Indocyanine Green Angiography
Clinically, indocyanine green and fluorescein provide different information on the state of the choroid. Indocyanine green angiography is used to evaluate the choroidal circulation below the pigment epithelium of the retina whereas fluorescein imaging of the retinal circulation is obtained on the pigment epithelium.
Therefore, the two exams are complemented to evaluate the choroidal circulation related to macular diseases.
The main indication for indocyanine green angiography is for the diagnosis and therapy of patients with the "wet" form of age-related macular degeneration (AMD), especially when a choroidal polypoid vasculopathy is suspected, with vessels Abnormal choroids, usually manifested as exudative maculopathy with recurrent serous detachment, bleeding or both signs. As it is unknown whether this vasculopathy represents a different entity or is a variant of choroidal neovascularization secondary to AMD is still under study.
Indocyanin green angiography is the best test available to diagnose this pathology. It is usually a primary abnormality of the choroidal circulation in which a network of vessels terminates in polypoid or saccular dilations (such as an aneurysm) under the pigment epithelium.
Classification: there are two systems. The Japanese Study Group guidelines suggest that a "definitive" diagnosis can be made in the presence of high reddish-orange lesions protruding from the fundus examination that correspond to the choroidal dilatations that cause serous-hemorrhagic detachments and choroidal nodules, characteristic In indocyanine green angiography, showing early hyperfluorescence and clearing or disappearance of fluorescence in the late phases.3 A diagnosis of "probable" choroidal polypoid vasculopathy can be made only when an abnormal vascular branch is observed with indocyanine green .
The Everest Study states that choroidal polypoid vasculopathy can be diagnosed if, in addition to the presence of subretinal focal hyperfluorescence, at least one of the following angiographic or clinical criteria is met: vascular network, pulsatile polyps, nodular appearance when observed stereoscopically, presence of Hypofluorescent halos, orange subretinal nodules in color photos or association with massive submacular hemorrhage.
In the United States, choroidal polypoid vasculopathy occurs in 10% of choroidal neovascularization in white people and is more common among yellow and black people. Therefore, indocyanine green angiography should be considered in the following situations:
Choroidal neovascularization not responding to conventional anti-VEGF therapy. When the active component of the polypoid form is subfoveal, photodynamic therapy (PDT) is often useful.
Serous-hemorrhagic exudative detachment and major subretinal hemorrhages.
Unilateral exudative AMD with no signs of AMD (such as drusen) in the other eye.
It is worth remembering that choroidal polypoid vasculopathy can occur in the presence of classical choroidal neovascularization in fluorescein angiography.
Occult choroidal neovascularization
Indocyanine green leaks more slowly than fluorescein. Careful evaluation of the hidden choroidal membranes related to AMD have shown that there are two distinct forms of neovascularization. One demonstrates localized areas of intense hyperfluorescence or "hot" (no larger than 1 DD) that have an incidence of 29%. The other shows larger but discrete areas (about 1 DD) of hyperfluorescence but with less leakage, which are called plaques, with a lower incidence (8%). They can be indefinable when the borders cannot be well distinguished or if there is a hemorrhage that blocks (blocking) the identification of part of the neovascular membrane.
Indocyanine green angiography is very important because the medium and large choroidal vessels of the choroidal membrane can be detected. If more than one occult choroidal neovascularization area is observed, it is multifocal. Although fluorescein sometimes shows well-defined (classical) membranes better than indocyanine green, in many cases indocyanine green shows that, what is interpreted with fluorescein as a hidden membrane, it is actually A classic. Therefore, in dubious cases it is recommended to do the angiography with the two dyes.
The corneal neovascularization related to AMD damages and erodes the pigment epithelium, infiltrates the neurosensory space and communicates with the retinal circulation, which is common in the final stages of the discomfort healing.
However, it has been found that this situation is also possible in reverse. When angiomatous proliferation originates in the retina and extends into the subretinal space, it can communicate with the vessels of the choroid, known as angiomatous proliferation of the retina that can be confused with typical choroidal vascular proliferation. These differences may have been revealed with the aid of indiocyanin green angiography. There are three stages:
Phase I: proliferation involving intraretinal capillaries from the deep layers of the retina (intraretinal neovascularization).
Phase II: growth of retinal vessels within the subretinal space (subretinal neovascularization).
Phase III: when choroidal neovascularization is diagnosed clinically or angiographically. It may be accompanied by a vascularized detachment of the pigment epithelium. Chorioretinal anastomoses form between both circulations.
In cases of angiomatous retinal proliferation, fluorescein angiography is not very useful and with green indiocyanin green the choroidal circulation can be observed much better. Lesions are best diagnosed in the medium and late phases, being seen as more intense areas of hyperfluorescence as the dye leaks to the neighboring intraretinal tissues and into the subretinal space. The incidence of angiomatous proliferation of the retina is 20% of the cases.
Patients with angiomatous retinal proliferation present a similar picture to patients with neovascularization typical of AMD, although they tend to be older than 80 years with patients with the classic and occult variety. It is a bilateral problem and lesions occur in the juxtafoveal area. The most frequent clinical signs include retinal hemorrhages and prerretal detachments of the pigment epithelium, small and multiple intraretinal hemorrhages.
Indiocyanin green angiography allows the detection of occult neovascular membranes (87% of cases) under the retinal pigment epithelium and other neovascularization classes (polypoid, choreoetinal anastomosis, main vessel of the neovascular network, etc. Diagnostic imaging with Indocyanine green are used to better understand the choroid in non-neovascular diseases, especially those of inflammatory origin. Therefore indocyanine green angiography should be ordered prior to initiating the treatment of occult neovascularization, whether handled with antidote drugs -VEGF, photodynamic therapy or both.
- Yannuzzi LA, Ciardella A, Spaide RF, et al. The Expanding Clinical Spectrum of Idiopathic Polypoidal Choroidal Vasculopathy. Arch Ophthalmol 1997; 115: 478-485.
- Laude A, Cackett PD, Vithana EN, et al. Polypoidal Choroidal Vasculopathy and Neovascular Age-Related Macular Degeneration: Same or Different Disease? Prog Retin Eye Res. 2010; 29: 19-29.
- Koh A, Lee WK, Chen LJ, et al. Everest Study: Efficacy and Safety of Verteporfin Photodynamic Therapy in combination with Ranibizumab or Alone versus Ranibizumab Monotherapy in Patients with Symptomatic Macular Polypoidal Choroidal Vasculopathy. Retina 2012; 32 (8): 1453-1456.
- Arcacha MA. Angiography of the retina with fluorescein and indocyanine green. http://retinapanama.com/paginas/medicos/art-83.htm
- Wong T. When Should I Use Indocyanine Green Angiography? American Academy of Ophthalmology. Subspecialty Day 2013, Retina. Page 64-65.