Fluorescein Angiography

Fluorescein angiography (FA), fluorescent angiography (FAG), or fundus fluorescein angiography (FFA) is a technique for testing the circulation of the retina and choroid (parts of the fundus) using a fluorescent color and a specialized angiographic camera. It involves administration of salt fluorescein into the systemic blood circulation, and then an angiogram is acquired by photographing the fluorescence produced after lighting of the retina with blue light at a wavelength of 490 nanometers.

What Is Fluorescein Angiography?

The test uses the color tracing approach. The fluorescein is administered intravenously in intravenous fluorescein angiography (IVFA) and orally in oral fluorescein angiography (OFA).

The fluorescein dye also reappears in the patient urine, triggering the urine to appear darker, and sometimes orange. It can likewise cause discolouration of the saliva.

fluorescein angiography
Photo By L. Bacud – Own work, CC BY-SA 3.0, wikimedia.org

Fluorescein angiography is among a number of healthcare applications of this color, all of which have a risk of severe negative impacts. See fluorescein safety in healthcare applications. Fluorescein angiography does not include making use of ionizing radiation.

Equipment for Fluorescein Angiography Procedure

  • Exciter filter: Allows just blue light to illuminate the retina. Depending on the particular filter, the excitation wavelength hitting the retina will be between 465-490 nm. Many just enable light through at a wavelength of 490 nm.
  • Barrier filter: Allows just yellow-green light (from the fluorescence) to reach the video camera. Both filters are interference bandpass filters, which implies they block out all light except that at a specific wavelength. The barrier filter only allows light with a wavelength of 525 nm, however depending on the filter it can be anywhere from 520-530 nm.
  • Fundus Camera, either digital or with cam body containing black and white, or slide positive film.

How Is Fluorescein Angiography Performed?

  • Standard color and black and white red-free filtered images are taken prior to injection. The black and white images are filtered red-free (a green filter) to increase contrast and typically offers a better picture of the fundus than the color image.
  • A 6-second bolus injection of 2-5cc of salt fluorescein into a vein in the arm or hand.
  • A series of black-and-white or digital photographs are taken of the retina prior to and after the fluorescein reaches the retinal circulation (around 10 seconds after injection). The early images permit the acknowledgment of autofluorescence of the retinal tissues. Photos are taken roughly once every second for about 20 seconds, then less often. A postponed image is obtained at 5 and 10 minutes. Some physicians like to see a 15-minute image too.
  • A filter is placed in the cam so just the fluorescent, yellow-green light (530 nm) is taped. The cam might however pick up signals from pseudofluorescence or autofluorescence. In pseudofluorescence, non-fluorescent light is imaged. This occurs when blue light reflected from the retina passes through the filter. This is usually a problem with older filters, and annual replacement of these filters is suggested. In autofluorescence, fluorescence from the eye occurs without injection of the color. This might be seen with optic nerve head drusen, astrocytic hamartoma, or calcific scarring.
  • Black-and-white photos provide much better contrast than color images, which aren’t essential because just one color is being transmitted though the filter.

Normal circulatory filling

Times are approximate:

0 seconds – injection of fluorescein
9.5 sec – posterior ciliary arteries
10 sec – choroidal flush (or “pre-arterial phase”).
10 – 12 sec – retinal arterial stage.
13 sec – capillary transition stage.
14 – 15 sec – early venous stage (or “laminar stage”, “arterial-venous stage”).
16 – 17 sec – venous stage.
18 – 20 sec – late venous stage.
5 minutes – late staining.

Fluorescein gets in the ocular flow from the internal carotid artery by means of the ophthalmic artery. The ophthalmic artery provides the choroid by means of the brief posterior ciliary arteries and the retina through the main retinal artery, however, the path to the choroid is typically less circuitous than the route to the retina. This represents the short delay in between the “choroidal flush” and retinal filling.

Pathologic findings

Pathologic changes are acknowledged by the detection of either hyperfluorescence or hypofluorescence.

Causes of hyperfluorescence:

  • window/transmission (filling) defects.
  • leaking flaws (i.e. capillary leak, aneurysm, neovascularization).
  • pooling problems.
  • staining.
  • unusual vasculature.

Causes of hypofluorescence:

  • blocking defect (i.e. blood).
  • filling defect (capillary nonperfusion/blockage).

Fluorescein angiography is used by doctors concentrating on the treatment of eye diseases (eye doctors) to evaluate the vasculature of the retina, choroid, optic disc, and iris. Amongst the common groups of ophthalmologic disease, fluorescein angiography can identify diabetic retinopathy (neovascularization), vein occlusions, retinal artery occlusions, edema of the optic disc, and growths. Additionally, the transit time (the duration between injection of the color when it appears in the taken a look at capillary) can provide an unbiased measurement of the rate of blood circulation through the imaged blood vessels.

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