Intravenous Fluorescein

Fluorescein

Fluorescein is a synthetic organic compound available as a dark orange/red powder soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications....

 angiography (IVFA) or fluorescent angiography is a technique for examining the circulation of the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

 using the dye tracing

Dye tracing

Dye tracing is tracking and tracing various flows using dye added to the liquid in question. The purpose of tracking may be an analysis of the flow itself, of the transport of something by the flow of the objects that convey the flow...

 method. It involves injection of sodium fluorescein

Fluorescein

Fluorescein is a synthetic organic compound available as a dark orange/red powder soluble in water and alcohol. It is widely used as a fluorescent tracer for many applications....

 into the systemic circulation, and then an angiogram

Angiogram

Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins and the heart chambers...

 is obtained by photographing the fluorescence

Fluorescence

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

 emitted after illumination of the retina with blue light at a wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 of 490 nanometers. The fluorescein dye also reappears in the patient urine, causing a yellow-green appearance. It can also cause discolouration of the saliva.

Fluorescein angiography is one of several health care

Health care

Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...

 applications of this dye, all of which have a risk of severe adverse effect

Adverse effect

In medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...

s. See fluorescein safety in health care applications.

Equipment

• Exciter filter: Allows only blue light to illuminate the retina. Depending on the specific filter, the excitation wavelength hitting the retina will be between 465-490 nm. Most only allow light through at a wavelength of 490 nm.
• Barrier filter: Allows only yellow-green light (from the fluorescence) to reach the camera. Both filters are interference bandpass filter
  Interference filter
  An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest...
  
  s, which means they block out all light except that at a specific wavelength. The barrier filter only allows light with a wavelength of 525 nm, but depending on the filter it can be anywhere from 520-530 nm.
• Fundus Camera
  Fundus camera
  A fundus camera or retinal camera is a specialized low power microscope with an attached camera designed to photograph the interior surface of the eye, including the retina, optic disc, macula, and posterior pole A fundus camera or retinal camera is a specialized low power microscope with an...
  
  , either digital or with camera body containing black and white, or slide positive film.

Technique

• Baseline 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 often gives a better image of the fundus than the color image.

• A 6 second bolus
  Bolus (medicine)
  In medicine, a bolus is the administration of a medication, drug or other compound that is given to raise its concentration in blood to an effective level...
  
   injection of 2-5cc 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 before and after the fluorescein reaches the retinal circulation (approximately 10 seconds after injection). The early images allow for the recognition of autofluorescence of the retinal tissues. 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
  Autofluorescence
  Autofluorescence is the natural emission of light by biological entities such as mitochondria and lysosomes, and is used to distinguish the light originating from artificially added fluorescent markers...
  
  . 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 — injection of fluorescein
• 9.5 sec — posterior ciliary arteries
• 10 sec — choroid
  Choroid
  The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye , while in the outlying areas it narrows to 0.1 mm...
  
  al flush (or "pre-arterial phase")
• 10-12 sec — retinal arterial stage
• 13 sec — capillary
  Capillary
  Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
  
   transition stage
• 14-15 sec — early venous stage (or "lamellar stage", "arterial-venous stage")
• 16-17 sec — venous stage
• 18-20 sec — late venous stage
• 5 minutes — late staining

Fluorescein enters the ocular circulation from the internal carotid artery

Internal carotid artery

In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....

 via the ophthalmic artery

Ophthalmic artery

The ophthalmic artery is the first branch of the internal carotid artery distal to the cavernous sinus. Branches of the OA supply all the structures in the orbit as well as some structures in the nose, face and meninges...

. 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 defects (i.e. capillary leakage, aneurysm

Aneurysm

An aneurysm or aneurism is a localized, blood-filled balloon-like bulge in the wall of a blood vessel. Aneurysms can commonly occur in arteries at the base of the brain and an aortic aneurysm occurs in the main artery carrying blood from the left ventricle of the heart...

, neovascularization

Neovascularization

Neovascularization is the formation of functional microvascular networks with red blood cell perfusion. Neovascularization differs from angiogenesis in that angiogenesis is mainly characterized by the protrusion and outgrowth of capillary buds and sprouts from pre-existing blood vessels.In...

)

pooling defects

staining

transmission (filling) defects

abnormal vasculature

Causes of hypofluorescence:

blocking defect (i.e. blood)

filling defect (capillary blockage)

Among the common groups of ophthalmologic disease, fluorescein angiography can detect diabetic retinopathy

Diabetic retinopathy

Diabetic retinopathy is retinopathy caused by complications of diabetes mellitus, which can eventually lead to blindness....

, vein occlusions, retinal artery occlusions, edema of the optic disc, and tumors.

Sources

• Richard, Gisbert „Fluorescein and ICG Angiography“, THIEME 1998, ISBN 0-86577-712-8
• Kanski, Jack „Clinical Ophthalmology“, 2006