What is fluorescein angiography?
Fluorescein angiography is a diagnostic test that is used to study the circulation of the retina and, to a lesser extent, the layer beneath that nourishes it, the choroid. Although they are highly vascularised tissues, their networks of blood vessels cannot be seen with the naked eye.
Hence, it is necessary to carry out this test, which, despite the emergence of less invasive options, is still very useful due to its high sensitivity when assessing, quantifying and locating retinal lesions.
What does it consist of?
Fluorescein angiography consists of the intravenous injection of a contrast substance that travels through the blood until it reaches the blood vessels in the fundus and stain them. Thus, they can be viewed using sophisticated photographic equipment, which captures the images to form a complete map of the eye’s vascular network.
With wide-field systems it is possible, based on a single 200º photograph, to observe almost 90% of this circulatory network and reach even the most peripheral areas.
How is it performed?
This test requires dilating the pupil with drops (mydriatic eye drops), which take effect in about 15 minutes. From there, the contrast substance is injected and, once it appears in the vessels, after approximately 15 seconds, it takes about 5 to 15 more minutes to capture the images.
During the injection of the contrast substance, the patient may experience slight nausea, as well as a temporary feeling of warmth, but these are mild symptoms that disappear once the test is finished. On the other hand, the effects of pupil dilation (blurred vision and glare) are no longer felt after a few hours.
In what cases is it used?
As this is an invasive test for the patient and there are less uncomfortable alternatives, it is currently used less frequently for monitoring retinal pathologies. However, the information provided by this technique as a diagnostic tool is essential for early detection of lesions caused by diabetic retinopathy, vascular occlusions, uveitis or AMD, among other pathologies, hence being able to act in time and thus reducing the incidence of irreversible visual alterations.
Furthermore, there is another type of contrast test called indocyanine green angiography, in which the injection is performed with a different dye than the previous one. This allows for a more precise differentiation of the deeper vessels (of the choroid) and is, therefore, essential in pathologies such as uveitis or certain forms of wet AMD (polypoid variant).