What is FFA eye test and what is FFA full form?
The full form of the FFA eye test is Fundus Fluorescein angiography. It is one of the fundamental imaging techniques of the eye, mainly the retina. It helps in the diagnosis and differentiation of retinal diseases. The FFA eye test determines the need for laser treatment of the retina. Angiography of the heart looks in detail at the blood vessels of the heart. Similarly, an FFA eye test is nothing but an angiography for the retinal blood vessels using the Fluorescein dye. It gives us minute details about the blood supply of the retina.
How is this angiography for the eyes performed?
This angiogram for the eyes takes about 20 to 30 minutes.
- The pupils are dilated.
- Anethestist makes sure patient is comfortable.
- Anesthetist inserts a vienflow (IV Line)in one vein of the patients forearm and secures it
- Your ophthalmologist prepares the fundus camera and makes sure all patient details are entered in the sytem
- A black and white fundus photograph or photo of the retina and optic nerve is taken.
- A colour photograph of the retina and optic nerve is also taken
- Anethestist then gives a 6-second bolus injection of 2-5 cc of sodium fluorescein into a vein in the arm through the veinflow. In the earlier days the dye used to be given orally. This was also known as oral fluorescein angiography. These days inly the intravenous injection route is used.
- 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).
- These early images are important because they 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.
How does the FFA camera work
The ffa equipment is a camera which can take pictures of the retina.
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. 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 thus done. 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 because the filter transmits only one color of light.
The dye flows through the retinal vessels and this is what the fundus photographs pick up. If there is any leakage of fluorescein from these blood vessels that will be clearly seen in the photographs.
What are the phases of an FFA test for eye ?
These timings are approximate
- 0 seconds – injection of fluorescein
- 9.5 sec – posterior ciliary arteries
- 10 sec – choroidal flush or choroidal fluorescence (or "pre-arterial phase") - this is when the dye is entering the choroidal circulation. The choroid is an extremely vascular tissue and as the choroidal vessels fill up with the dye there is generalized flurescence that is seen in the fundus photograph. The entire picture appears to light up. This however is not a detailed view of the choroid and this lack of detail is because of a layer in front of the choroid called the retinal pigment epithelium.
- 10–12 sec – retinal arterial stage
- 13 sec – capillary transition stage or arteriovenous phase
- 14–15 sec – early venous stage (or "laminar stage", "arterial-venous stage")
- 16–17 sec – venous phase
- 18–20 sec – late venous stage
- After 4-5 minutes after injection begins the recirculation phase and the late phase
- 5 minutes – late staining or late phase.
The retinal vessles are empty of the fluorescein by 10 minutes after the injection. The optic nerve head appears fluorescent in the late phases due to staining
Which parts of the eye does the FFA eye test check ?
The FFA is an angiography and is able to take pictures of all areas of the eye which can be photographed and have blood vessels
- Optic Nerve
The choroid and Iris are supplied by ciliary artieries whch are branches of the ophthalmic artery.
Apart from these parts of the eye what else does an FFA test for eye tell us ?
We mentioned earlier that the dye takes approximately 10-12 seconds to reach the eye. If however, the time is increased then that indicates impaired blood flow to the eye. In other words even though the patient is having vision problems the primary problem may be something else. To rule out blockage of the common carotid and internal carotid artery a doppler sonography may be advised.
In which conditions is this angiography for eyes / FFA test done?
Here is a list of a few conditions where this angiography for eyes is advised.
- Diabetic Retinopathy - Diabetic macular edema will show pooling of the dye
- Choroidal neovascular membrane ( CNVM)
- Central retinal vein occlusion
- Central retinal artery occlusion - This can occur because of a vascular event or also a
- Neuroophthalmic condition like Giant cell arteritis
- Polypoidal choroidal vasculopathy
Following are some eye conditions where FFA is not done routinely these days
- ARMD - Age related macular degeneration - OCT or Optical Coherence Tomography has become the primary investigation for this condition
- Retinal detachment
Terms used to describe the behavior of dye in the photographs
- Blocked fluorescence
This is when the flourescence is blocked. Depending on which ciculation is not visible one can ascertain which part of the eye is affected.
- If the problem is preretinal or in front of the retina then the retinal and choroidal vasculature will be blocked. Like in vitreous hemorrhage, cataract, preretinal hemorrhage.
- If the problem is in the retina then the capillary circulation in the retina is not seen but the larger vessels in the retina are seen. Like in dot and blot hemorrhages of the retina or intraretinal lipid that occurs in diabetic retinopathy.
- If the problem is prechoroidal or in front of the choroid then the choroidal circulation is not seen while retinal circulation is seen. Like in retinal pigment epithelium hypertrophy, subretinal hemorrhage
- Hypo - fluorescence - This means that the blood flow to the retina is compromised. This happens in conditions like diabetic retinopahthy, retinal vein occlusions, inflammation of the retinal blood vessels ( Vasculitis).
- Hyper - Fluorescence - Capillary hyper fluorescence is mainly divided into 1) Autofluorescence 2) Transmission defect (window defect) 3) Leaking 4) Pooling and 5) Staining.
- Filling defect
- Pooling of dye - by looking at the retinal vessels one may even say Sub-retinal pooling. The dye gets collected inthe potential spaces of the retina viz. sub retianal space ( like in CSR) or sub RPE space ( Like in PED). This may also happen in certain malformations of blood vessels in the retina or choroid like capillary hemangiomas etc.
- Transmission defect (window defect): A window defect refers to the choroidal fluorescence produced by a relative decrease or absence of pigment in the RPE or an absence of Retinal pigment epithelim.
- Laminar flow occurs in the early venous phase followed by more homogenous vein filling in the later venous stage. Laminar meaning initially the dye only flows along the vessel walls and the center of the vessel does not contain dye.
- Optic disc leakage - this is also described as excess fluorescence and is seen in conditions like Anterior Ischaemic Optic Neuropathy or AION. Giant cell arteritis usually causes arteritic AION and should be treated urgently. Also seen in Lebers hereditary.
What are the possible adverse effects of FFA eye test?
- A person may feel a wave of nausea (feel sick) for 30 to 60 seconds after the injection. This is especially true if you have had a heavy meal before the test. For this reason, it is a good idea not to have a heavy meal before your appointment.
- A strange taste at the back of your mouth after the injection
- The injection site can be painful if the dye leaks from the vein into the surrounding tissue.
- A mild headache.
- An allergic reaction. Please let the doctor know if you have allergies or have had a severe allergic reaction before performing FFA eye test
- Your urine would be yellow for that day as the body throws out the dye.
When can fundus fluorescein angiography not be done
Usually we cannot perforom the FFA test for eye because of dye related issues
- If the patient has chronic kidney disease then the dye can cause renal toxicity
- If the patient is allergic to the dye.
- Angiography during pregnancy is also avoided