Indications (Why you are having the test)
You have a disorder in the back of the eye, which involves the retina or the area behind it. The retina is the light receptive membrane at the back of the eye, which collects the visual image and transmits it to the brain via the visual pathways.
Many disorders of the retina can be seen by looking directly into the eye. Some examples of this include: retinal detachment, bleeding, masses, pigment changes. There is a lot, however, that cannot be seen such as leaky vessels and changes in the pigment layer between the retina and the choroid. This is where fluorescein angiography is useful.
With fluorescein angiography a fluorescent dye (fluorescein) is injected into a vein; this passes through the circulation and reaches the retinal and choroidal blood vessels, which are situated on either side of the retina and are separated by an impenetrable and relatively visually opaque layer called the retinal pigment epithelium. Blue light is shone over the retina and the fluorescein turns green.
Images taken with a camera will only show us the dye and where it has gone over time. Multiple pictures over several minutes are taken forming a mini-movie of the dye passing through the blood vessels and elsewhere if there is something wrong.
What is involved?
A small cannula is inserted into a vein, usually in the forearm, and the dye is injected. Moments after injection, photos are taken with a camera that is looking into the back of the eye.
A suitable vein is located, the dye is injected, and a series of photographs are taken with the fundus camera
What are the side effects?
- Yellow appearance for a few hours after the injection
- Dark yellow urine
- Nausea (5%)
- Itching
- Rash
- Fainting
- Anaphylactic shock – Very rare but potentially serious, requiring resuscitation.
What does the test show the doctor?
Normally in the healthy eye, all of the fluorescein remains in the retinal blood vessels; travelling first through the choroid and then the retinal vessels, followed by excretion in the urine.
The dye has passed through the choroid and remains in the retinal vessels. Note that there is no leakage.
In some conditions there is a breakdown of the opaque retinal pigment epithelial barrier separating the circulation in front of and behind the retina. If this layer is deficient the choroidal circulation is unmasked; an example of this being Age Related Macular Disease.
In this case of dry AMD, the areas of pigment atrophy (loss) lead to unmasking of the choroidal vessels and the sclera (white eye coat) beneath.
Sometimes there is leakage from the blood vessels themselves, again with leakage into the retinal tissue; an example of this is Diabetes or Vein occlusion where the vessels become leaky.
Here you can see two features – the dots lighting up are dilatations in the retinal vessels called aneurysms. There is patchy diffuse leakage around these as they tend to leak, leading to swelling of the retina and loss of vision.
In the case of Retinal Artery Occlusion there is no blood and therefore no dye passing through the vessel at all.
Here there is a blockage of the superior (upper) retinal branch artery. The striking thing is that there is no blood passing through it in all phases of the angiogram when compared with the vessels below.
If there is a breakdown of the normal barrier between the retinal and choroidal circulations (retinal pigment epithelium), there will be pooling of dye underneath the retina; an example of this is Central Serous Retinopathy.
Here there is a defect in the retinal epithelial pigment layer leading to fluid leakage which appears as the classical smokestack.
Conditions where there are new vessels forming are very well demonstrated with angiography because the new vessels leak profusely. Examples of this are Diabetes, Age Related Macular Disease and Vein Occlusions.
The macula lights up here since there is a neovascular (new vessel) membrane beneath it that leaks profusely. This is an example of early wet AMD.
If there is a haemorrhage into or beneath the retina, there will be no fluorescein seen on the angiogram because it is blocked from view.
The haemorrhage has blocked the fluorescein from view. This is a case of late wet AMD.
Finally, sometimes material which has formed in the retina or deeper to it stains with fluorescein.
Late angiogram pictures show these drusen deposits (found in dry AMD) which stain with fluorescein.
Fluorescein angiography is a useful investigative tool when trying to identify reasons for poor vision following cataract surgery.
In this case the patient had poor vision despite uncomplicated cataract surgery. The leakage of fluid at the macula is typical of Cystoid Macular Oedema (CMO). See under cataract surgery complications.
Summary
Fluorescein angiography is an excellent examination tool which graphically illustrates pathological processes. Furthermore it is useful in monitoring a condition or therapeutic response to a treatment.
