Fluorescein angiography

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.

Some patients have an allergic reaction to the dye. The most common reaction is nausea that is typically transient. The nausea usually subsides very quickly. It comes on due to a difference in the pH from the body and the pH of the sodium fluorescein dye. Other reactions due happen however are much less common. Such as, hives which can range from a minor annoyance to severe and would require an antihistamine to resolve. Rarely does one experience anaphylactic shock from an injection of sodium fluorescein dye. However, it can happen so make sure your health care provider has a crash cart in case of emergency.

Equipment

 * 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 1990s.

Technique

 * 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.

Normal circulatory filling
times are approximate
 * 0 seconds &mdash; injection of fluorescein
 * 9.5 sec &mdash; posterior ciliary arteries
 * 10 sec &mdash; choroidal flush (or "pre-arterial phase")
 * 10-12 sec &mdash; retinal arterial stage
 * 13 sec &mdash; capillary transition stage
 * 14-15 sec &mdash; early venous stage (or "lamellar stage", "arterial-venous stage")
 * 16-17 sec &mdash; venous stage
 * 18-20 sec &mdash; late venous stage
 * 5 minutes &mdash; late staining

Fluorescein enters the ocular circulation from the internal carotid artery via the ophthalmic artery. The ophthalmic artery supplies the choroid via the short posterior ciliary arteries and the retina via the central retinal artery, however, the route to the choroid is typically less circuitous than the route to the retina. This accounts for the short delay between the "choroidal flush" and retinal filling.

Pathologic findings
Pathologic changes are recognized by the detection of either hyperfluorescence or hypofluroescence.

Causes of hyperfluorescence:
 * leaking (i.e. capillary leakage, aneurysm, neovascularization)
 * pooling (serous retinal detachment)
 * staining
 * transmission defects
 * abnormal vessels

Causes of hypofluorescence:
 * optical barrier (i.e. blood)
 * filling defect (capillary blockage)

Among the common groups of ophthalmologic disease, fluorescein angiography can detect diabetic retinopathy, vein occlusions, retinal artery occlusions, edema of the optic disc, and tumors.

Other types of fluorescent angiography

 * Indocyanine Green Angiography