FFA anf ICG aniography Flashcards
What is the fundamental principle of FFA?
a rapid series of fundus images are acquired following IV injection of fluorescent agent sodium fluorescein (C20H10O5Na2)
What are 3 properties of fluorescein?
- organic
- water soluble
- dye
What does FFA aid visualisation of?
the choroidal and retinal vasculature
What light is fluorescein a) stimulated by b) does it emit?
- a) stimulated by blue light (490nm)
- b) emits green light (530nm)
What type of filters are used to acquire FFA images?
- blue excitation filters
- yellow-green barrier filters
What structure in the blood is FFA bound to and what proportion is bound?
plasma albumin - 70-85%
What structures metabolise and excrete sodium fluorescein and within what time frame is it excreted?
- metabolised by the liver
- excreted by the kidneys
in 24hours
What 2 things does visualisation of the fundus in FFA require?
- clear media
- dilated pupils
What are 4 indications for FFA?
- diagnosing chorioretinal vascular disease e.g. diabetic retinopathy, neovascular AMD
- diagnosing macular disease e.g. CSC (central serous chorioretinopathy)
- assessment of intermediate and psoterior uveitis
- planning of retinal laser procedures
What are 3 relative contraindications to FFA?
- previous history of severe reactions to fluorescein
- pregnancy
- lower doses of fluorescein advisable in renal impairment
What are 7 side effects of fluorescein?
- transient skin and urine discolouration
- extravasation of dye at injection site with local irritation/ thrombophlebitis
- nausea and vomiting
- pruritus
- vasovagal syncope (1 in 340)
- severe anaphylaxis (1 in 1900)
- fatal anaphylaxis (1 in 220 000)
What proportion of people experience vasovagal syncope in response to fluorescein?
1 in 340
What proportion of people experience severe anaphylaxis in response to fluorescein?
1 in 1900
What proportion of people experience fatal anaphylaxis in response to fluorescein?
1 in 220 000
How should the patient be prepared for FFA? 7 steps
- explain procedure
- risks and benefits
- formal consent
- check BP
- cannulate (medium to large bore vein)
- ensure resuscitation facilities inc crash trolley available
- seat patient at camera, adjust height for comfort + align
- ask patient to fix on fixation target
What should be done in the FFA process prior to fluorescein injection?
take colour and ‘red-free’ fundal photographs
What volume and concentation of fluorescein should be injected for FFA?
5mls 10%
When should photographs be taken after inejction with fluorescein dye?
- early rapid sequence photographs at about 1s intervals for 25-30s
- continue less frequent shots, alternating between the eyes for up to 5-10 minutes
- late images may be taken at 10-20 minutes
Why is it important to inform the FFA photographer which eye takes priority?
generally only possible to get good series of early shots from one eye due to the time it takes to move between eyes
What are 5 steps to reporting an FFA?
- report the red-free photo
- specify the phase
- note hyper- and hypofluorescence and any delay in filling
- note distinctive features (petalloid, smoke stack etc)
- note any change in area, intensity or fluorescence over time
How should FFA images be read?
sequentially, according to their phases: choroidal (pre-arterial), arterial, capillary, venous, and late
What are 6 types of hyperfluorescence seen in FFA?
- window defect
- leakage of dye
- pooling of dye
- staining of dye
- abnormal vessels
- autofluorescence (visible without dye)
What causes a window defect leading to hyperfluorescence in FFA?
RPE defect e.g. RPE atrophy, macular hole
What causes leakage of dye leading to hyperfluorescence in FFA at the macula?
cystoid macular oedema (CMO): petalloid appearance
other macular oedema
What is the appearance of CMO on FFA?
causes leakage of dye–> hyperfluorescence: petalloid appearance
What are 3 causes of leakage of dye leading to hyperfluorescence in FFA at the disc?
- papilloedema
- ischaemic optic neuropathy
- inflammation
What are 3 things that cause leakage of dye leading to hyperfluorescence in FFA elsewhere (i.e. not the macula or disc)?
- new retinal vessels
- vasculitis
- choroidal neovascularisation (CNV)
What are 2 things that can cause pooling of dye leading to hyperfluorescence in FFA and what are 2 examples?
Detachment of neural retina or RPE e.g.:
1. central serous chorioretinopathy
2. AMD
What are 4 things that can cause staining of dye leading to hyperfluorescence with FFA?
- drusen
- disc
- disciform scars
- sclera (seen if overlying chorioretinal atrophy/thinning)
What can cause abnormal vessels resulting in hyperfluorescence on FFA?
tumours e.g. haemangiomas, melanomas
What are 2 structures in the eye with autofluorescence, resulting in hyeprfluorescence on FFA?
- Disc drusen
- large lipofuscin deposits
What are 2 types of causes of hypofluorescence on FFA?
- transmission defects
- filling defects (circulation abnormalities)
Into what 3 groups can transmission defects resulting in hypofluorescence on FFA be grouped?
- preretinal
- inner retinal
- prechoroidal
What is a preretinal transmission defect on FFA?
blocks view of retinal and choroidal circulations
What are 2 examples of causes of preretinal transmission defects on FFA?
- media opacities esp. vitreous opacities: inflammation, haemorrhage, degenerative
- preretinal haemorrhage
How do inner retinal transmission defects result in hypofluorescence on FFA?
blocks view of capillary circulation, but larger retinal vessels are seen
What are 2 examples of causes of inner retinal transmission defects?
- dot and blot haemorrhages e.g. vein occlusion
- intraretinal lipid e.g. diabetic retinopathy
How can prechoroidal transmission defects lead to hypofluorescence on FFA?
blocks view of choroidal circulation but retinal circulation seen
What are 4 causes of prechoroidal transmission defects leading to hypofluorescence on FFA?
- subretinal haemorrhage
- pigment e.g. choroidal naevi, congenital hypertrophy of RPE (CHRPE), melanoma
- lipid
- lipofuscin
What are 4 causes of filling defects (i.e. circulation abnormalities) leading to hypofluorescence on FFA?
- retinal arteriolar non-perfusion (e.g. arterial occlusion)
- retinal capillary non-perfusion (e.g. ischaemia secondary to diabetes, vein occlusion)
- choroidal non-perfusion (e.g. infarcts secondary to accelerated hypertension etc.)
- disc non-perfusion (e.g. ischaemic optic neuropathy)
Under what circumstance is indocyanine green (ICG) angiography usually performed?
in association with FFA
What is ICG angiography used for?
used to study the choroidal circulation
What is ICG bound to in the blood and what proportion is this?
98% bound to serum proteins
How do the protein binding properties of ICG influence its properties as a fluorescent dye?
the serum proteins do not pass through choriocapillaris vessel fenestrations; the larger choroidal vessels are not obscured by early leakage of dye from this layer
What are the excitation and emission peaks of ICG?
excitation peak 810nm (infrared) and emission peak at 830nm (infrared)
Why is the use of long wavelength emitting ICG useful?
enhances depth penetration, especially in cases of retinal haemorrhage
What are 4 indications for ICG angiography?
- diagnosis of CNV not clearly visualised on FFA (e.g. extensive submacular haemorrhage or serous RPE detachments)
- identifying idiopathic polypoidal choroidal vasculopathy (IPVC) - esp pts with neovascular AMD appearing refractory to tx
- assessment of choroidal tumours + ocular inflammatory disease
- assessment of choroidal hyperpermeability prior to application of photodynamic therapy (PDT) in CSC
How is the ICG dye itself prepared?
ICG powder is mixed with aqueous solvent to make a solution of 40mg in 2ml
What are the steps to preparing and taking the images in ICG?
- red-free photo taken
- IV bolus given
- frequent images taken over first 3 min, then later images at 5, 10, 15, 20 and 30 min for example
What is a contraindication to ICG angiography?
pregnancy
What are 7 side effects of ICG angiography?
- nausea and vomiting
- sneezing and pruritus
- backache
- staining of stool
- vasovagal syncope
- severe anaphylaxis (1 in 1900)
What is the rate of severe anaphylaxis with ICG angiography?
1 in 1900
What time period is considered to correspond to the following periods?
* early phase
* early mid-phase
* late mid-phase
* late phase
- early phase: 2-60s
- early mid-phase: 1-3min
- late mid-phase: 3-15min
- late phase: 15-30min
What is seen in the early phase (2-60s) of ICG angiography?
prominent filling of choroidal arteries, which appear tortuous
What is seen in the early mid-phase (1-3min) of ICG angiography?
increased prominence of choroidal veins, which appear straight and drain towards the vortex vein in each quadrant
What is seen in the late mid-phase (3-15min) of ICG angiography?
diffuse hyperfluorescence due to diffusion of dye from the choriocapillaris
What is seen in the late phase (15-30min) of ICG angiography?
dye may remain in neovascular tissue after if has left in the choroidal and retinal circulations
Is iodine allergy a contraindication for ICG?
no - iodine is present throughout our bodies and is essential to life.
What are 3 types of causes of hyperfluorescence on ICG angiography?
- window defect
- leakage of dye
- abnormal blood vessels
What can cause a window defect in ICG angiography?
RPE defect
What can cause leakage of dye in ICG angiography?
CNV
IPCV: polyps and branching vascular network
What can cause abnormal blood vessels in ICG angiography?
choroidal haemangioma
What are 2 types of causes of hypofluorescence in ICG angiography?
- transmission defect
- filling defects (circulation abnormalities)
What is 1 major causes of a transmission defect in ICG angiography?
RPE detachment (hypofluorescent centrally)
How does the transmission defect caused by blood/pigment/exudate in IG angiography compare with the effect in FFA?
they cause less blockage than in FFA
What are 2 examples of caues of filling defects leading to hypofluorescence in ICG angiography?
- choroidal infarcts secondary to accelerated HTN, SLE
- choroidal atrophy e.g. atrophic AMD, some chorioretinal scars, choroideraemia
What technique can be used to measure retinal and choroidal blood flow?
quantitative angiography
What technique is quantitative angiography based on?
dye dilution techniques where concenration of fluorescein at a particular point is graphed over time
What scientific effect can be used to calculate ocular blood flow velocities?
measurement of Doppler effect
What measures are required to calculate absolute values for blood flow volume in retinal adn choroidal circulation?
measuring doppler effect, diameter of blood vessel
What are 2 examples of laser doppler devices developed to quantify ocular blood flow velocity?
- Canon Laser Blood Flowmeter
- Heidelberg Retina Flowmeter
How can spectral imaging be used for retinal oximetry?
measurement of light reflected from the retina at multiple walvelengths used to assess retinal oxygen saturation
What is an eample of a device used for retinal oximetry?
multispectral imaging device (Oxymap T1) used for research purposes
