61
Fluorescein Angiography
7
Fluorescein angiography (FA) was introduced in oph-
thalmology by Novotny and Alvis in the sixties of the last
century. They took serial fundus photographs after intra-
venous injection of sodium fluorescein to study the reti-
nal and choroidal circulation
(1)
. Initially, they used this
technique in diabetic and hypertensive patients and after,
the technique was used in age-related macular degenera-
tion (AMD). Although the clinical diagnosis of AMD
can be established based on patient’s history and fundus
examination, FA is the most important ancillary test for
classifying the disease in its different subtypes, especially
in its wet form. Nowadays, optical coherence tomogra-
phy (OCT) is being more used than FA for monitoring
the response to treatment, although FA is still very useful
in some cases.
Sodium fluorescein is a small molecule, with a molecular
weight of 376.27 daltons, and it is highly soluble in water.
It is stimulated by light in the range of 465-490 nm and
then it enters into a higher energy state. The molecule
emits longer wavelength fluorescence, between 520 and
530 nm, as it decays to a lower energy state. In clini-
cal application, two filters are used. An excitation filter
allows the passage of blue light, which stimulates the
fluorescein in the eye, which emits yellow-green light. In
addition, a barrier filter is used to block some reflected
blue light, allowing only the yellow-green light to pass
through. This resultant fluorescence is recorded by a
camera as an image
(2)
.
Sodium fluorescein diffuses through the fenestrated ves-
sels of the choriocapillaris, but does not cross the internal
and the external blood-retinal barriers. Thus, any con-
dition that compromises these barriers, obstructs blood
flow, or changes the normal pigmentation of the retinal
pigment epithelium (RPE) can cause abnormalities on
FA.
The dye is removed from the vascular compartment by
the kidney. It is relatively inert, making intravenous injec-
tion safe and severe adverse reactions rare. Nevertheless,
the patient should be properly informed of the potential
risks of FA injection
(3)
.
2. Interpretation
Several FA patterns can be observed in AMD patients.
They can be classified at those leading to decreased fluo-
rescence (hypofluorescence) or increased fluorescence
(hyperfluorescence). Hypofluorescence either represents
blocked fluorescence or a vascular filling defect (Table 1).
Hyperfluorescence can be the result of loss of the normal
barrier to background choroidal fluorescence known as
transmitted fluorescence. A second reason for hyperfluo-
rescence can arise from extravascular accumulation of the
dye or from leakage from abnormal vessels (Table 2)
(4)
.
By convention, leakage of fluorescein into a space is
referred to as pooling, while leakage into a tissue is called
staining
(5)
.
1. Introduction
Authors:
Luis Arias, MD
1 2
Jordi Monés, MD
2
1
Hospital Universitari de Bellvitge - University of Barcelona. Spain
2
Institut de la Màcula i de la Retina - Centro Médico Teknon - Barcelona. Spain
