View source for Medicine:Indocyanine green angiography

{{short description|Diagnostic procedure}}
{{Infobox medical intervention |
  Name        = Indocyanine green angiography|
  Image       = LDHvsICG (cropped).jpg|
  Caption     = Choroidal blood flow revealed with indocyanine green angiography|
  ICD10       = |
  ICD9        = {{ICD9proc|95.11}} |
  MeshID      = |
  OtherCodes  = |
}}
'''Indocyanine green angiography''' ('''ICGA''') is a diagnostic procedure used to examine [[Biology:Choroid|choroid]]al blood flow and associated pathology. [[Chemistry:Indocyanine green|Indocyanine green]] (ICG) is a water soluble cyanine dye which shows [[Biology:Fluorescence|fluorescence]] in near-infrared (790–805&nbsp;nm) range, with peak spectral absorption of 800-810&nbsp;nm in blood.<ref name="AAO-ICGA">{{cite web |title=Indocyanine Green Angiography |url=https://www.aao.org/bcscsnippetdetail.aspx?id=a8a39222-9001-4811-a8d2-e062c967a84b |website=www.aao.org}}</ref><ref name="Khurana">{{cite book |last1=Khurana |first1=AK |title=Comprehensive ophthalmology |publisher=Jaypee, The Health Sciences Publisher |isbn=978-93-5152-657-5 |page=460 |edition=6th |chapter=Ocular therapeutics|date=31 August 2015 }}</ref> The near infrared light used in ICGA penetrates ocular pigments such as [[Chemistry:Melanin|melanin]] and [[Chemistry:Xanthophyll|xanthophyll]], as well as exudates and thin layers of sub-retinal vessels.<ref name="Kanski">{{cite book|last1=John F|first1=Salmon|title=Kanski's clinical ophthalmology : a systematic approach|publisher=Elsevier|year=2020|isbn=978-0-7020-7711-1|edition=9th|page=431|chapter=Uveitis}}</ref> Age-related macular degeneration is the third main cause of blindness worldwide, and it is the  leading cause of blindness in industrialized countries.<ref name="WHO">{{cite web |title=Priority eye diseases |url=https://www.who.int/blindness/causes/priority/en/index7.html |archive-url=https://web.archive.org/web/20060322164140/http://www.who.int/blindness/causes/priority/en/index7.html |url-status=dead |archive-date=March 22, 2006 |website=www.who.int}}</ref> Indocyanine green angiography is widely used to study [[Medicine:Choroidal neovascularization|choroidal neovascularization]] in patients with exudative age-related macular degeneration.<ref name="AMDBook" /> In nonexudative AMD, ICGA is used in classification of [[Medicine:Drusen|drusen]] and associated subretinal deposits.<ref name="AMDBook" />

==Indications==
Indications for indocyanine green angiography include:
* Choroidal neovascularisation (CNV):<ref name="Khurana" /> Indocyanine green angiography is widely used to study [[Medicine:Choroidal neovascularization|choroidal neovascularization]] in patients with exudative age-related macular degeneration. In ICGA, CNV is seen as hyperflourescent spot or plaque.<ref name="Kanski" /> It is also useful in diagnosing and classifying CNV associated to serous pigment epithelial detachments in Nonexudative macular degeneration.<ref name="AMDBook" />
* Idiopathic [[Medicine:Polypoidal choroidal vasculopathy|polypoidal choroidal vasculopathy]] (IPCV)<ref name="Khurana" />
* Pigmented choroidal melanomas<ref name="Khurana" />
* Choroidal haemangioma:<ref name="Khurana" /> ICGA can be used to differentiate choroidal haemangioma from other intraocular tumors.<ref name="Ryan" />
* Choroiditis:<ref name="Khurana" /> In multifocal choroiditis, lesions are visualized as hypoflourescent spots.<ref name="Ryan" />
* Chorioretinopathy: In [[Medicine:Central serous chorioretinopathy|Central serous chorioretinopathy]], using ICGA multifocal areas of choroidal hyperpermiability can be visualized.<ref name="Ryan" /> In birdshoot chorioretinopathy, lesions appear as symmetrical round or oval hypoflourescent spots.<ref name="Ryan" /> ICGA allows better visualization of lesions in serpiginous chorioretinopathy, punctate inner chorioretinopathy, acute zonal occult outer retinopathy etc.<ref name="Ryan" /> In [[Medicine:Multiple evanescent white dot syndrome|multiple evanescent white dot syndrome]], numerous hypoflourescent spots can be visualized using ICGA.<ref name="Kanski" />
* Pigmented epithelial detachment<ref name="AAO-ICGA" />
* Retinal angiomatous proliferation (RAP)
* Chorioretinal atrophy: ICGA help evaluating different stages of chorioretinal atrophy.<ref name="Ryan" />
* Anterior uveitis: ICGA is rarely indicated in anterior uveitis, but it might be used to find out associated choroidal pathology.<ref name="Kanski" />
* Stargardt disease: Numerous hypoflourescent spots are seen in ICGA.<ref name="Kanski" />
* [[Medicine:Angioid streaks|Angioid streaks]]: ICGA can be used for diagnosing angioid streaks and their associated ocular pathologies.<ref name="POS">{{cite book |last1=Creig S |first1=Hoyt |last2=David |first2=Taylor |title=Pediatric ophthalmology and strabismus. |date=January 2012 |publisher=Saunders/Elsevier |isbn=9780702046919 |page=524 |edition=4th}}</ref>
* [[Medicine:Vogt–Koyanagi–Harada disease|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.<ref name=":0">{{Cite book|title=Albert & Jakobiec's principles and practice of ophthalmology|publisher=Saunders/Elsevier|others=Albert, Daniel M., Miller, Joan W. (Joan Whitten), Azar, Dimitri T.|year=2008|isbn=978-1-336-22997-6|edition=3rd|location=Philadelphia|oclc=489078723}}</ref>
* [[Medicine:Sympathetic ophthalmia|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.<ref name=":0" />

==Procedure==
Fundus camera-based indocyanine green angiography techniques and scanning laser ophthalmoscope-based indocyanine green angiography techniques are there.<ref name="ento" /> 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.<ref name="Ryan" /> In case of iodine allergy, instead of ICG, iodine-free dye [[Chemistry:Infracyanine green|Infracyanine green]] should be used.<ref>{{Cite book |last=Dithmar |first=S. |url=https://www.worldcat.org/oclc/288578300 |title=Fluorescence angiography in ophthalmology |date=2008 |publisher=Springer Medizin Verlag |others=Frank G. Holz |isbn=978-3-540-79401-1 |location=Heidelberg |pages=3 |oclc=288578300}}</ref>

To perform test, [[Biology:Pupil|pupil]] should be dilated. The dye is injected through the antecubital vein as [[Medicine:Bolus|bolus]].<ref name="CMO" /> Images are taken in several second intervals until the retinal and choroidal circulations are maximally hyperfluorescent.<ref name="ento" /> Then for first few minutes, take photos at approximately 30 to 60 second intervals. Pictures taken are classified under three phases:<ref name="mukh">{{cite book |last1=PK |first1=Mukherjee |title=Clinical examination in ophthalmology |year=2016 |publisher=Elsevier |isbn=978-81-312-4463-0 |edition=2nd }}</ref>
# Early phase at 60 seconds: large choroidal arteries and veins are highlighted in this phase.<ref name="Gologorsky">{{Cite book |url=https://www.worldcat.org/oclc/1259320518 |title=Principles of ocular imaging : a comprehensive guide for the eye specialist |date=2021 |others=Daniel Gologorsky, Richard B. Rosen |isbn=978-1-63091-600-8 |location=Thorofare, NJ |oclc=1259320518|page=93}}</ref>
# 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.<ref name="Gologorsky"/>
# Late phase at 15–30 minutes: in this phase hyperfluorescent lesions appear bright against the dark background.<ref name="Gologorsky"/> The choroidal neovascularization are best detected in this phase.<ref name="Gologorsky"/>

==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.<ref name="AAO-ICGA" /> Choroidal neovascularization is better visualized by ICGA, than fluorescein angiography.<ref name="AMDBook">{{cite web |title=Diagnostic usefulness of indocyanine green angiography (ICGA) in age-related macular degeneration (AMD) |url=https://amdbook.org/content/diagnostic-usefulness-indocyanine-green-angiography-icga-age-related-macular-degeneration-am |website=www.amdbook.org |language=en}}</ref> The patient toleration is also better compared to FFA.<ref name="CMO">{{cite book |title=Comprehensive manual of ophthalmology |publisher=Jaypee Brothers |isbn=978-93-5025-175-1 |page=122 |chapter=History, Clinical Examinations and Techniques of Examination|date=15 June 2010 }}</ref>

==History==
Physical and physiological properties of indocyanine green dye were first described by Fox and Wood, in 1960.<ref name="NCBI-ICG">{{cite journal |last1=Owens |first1=S L |title=Indocyanine green angiography. |journal=The British Journal of Ophthalmology |date=March 1996 |volume=80 |issue=3 |pages=263–266 |doi=10.1136/bjo.80.3.263 |pmid=8703866 |pmc=505439 |issn=0007-1161}}</ref> Indocyanine green angiography was developed by Kodak Research Laboratories for determining cardiac output. In 1968, Kogure et al. performed intra-arterial choroidal absorption angiography using indocyanine green dye in monkeys.<ref name="JOP">{{cite journal |last1=Earl A. |first1=Choromokos |last2=Noble J. |first2=David |title=The Beginnings of Indocyanine Green Angiography |journal=Journal of Ophthalmic Photography |volume=16 |page=70 |url=https://cdn.ymaws.com/www.opsweb.org/resource/resmgr/history/16-2-09.pdf}}</ref> In the year 1969, using ICGA, Kogure and Choromokos studied cerebral circulation in a dog. In 1971, Hochhimer replaced color film with black and white infrared film. First human ICG angiogram was of carotid artery. First intravenous ICGA in human eye was performed by Flower and Hochheimer in 1972.<ref name="CMO" /><ref name="Ryan">{{cite book |last1=Andrew P. |first1=Schachat |title=Ryan's retina Vol 1 |isbn=978-0-323-40197-5 |pages=46–76 |edition=6th |chapter=Clinical applications of diagnostic indocyanine green angiography|date=31 May 2017 }}</ref> In 1986 Hayashi et al. used infrared-sensitive video camera to perform ICGA.<ref name="ento">{{cite web |last1=Themes |first1=U. F. O. |title=Indocyanine Green Angiography |url=https://entokey.com/indocyanine-green-angiography/ |website=Ento Key |date=10 July 2016}}</ref> In the year 1992, Guyer et al. introduced the use of high resolution (1024 × 1024) digital imaging system coupled with infrared video cameras to produce better high resolution images.<ref name="Radio">{{cite web |last1=Themes |first1=U. F. O. |title=Clinical Applications of Diagnostic Indocyanine Green Angiography |url=https://radiologykey.com/clinical-applications-of-diagnostic-indocyanine-green-angiography/ |website=Radiology Key |date=21 December 2015}}</ref>

==See also==
* [[Engineering:Fundus photography|Fundus photography]]
* [[Medicine:Fluorescein angiography|Fundus fluorescein angiography]]
* [[Medicine:Eye examination|Eye examination]]

==References==
{{reflist}}
{{Medical imaging}}

[[Category:Diagnostic ophthalmology]]

{{Sourceattribution|Indocyanine green angiography}}