Indocyanine green angiography
From Wikipedia, the free encyclopedia
| Indocyanine green angiography | |
|---|---|
.jpg) Choroidal blood flow revealed with indocyanine green angiography | |
| ICD-9-CM | 95.11 |
Indocyanine green angiography (ICGA) is a diagnostic procedure used to examine choroidal blood flow and associated pathology. Indocyanine green (ICG) is a water soluble cyanine dye which shows fluorescence in near-infrared (790–805 nm) range, with peak spectral absorption of 800-810 nm in blood.[1][2] The near infrared light used in ICGA penetrates ocular pigments such as melanin and xanthophyll, as well as exudates and thin layers of sub-retinal vessels.[3] Age-related macular degeneration is the third main cause of blindness worldwide, and it is the leading cause of blindness in industrialized countries.[4] Indocyanine green angiography is widely used to study choroidal neovascularization in patients with exudative age-related macular degeneration.[5] In nonexudative AMD, ICGA is used in classification of drusen and associated subretinal deposits.[5]
Indications for indocyanine green angiography include:
- Choroidal neovascularisation (CNV):[2] Indocyanine green angiography is widely used to study choroidal neovascularization in patients with exudative age-related macular degeneration. In ICGA, CNV is seen as hyperflourescent spot or plaque.[3] It is also useful in diagnosing and classifying CNV associated to serous pigment epithelial detachments in Nonexudative macular degeneration.[5]
- Idiopathic polypoidal choroidal vasculopathy (IPCV)[2]
- Pigmented choroidal melanomas[2]
- Choroidal haemangioma:[2] ICGA can be used to differentiate choroidal haemangioma from other intraocular tumors.[6]
- Choroiditis:[2] In multifocal choroiditis, lesions are visualized as hypoflourescent spots.[6]
- Chorioretinopathy: In Central serous chorioretinopathy, using ICGA multifocal areas of choroidal hyperpermiability can be visualized.[6] In birdshoot chorioretinopathy, lesions appear as symmetrical round or oval hypoflourescent spots.[6] ICGA allows better visualization of lesions in serpiginous chorioretinopathy, punctate inner chorioretinopathy, acute zonal occult outer retinopathy etc.[6] In multiple evanescent white dot syndrome, numerous hypoflourescent spots can be visualized using ICGA.[3]
- Pigmented epithelial detachment[1]
- Retinal angiomatous proliferation (RAP)
- Chorioretinal atrophy: ICGA help evaluating different stages of chorioretinal atrophy.[6]
- Anterior uveitis: ICGA is rarely indicated in anterior uveitis, but it might be used to find out associated choroidal pathology.[3]
- Stargardt disease: Numerous hypoflourescent spots are seen in ICGA.[3]
- Angioid streaks: ICGA can be used for diagnosing angioid streaks and their associated ocular pathologies.[7]
- Vogt–Koyanagi–Harada disease (VKH): ICGA is useful in diagnosing VKH. In VKH, delay in filling of the choriocapillaris along with larger choroidal vessel perfusion and multiple hypofluorescent spots are visible with ICGA.[8]
- Sympathetic ophthalmia: Sympathetic ophthalmia is a bilateral, granulomatous form of uveitis. In sympathetic ophthalmia, numerous dark spots may be visible during the intermediate phase of ICGA.[8]
- Acute idiopathic blind spot enlargement syndrome, to detect hypofluorescent spots around the optic disc and arcades.[9]
Procedure
Fundus camera-based indocyanine green angiography techniques and scanning laser ophthalmoscope-based indocyanine green angiography techniques are there.[10] The concentration of indocyanine green dye may vary according to instrument used. For fundus cameras, 25 ml ICG dissolved in 5 ml solvent is used, it may be increased to 50 ml in patients with poorly dilated pupil and high pigmentation.[6]
To perform test, pupil should be dilated. The dye is injected through the antecubital vein as bolus.[11] Images are taken in several second intervals until the retinal and choroidal circulations are maximally hyperfluorescent.[10] Then for first few minutes, take photos at approximately 30 to 60 second intervals. Pictures taken are classified under three phases:[12]
- Early phase at 60 seconds: large choroidal arteries and veins are highlighted in this phase.[13]
- Mid phase at 5–15 minutes: in this phase choroidal vasculature become less distinct and more diffuse, and hyperfluorescent lesions appear bright against the fading background.[13]
- Late phase at 15–30 minutes: in this phase hyperfluorescent lesions appear bright against the dark background.[13] The choroidal neovascularization are best detected in this phase.[13]
Advantages over fluorescein angiography
Indocyanine green angiography has many advantages over commonly used fundus fluorescein angiography (FFA). Because of its protein-binding properties, its leakage from choriocapillaries is less and thus it will remain longer in choroidal vessels compared to fluorescein dye.[1] Choroidal neovascularization is better visualized by ICGA, than fluorescein angiography.[5] The patient toleration is also better compared to FFA.[11]
