Choroidal Vascularity Index: An In-Depth Analysis of This Novel Optical Coherence Tomography Parameter

Abstract

Remarkable improvements in optical coherence tomography (OCT) technology have resulted in highly sophisticated, noninvasive machines allowing detailed and advanced morphological evaluation of all retinal and choroidal layers. Postproduction semiautomated imaging analysis with dedicated public-domain software allows precise quantitative analysis of binarized OCT images. In this regard, the choroidal vascularity index (CVI) is emerging as a new imaging tool for the measurement and analysis of the choroidal vascular system by quantifying both luminal and stromal choroidal components. Numerous reports have been published so far regarding CVI and its potential applications in healthy eyes as well as in the evaluation and management of several chorioretinal diseases. Current literature suggests that CVI has a lesser variability and is influenced by fewer physiologic factors as compared to choroidal thickness. It can be considered a relatively stable parameter for evaluating the changes in the choroidal vasculature. In this review, the principles and the applications of this advanced imaging modality for studying and understanding the contributing role of choroid in retinal and optic nerve diseases are discussed. Potential advances that may allow the widespread adoption of this tool in the routine clinical practice are also presented.

Keywords: choroidal imaging biomarkers; choroidal vascularity index; optical coherence tomography; retinal imaging.

Figure 1

Choroidal vascularity index (CVI) calculation with binarization of enhanced-depth imaging (EDI) spectral domain optical coherence tomography (SD-OCT) image. Choroidal boundaries were traced to identify the total choroidal area (yellow lines) (A). The image was binarized using Niblack’s auto-local threshold (B). The color threshold tool was used to select the dark pixels, representing the luminal area (yellow lines) (C). The CVI is calculated dividing luminal area by total choroidal area.

Figure 2

Choroidal vascularity index evaluation in a patient with multiple evanescent white dot syndrome. (A) In the acute stage, OCT shows ellipsoid zone disruption and a CVI of 69.3%. (B) In the healed stage, OCT shows normalization of the ellipsoid zone and a CVI decreased to 67.3%.

Figure 3

Choroidal vascularity index, calculated by the means of automated algorithm in a 56-year-old man with chronic central serous chorioretinopathy (CSC), before (A,B) and 3 months after (C,D) half-dose full-fluence photodynamic therapy, was 58.7% and 54.4%, respectively.

Figure 4

Choroidal vascularity index calculated with the OCT image binarization algorithm in a patient with geographic atrophy (A) and in an age-matched healthy subject (B) was 61.3% and 65.2%, respectively.

Figure 5

Choroidal vascularity index measurement in a patient with arteritic anterior ischemic optic neuropathy (A) and a patient with nonarteritic anterior ischemic optic neuropathy (B). (A) CVI was 65.1% in the patient with arteritic anterior ischemic optic neuropathy. (B) CVI was 68.3% in the patient with nonarteritic anterior ischemic optic neuropathy.