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. 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. Age-related macular degeneration is the third main cause of blindness worldwide, and it is the leading cause of blindness in industrialized countries. Indocyanine green angiography  is widely used to study choroidal neovascularization in patients with exudative age-related macular degeneration. In nonexudative AMD, ICGA is used in classification of drusen and associated subretinal deposits. 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. 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. In case of iodine  allergy, instead of ICG, iodine-free dye Infracyanine green should be used. To perform test, pupil should be dilated. The dye is injected through the antecubital vein as bolus. Images are taken in several second intervals until the retinal and choroidal circulations are maximally hyperfluorescent. Then for first few minutes, take photos at approximately 30 to 60 second intervals. Pictures taken are classified under three phases: Advantages over fluorescein angiography. Indocyanine green angiography has many advantages over commonly used fundus fluorescein angiography (FFA). Because of its protein-bounding properties, its leakage from choriocapillaries is less and thus it will remain  longer in choroidal vessels compared to flourescein dye. Choroidal neovascularization is better visualized by ICGA, than fluorescein angiography. The patient toleration is also better compared to FFA. History. Physical and physiological properties of indocyanine green dye were first described by Fox and Wood, in 1960. Indocyanine green angiography was developed by Kodak Research Laboratories for determining cardiac output. In 1968, Kogure et al. performed intra-arterial choroidal absorption angiography using indocyanine green dye in monkeys. In the year 1969, using ICGA, Kogure and Choromokos studied cerebral circulation in a dog. In 1971, 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 1972. In 1986 Hayashi et al. used infrared-sensitive video camera to perform ICGA. In the year 1992, Guyer et al. introduced the use of high resolution (1024 × 1024) digital imaging system coupled with infrared video cameras to produce better high resolution images.