Abstract
The choroid was poorly accessible to imaging investigation until the last decade of the last century. With the availability of more precise imaging methods such as indocyanine green angiography (ICGA) and, later, optical coherence tomography (OCT), enhanced depth OCT (EDI-OCT), and OCT angiography (OCTA), appraisal of choroidal inflammation has substantially gained in accuracy. This allowed to precisely determine which structures were touched in the different non-infectious choroiditis entities and made it possible to classify this group of diseases, ICGA signs, mainly hypofluorescent lesions, were identified and described. Previous publications have divided angiographic findings into two main sets of signs: (1) irregular “geographic” hypofluorescent areas corresponding to choriocapillaris non-perfusion and (2) round more regular, hypofluorescent dark dots more evenly distributed in the fundus corresponding to more deep choroidal stromal foci. These distinct findings allowed to subdivide and classify choroiditis into choriocapillaritis and stromal choroiditis. Additional signs were identified from EDI-OCT and OCTA examination supporting the classification of choroiditis into choriocapillaritis and stromal choroiditis. Results: Diseases involving principally the choriocapillaris included Multiple Evanescent White Dot Syndrome (MEWDS), Acute Posterior Multifocal Placoid Pigment Epitheliopathy (APMPPE), Idiopathic Multifocal Choroiditis (MFC), and Serpiginous Choroiditis (SC) as well as mixed forms. Diseases primarily involving the choroidal stroma included HLA-A29 Birdshot Retinochoroiditis (BRC), Vogt-Koyanagi-Harada disease (VKH), Sympathetic Ophthalmia (SO), and Sarcoidosis chorioretinitis (SARC). Thanks to new imaging investigations of the choroid, it is now possible to classify and understand the diverse clinicopathological mechanisms in the group of non-infectious choroiditis entities.
Highlights
Imaging exploration of the choroidal compartment used to be limited for inflammatory conditions before appropriate technologies became available
Fluorescein angiography (FA), principally offering information on the surface of the fundus, gives dynamic information but is not adapted for the choroid as the retinal pigmentary epithelium (RPE) blocks most of the rays in the visible spectrum of light, which is used in FA
optical coherence tomography (OCT) angiography (OCTA) contributed to image the inner choroid at the level of the choriocapillaris [10,11], but is ill-suited for more deeper parts of the choroid, studies with questionable practical implications have been published [12]. The drawbacks of these OCT methods reside in the fact that they only account for pathology in the posterior pole of the fundus [13]
Summary
Imaging exploration of the choroidal compartment used to be limited for inflammatory conditions before appropriate technologies became available. Echography using B-scan ultrasonography was one modality used to image inflammation of the choroid giving relatively useful information in the past on the structure, it was rather rough, lacking the needed precision for fine analysis OCT angiography (OCTA) contributed to image the inner choroid at the level of the choriocapillaris [10,11], but is ill-suited for more deeper parts of the choroid, studies with questionable practical implications have been published [12] The drawbacks of these OCT methods reside in the fact that they only account for pathology in the posterior pole of the fundus [13]. Indocyanine green angiography (ICGA) is characterised by two particular properties of the ICG molecule used in this procedure: (1) fluorescence at around 830 nanometres (nm) in the near infrared spectrum of light and (2) macromolecular behaviour [14]
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