12] Images are taken in several second intervals until the retinal and choroidal circulations are maximally hyperfluorescent.[10] Then for first few minutes, take photos at approximately 30 to 60 second intervals. Pictures taken are classified under three phases:[13]

1. Early phase at 60 seconds: large choroidal arteries and veins are highlighted in this phase.

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2. Mid phase at 5&#;15 minutes: in this phase choroidal vasculature become less distinct and more diffuse, and hyperfluorescent lesions appear bright against the fading background.

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3. Late phase at 15&#;30 minutes: in this phase hyperfluorescent lesions appear bright against the dark background.

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   The choroidal neovascularization are best detected in this phase.

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Advantages over fluorescein angiography

Indocyanine green angiography has many advantages over commonly used fundus fluorescein angiography (FFA). Because of its protein-binding properties, its leakage from choriocapillaries is less and thus it will remain longer in choroidal vessels compared to fluorescein dye.[1] Choroidal neovascularization is better visualized by ICGA, than fluorescein angiography.[5] The patient toleration is also better compared to FFA.[12]

History

Physical and physiological properties of indocyanine green dye were first described by Fox and Wood, in .[15] Indocyanine green angiography was developed by Kodak Research Laboratories for determining cardiac output. In , Kogure et al. performed intra-arterial choroidal absorption angiography using indocyanine green dye in monkeys.[16] In the year , using ICGA, Kogure and Choromokos studied cerebral circulation in a dog. In , Hochhimer replaced color film with black and white infrared film. First human ICG angiogram was of carotid artery. First intravenous ICGA in human eye was performed by Flower and Hochheimer in .[12][6] In Hayashi et al. used infrared-sensitive video camera to perform ICGA.[10] In the year , Guyer et al. introduced the use of high resolution ( × ) digital imaging system coupled with infrared video cameras to produce better high resolution images.[17]

See also

References