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The fluorescein is administered intravenously in intravenous fluorescein angiography (IVFA) and orally in oral fluorescein angiography (OFA). The test is a dye tracing method. The fluorescein dye also reappears in the patient urine, causing the urine to appear darker, and sometimes orange. [2] It can also cause discolouration of the saliva.
From a physics perspective, both dye-based methods utilize the phenomenon of fluorescence. For FA, this corresponds to an excitation wavelength of blue (around 470 nm) and an emission wavelength near yellow (520 nm). [49] For IGCA, the newer method, the excitation wavelength is between 750 and 800 nm while emission occurs above 800 nm. [50]
Digital subtraction angiography (DSA) is a fluoroscopy technique used in interventional radiology to clearly visualize blood vessels in a bony or dense soft tissue environment. Images are produced using contrast medium by subtracting a "pre-contrast image" or mask from subsequent images, once the contrast medium has been introduced into a ...
Optical coherence tomography (OCT) is a technology using near-infrared light to image the eye, in particular penetrate the retina to view the micro-structure behind the retinal surface. Ocular OCT angiography (OCTA) is a method leveraging OCT technology to assess the vascular health of the retina. [15]
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Fluorescein is a dye which is taken up by damaged cornea such that the area appears green under cobalt blue light. [3] There is also a version that comes premixed with lidocaine. [4] [8] Fluorescein was first made in 1871. [9] It is on the World Health Organization's List of Essential Medicines. [10]
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]
Angiography is a process of photographing/recording vascular flow within the retina and surrounding tissue by injecting a fluorescent dye into the blood stream. This dye fluoresces a different colour when light from a specific wavelength (excitation colour) reaches it.