Recent updates in choroidal imaging biomarkers

The choroid, a highly vascularized tissue, supplies the outer retina and is responsible for other functions such as thermoregulation, secretion of growth factors, and possibly emmetropization. Choroidal changes, therefore, may play a role in various chorioretinal diseases. The recent surge in publications focusing on the choroid can be attributed to improvements in both resolution and field of view of optical coherence tomography and indocyanine green angiography. Advancements in imaging have transitioned from manual to semi-automated and now fully automated methods for qualitative and quantitative choroidal analysis. These qualitative parameters include choroidal vascular patterns and focal or diffuse changes in the vascular wall, either bulbosity or tortuosity. Quantitative parameters include choroidal thickness, volume, vascularity index, contour, three-dimensional vessel quantification, and blood flow measurements using laser Doppler holography. We discuss these qualitative and quantitative biomarkers in detail, i.e., the underlying principles, clinical use, changes in normal and disease states, and their limitations. This will provide invaluable insights to clinicians in understanding the choroidal changes in physiological and pathological states.