Indocyanine green angiography

Diagnostic procedure

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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

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Indications for indocyanine green angiography include:

Procedure

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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]

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.[14]
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.[14]
3. Late phase at 15&#;30 minutes: in this phase hyperfluorescent lesions appear bright against the dark background.[14] The choroidal neovascularization are best detected in this phase.[14]

Advantages over fluorescein angiography

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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

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Want more information on Indocyanine Green Angiography? Feel free to contact us.

Additional resources:
Functionality and Comfort Design of Lower-Limb Prosthetics
Capturing Eye Health: Laser Retinal Photography

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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

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References

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Frequently asked questions

How long does the test last?

The test lasts for about 10 minutes in the case of the fluoresceinography and, in the case of the indocyanography around 40 minutes. Nevertheless, the total time that the patient spends in the centre from arrival to departure is around 1 hour.

Should the test be done on an empty stomach?

You do not need to fast before the test. You should have breakfast like any other day but not eat excessively.

Should I come accompanied?

It is very important to come to the test with someone else, because your vision will be temporarily blurred. Your pupil will be dilated so you will not be able to drive after the test.

Are there any side effects?

The side effects that pupils may experience from the test are the result of pupils being dilated and may include glare and blurred vision. During the test we can see the flashes and lights that are emitted by the apparatus and on occasions we may experience some nausea or temporary heat. In some exceptional occasions stronger sensations may be experienced.

After the test the patient may continue to experience blurred vision for a few hours as a result of the dilating drops. Some patients may also experience a change in skin colour or the colour of their urine, as the dye is eliminated through the urine.

What happens if I have an unexpected reaction to the dye?

We have a medical and nursing team who are trained in resuscitation and are available at all times in case of an emergency.

How long do the side effects last after the test?

The glare effects last for as long as the effects of the eye drops, which can last for around 4 hours, while the change in urine colour can last for 1 to 3 days, depending on the patient&#;s renal function.

What are the advantages of having the angiography at the ICR?

ICR has the best technology on the market. The highly versatile tool that we use can be adapted and focused depending on the patient&#;s illness to obtain detailed images of the internal layers of the eye, as well as combining the angiography with another test that provides lots of information, the optical coherence tomography (OCT).

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