Fundus flourescein angiography (FFA) is a valuable
tool in the diagnosis and management of a large number of fundus disorders.
Basically, FFA gives information by allowing the examiner to study the changes, produced by various fundus disorders, in the flow of fluorescein dye along the vasculature of the retina and choroid. Indications. It is indicated in many disorders of ocular fundus, viz., (1) Diabetic retinopathy (2) Vascu-lar occlusions; (3) Eales’ disease. (4) Central serous retinopathy, (5) Cystoid macular oedema.
Technique.
The technique of FFA comprises of rapidly injecting 5 ml of 10 per cent solution of sterile sodium fluorescein dye in the antecubital vein and taking serial photographs (with fundus camera) of the fundus of the patient who is seated with pupils fully dilated. The fundus camera has a mechanism to use blue light (420-490 nm wavelength) for exciting the fluorescein present in blood vessels and to use yellow-green filter for receiving the fluorescent light (510-530 nm wavelength) back for photography.
The first photograph is taken after 5 seconds, then every second for next 20 seconds and every 3-5 seconds for next one minute. The last pictures are taken after 10 minutes.
Complications. FFA is comparatively a safe procedure. Minor side effects include : discoloration of skin and urine, mild nausea and rarely vomiting. Anaphylaxis or cardiorespiratory problems are extremly rare. However, a syringe filled with dexamethasone and antihistaminic drug along with other measures should be kept ready to deal with such catastrophy.
Phase of angiogram. Normal angiogram consists of following overlapping phases:
1. Pre-arterial phase. Since the dye reaches the choroidal circulation 1 second earlier than the retinal arteries, therefore in this stage choroidal circulation is filling, without any dye in retinal arteries.
2. Arterial phase. It starts 1 second after prearterial phase and lasts until the retinal arterioles are completely filled.
involves the complete filling of retinal arterioles and capillaries with a laminar flow along the retinal veins
4. Venous phase. In this phase veins are filling and arterioles are emptying. This phase can be subdivided into early, mid, and late venous phase.
Abnormalities detected by FFA. In the blood fluorescein is readily bound to the albumin. Normally the dye remains confined to the intravascular space due to the barriers formed by the tight junctions between the endothelial cells of retinal capillaries (in-ler blood-retinal barrier) and that between the pig-nent epithelial cells (outer blood retinal barrier).
In diseased states abnormalities in the form of lyperfluorescence and hypofluorescence may be letected on FFA. !. Hyperfluorescence. The causes are :
a) A window defect in RPE due to atrophy shows background choroidal fluorescence.
b) Pooling of dye under detached RPE.
c) Pooling of dye under sensory retina after breakdown of the outer blood-retinal barrier as
occurs in central serous retinopathy (CSR).
i) Leakage of dye into the neurosensory retina due to a breakdown in inner blood-retinal barrier e.g. as seen in cystoid macular edema (CME).
e) Leakage of dye from the choroidal or retinal neovascularization e.g. as seen in cases of proliferative diabetic retinopathy, and subretinal neovascular membrane in age-related macular degeneration.
(f) Staining i.e. long retention of dye by some tissues e.g. as seen in the presence of drusen.
(g) Leakage of dye from optic nerve head as seen in papilledema.
2. Hypofluorescence. The causes are:
(a) Blockage of background fluorescence due to abnormal deposits on retina e.g. as seen due to the presence of retinal haemorrhage, hard exudates and pigmented clumps.
(b) Occlusion of retinal or choroidal vasculature, e.g. as seen in central retinal artery occlusion and occlusion of capillaries in diabetic retinopathy.
(c) Loss of vasculature as occurs in patients with choroideremia and myopic degeneration.
