CLINICAL TECHNIQUES - Flourescein and ICG, Flashcards
What are the contraindications to ICG? (5)
- Pregnancy
- Seafood Allergy (not in FFA)
- Iodide Allergy (not in FFA)
- Kidney Failure
- Liver Disease (not in FFA)
What are the contraindications to FFA? (4)
- Previous allergy to fluorescein
- Breastfeeding (not in ICG)
- Kidney failure
- Pregnancy (relative contraindication)
What are the side effects of 5-FU during glaucoma filtration surgery?
Ischaemic blebs
Hypotony
Suprachoroidal haemorrahge
What are the wavelengths of sodium flourescein?
Absorbs blue light - 465-495nm
Emits green light - 520-530nm
Usually 10%
How much flourescein is bounded to plasma protein?
How much is ICG boudned to plasma protein?
80% bound to proteins
98% bound to proteins
Where can flourescein distribute to?
Readily diffuses through the choriocapillaries through fenestrations..
Does not diffuse through retinal vascular endothelium (in RNFL) and RPE due to blood retinal barrier - if there are breakages in RPE or neovascularisations, can pass here.
What is the mechanism of FFA?
White light passes through cobalt blue excitation filter and reach retina and reflect back (blue and green light will reflect back)
Barrier filter blocks blue light and only allows yellow/green light to exit and give flourescein image.
What are the different phases of FFA?
Choroidal: 10-12 seconds after injection (choroidal flush due to dye leaking through choriocapillaries from long PCAs
Arterial: 1-3 seconds after choroidal phase - can see neovascularisation of the disc
AV phase: Demonstrates laminar flow.
Late phase: Useful to highlight CMO, CSR or occult CNVMs
Later staining of optic disc is normal.
What are the different abnormalities seen in FFA?
(4)
Leakage - increasing in hyperflourescence over time.
1. Incompetence of inner/outer Blood retinal barriers
2. Neovascularisation: Defective inner barrier
3. Defective choroidal circulation (AMD)
Window defect: Unmasking of normal choroidal flourescence –> seen early.
1. RPE atrophy
Late Hyperflourescence due to dye staining
1. Drusen
2. Disciform scars
Pseudo-auoflouresence - overlap in transmission of excitation and barrier filters.
When is ICG used?
More information about choroidal circulation
as ICG can penetrate through overlying RPE
- Occult/poorly defined CNVM
- Polypoidal CNV
- Fibrovascular PEDs
- Medial opacities/vitreous haemorrhage
- Photophobic patients (can’t see infrared but can see visible light)
- Inflammatory disease: occult choroidal disease
At what wavelengths does ICG absorb and flouresce?
Absorption: 790-805nm
Emission: 770-880nm
Within infrared range of wavelengths and so can penetrate overlying RPE and overlying haemorrhages.
What are the main side effects of ICG/FFA.
FFA: discoloured urine and skin
ICG: discoloured stool as ICG is excreted by hepatobiliary system
WHen does the early venous phase begin in relation to the choroidal phase?
5 seconds after choroidal phase
Why is the macula darker in arteriovenous phase? (3)
- Xantophyllic pigment
- More pigment in RPE cells
- Absence of capillaries in avascular region of fovea.
Which arteries fill earlier in arterial phase, nasal or temporal?
Nasal arteries fill earlier
Are choroidal arteries straight or tortuous? Are choroidal veins straight or tortuous?
Choroidal arteries: tortuous
Choroidal veins: straight
How much does sodium fluorescein weigh?
376Da
How quickly is flourescein metabolised by the liver and excreted by the kidneys?
Within 24 hours
When are the phases of ICG?
- Early phase
- Early mid phase
- Late mid phase
- Late phase
- Early - 2-60 seconds
- Early mid phase - 1-3 minutes
- Late mid-phase: 3-15 minutes
- Late phase: 15-30 minutes
How much does ICG weigh? How much does flourescein weigh?
FLourescein: 376 daltons
ICG: 775 daltons
What are the differences in SLO imaging vs colour fundus camera imaging?
- Higher contrast in SLO
- Lower spatial and temporal resolution in colour fundus photos
3.
What is the source of autoflouresence?
Lipofuscin in the RPE is source of background autofloureseence of retina –> byproduct of phagocytosis of outer segments in the RPE.
What does autoflouresence refer to?
Emission of intrinsic flouresence by substance subsequent to stimulation by excitation energy
What colour light is used for auto-fluorescence?
Green.
Hypoflourescence in all phases of angiography of ICG indicative of which conditions?
Permanent: Atrophic lesions
Reversible: White dot syndromes (MEWDS, APMPPE)
Hypoflourescence until intermediate phase of ICG which then become isofluorescent or hyperfluoresent in the late phase are indicative of what conditions?
- Space-occupying lesions beneath the choriocapillaris
- Granulomatous inflammation (VKH, sympathetic ophthalmia, sarcoid, tuberculosis, birdshop chorioretinopathy)
The Scanning Laser Ophthalmoscopy machine used to detect autoflourescence –> 1. Uses what wavelength for excitation?
488nm
Which lesions are typically hyperfluorescent on FFA but hypofluorescent on ICG?
PEDs.
The auto-flourescence camera reduces interference from which structure?
Lens
