The choroid is an intricate, highly vascular organ affected by a multitude of ocular and systemic diseases. Detailed structural analysis of the choroid using reliable parameters has tremendous implications in unveiling the pathomechanisms and understanding the progression of various ophthalmic pathologies, for both research and clinical purposes.
Studying the choroid is a tedious process, particularly due to its physical inaccessibility and complex angioarchitecture. Histopathological studies have established our fundamental knowledge by successfully delineating the various choroid layers, but the usage of post-mortem samples brought about limitations such as fixation induced shrinkage/artefacts and the inability to analyze longitudinal changes in vivo. The development of techniques such as fundus fluorescein angiography and indocyanine green angiography have provided clinicians with a means to study choroidal structure in living patients. However, angiography is an invasive procedure with dye related complications and operator dependency, rendering it less favorable as a research tool. With the advent of optical coherence tomography (OCT), a fast and non- invasive imaging modality with high resolution, we are now able to visualize cross sectional choroidal anatomy in real time. Researchers have attempted to achieve reproducible quantification of choroidal structure on OCT images, using biomarkers such as ‘choroidal thickness’ (CT), but the results have been inconsistent.
Our group has developed a new biomarker named ‘choroidal vascularity index‘ (CVI), defined as the ratio of total vascular luminal area (LA) to total choroidal area (TCA), computed by segmenting and binarizing OCT images using the public domain software, Fiji Image J (http://imageJ.nih.gov/ij/). A detailed protocol can be found in our previous studies. CVI provides specific information about the choroidal vasculature and is believed to be more accurate and repeatable. Since its proposal in the letter to the editor of American Journal of Ophthalmology in 2016, CVI has become a widely accepted research tool, with consistent findings leading to over numerous publications in peer reviewed journals. CVI has the potential as a practical tool for monitoring, diagnosing and prognosticating ocular diseases, with significant implications on clinicians’ therapeutic decision making.
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