This document provides an overview of indocyanine green angiography (ICGA). It discusses that ICGA uses the near-infrared dye indocyanine green to image the choroidal and retinal vasculature. The dye is injected intravenously and imaged over time using a fundus camera with infrared filters. ICGA allows better visualization of the choroid compared to fluorescein angiography. It has applications in diagnosing conditions like age-related macular degeneration, choroidal neovascularization, and tumors. The document outlines the properties, principles, procedures, indications, limitations and comparisons to fluorescein angiography of ICGA.

1. Indocyanine Green
Angiography
By:
Anu Mushyakhwo
M. Optometry
Ansal University, Gurugram

2.  Introduction
 Properties
 Principle
 Indications
 Contraindications
 Difference in FFA and ICG
 Advantages
 Adverse Effects
 Phases of ICGA
 Procedure
 Limitations

3.  ICG dye is a water soluble tri-carbocyanine dye, primarily bound
to globulins that absorbs and emits fluorescence in infra red
spectrum of light
 Indocyanine green Angiography uses ICG dye to image choroidal
and retinal circulations.
Done using fundus camera with infrared filter or Laser Scanning
Ophthalmoscopy (SLO)

4. Fluorescence:
 Luminescence that is maintained only by continuous
excitation. Property of certain molecules to emit light
energy of longer wavelength when stimulated by a
shorter wavelength.

5.  water-soluble, tricarbocyanine dye
 contains less than 5% sodium iodide in order to increase its
solubility
 ICG has a half life of 150 to 180 seconds
 absorbs light at 805nm and emits fluorescence at 835nm
 98% protein – binding
 ICG fluorescence is only 1/25th or 4% that of fluorescein
 is secreted unchanged by the liver into the bile without renal
excretion
 there is no renal excretion and it does not cross the placenta.

6.  the principle of fluorescence imaging used in ICG
angiography (ICGA) is simple: illuminate the tissue of
interest with light at the excitation wavelength (about 750
to 805 nm) while observing it at longer emission
wavelengths (over 800 nm; Figure).
 To create a simple ICGA device, only a couple of filters are
needed in addition to a proper camera and a light source,
which can be quite small and suitable even for portable use
.
 The filters are needed to prevent the mixing of the
excitation (strong) and fluorescing (weak) rays to sum at the
sensor.
 Without the filters, the weak fluorescence image cannot be
seen among the strong reflection of the excitation light.

7. Lightsource Φ0
ΦS
Sensor
I0
Eb
Lens
R Ic
Filter,Fs
T
Fs
T
Fc Filter,Fc
Is It
Tissue Tt Et
E
F,t
BloodandICG
Φ
F
,C
Hb
,C
ICG Ee EF
Fluorescence
FIGURE 4: The principle of fluorescence imaging. The radiation from the light source is filtered by a high-pass filter, Fs, to
remove the fluorescent wavelengths. The blood and ICG suspension under a tissue absorbs the excitation wavelengths and
emits in fluorescent band. The emitted light is received by the sensor through a low-pass filter, Fc, to remove the excitation
lightreflected fromthesource.
FIGURE: The principle of fluorescence imaging. The radiation from the
light source is filtered by a high-pass /excitation filter, Fs, to remove the
fluorescent wavelengths. The blood and ICG suspension under a tissue
absorbs the excitation wavelengths and emits in fluorescent band. The
emitted light is received by the sensor through a low-pass /barrier filter,
Fc, to remove the excitation light reflected from the source.

8.  Polypoidal choroidal vasculopathy (PCV)
 Choroidal Neovascularization
 Exudative age-related macular degeneration (AMD)
 Posterior uveitis.
 Choroidal tumors
 RPE detachment
(ICGA is superior to FFA in imaging and diagnosis of the
above conditions)
 Chronic central serous chorio-retinopathy: often
difficult to interpret areas of leakage on FA. ICGA
shows choroidal leakage and the presence of dilated
choroidal vessels.
 Breaks in Bruch membrane (When FFA is
contraindicated)

9.  contraindicated in liver disease
 in patients with a history of a severe reaction to any
allergen
 moderate or severe asthma
 significant cardiac disease
 unsure for the pregnant women (safety in
pregnancy has not been established)

11.  Study of choroidal vasculature which is of limited in FFA due
to RPE blockage
 Near-infrared light utilized penetrates melanin, xanthophylls,
exudates and layers of sub-retinal blood better than the
conventional fluorescein dye making this test more suitable
 Infrared is scattered less than visible light, thus suitable in
eyes with media opacities
 98% ICG molecules bound to protein, thus remaining in the
blood vessels.
 ICG fluorescence can be imaged even in the presence of
considerable blood
 Photophobic patients tolerate ICGA better thanFFA
 ICGA accurately measures the size of hidden choroidal
neovascular membrane(CNVM).

12.  mild nausea, vomiting
 anaphylaxis, approximately equal incidence to
FA
 serious reactions are exceptionally rare
 ICG contains iodide and so should not be given
to patients allergic to iodine or possibly
shellfish
Iodine-free preparations such as infracyanine
green are available

13.  The technique is similar to that of FA.
 There is an increased emphasis on the the later images (up to
about 45 minutes) than with FA
 A dose of 25–50 mg in 1–2 ml water for injection is used.

14. A. Early – up to 60 seconds post-injection
B. Early mid-phase – 1–3 minutes
C. Late mid-phase –3–15 minutes
D. Late phase – 15–45 minute
Interpretation: (Same as FFA):
 Hypocyanescence: Blockage and filling defects
 Hypercyanescence: Leakage, staining, pooling and window defects

15.  showing prominent choroidal arteries

16.  showing greater prominence of choroidal
veins as well as retinal vessels

17. • choroidal vessels fading but retinal vessels
are still visible

18.  showing hypofluorescent choroidal vessels and
gradual fading of diffuse hyperfluorescence

19. FIGURE: ICG Comparison of FA and ICGA in imaging mouse retinal and
choroidal vasculature.

20. The left picture shows the choroidal neovascularization with
abnormal branching on either side but the right picture of FA shows
light leakage only.

21. Figure: Polypoidal Choroidal Vasculopathy

22.  the choriocapillaris cannot be imaged
separately with ICGA (retinal vessels are also
imaged)
 although superior to FFA in the imaging of
occult CNVM, ICGA may underestimate the
size of the CNVM

23.  Wide-angle angiography
 Overlay technique
 Digital stereo imaging
 Digital subtraction ICGA

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