Fluorescein angiography, or fluorescent angiography, is a technique for examining the circulation of the retina using the dye tracing method. It involves injection of sodium fluorescein into the systemic circulation, and then an angiogram is obtained by photographing the fluorescence emitted after illumination of the retina with blue light at a wavelength of 490 nanometers. The fluorescein dye also reappears 12-24 hours in the patient urine, causing a yellow-green appearance.
- Exciter filter: allows only blue light to illuminate the retina. It reduces the amount of non-fluorescent light that can reach the film, and allows for maximum excitation of the fluorescein.
- Barrier filter: allows only yellow-green light (from the fluorescence) to reach the camera. It absorbs the blue light used to illuminate the retina.
- Camera with black and white film. Also digital cameras have come into use since the late 1990’s.
- Baseline color and red-free filtered images are taken prior to injection. This allows for the recognition of autofluorescence of the retinal tissues.
- A 6 second bolus Injection of approximately 5cc of sodium fluorescein into a vein in the arm or hand.
- A series of black-and-white or digital photographs are taken of the retina after the fluorescein reaches the retinal circulation (approximately 10 seconds after injection). Photos are taken approximately once every second for about 20 seconds, then less often. A delayed image is obtained at 5 and 10 minutes. Some doctors like to see a 15 minute image as well.
- A filter is placed in the camera so only the fluorescent, yellow-green light (530 nm) is recorded. The camera may 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 generally a problem with older filters, and annual replacement of these filters is recommended. In autofluorescence, fluorescence from the eye occurs without injection of the dye. This may be seen with optic nerve head drusen, astrocytic hamartoma, or calcific scarring.
- Black-and-white photos give better contrast than color photos, which aren’t necessary since only one color is being transmitted though the filter.