Choroidal vascularity index as a measure of vascular status of the choroid: Measurements in healthy eyes from a population-based study

Abstract

The vascularity of the choroid has been implicated in the pathogenesis of various eye diseases. To date, no established quantifiable parameters to estimate vascular status of the choroid exists. Choroidal vascularity index (CVI) may potentially be used to assess vascular status of the choroid. We aimed to establish normative database for CVI and identify factors associated with CVI in healthy eyes. In this population-based study on 345 healthy eyes, choroidal enhanced depth imaging optical coherence tomography scans were segmented by modified image binarization technique. Total subfoveal choroidal area (TCA) was segmented into luminal (LA) and stromal (SA) area. CVI was calculated as the proportion of LA to TCA. Linear regression was used to identify ocular and systemic factors associated with CVI and subfoveal choroidal thickness (SFCT). Subfoveal CVI ranged from 60.07 to 71.27% with a mean value of 65.61 ± 2.33%. CVI was less variable than SFCT (coefficient of variation for CVI was 3.55 vs 40.30 for SFCT). Higher CVI was associated with thicker SFCT, but not associated with most physiological variables. CVI was elucidated as a significant determinant of SFCT. While SFCT was affected by many factors, CVI remained unaffected suggesting CVI to be a more robust marker of choroidal diseases.

Figure 1. Image binarization for choroid with normal choroidal thickness.

(A) Original SD OCT image. (B) 1.5 mm segmentation block of the subfoveal choroidal area. (C) Segmented OCT image using modified image binarization approach. (D) Overlay of region of interest created after image binarization was performed on the SD OCT image.

Figure 2

Distribution of subfoveal choroidal thickness (A) and choroidal vascularity index (B) across the population.

Figure 3. Bland Altman plots of total choroidal area and luminal area.

(A) and (B) shows intra- and inter- rater reliability for total choroidal area respectively. (C) and (D) shows intra- and inter- rater reliability for luminal area respectively. For intra-rater reliability, the difference was calculated by the 1st measurement minus the 2nd measurement. Pink dashed line represents regression line of difference between 1st and 2nd measurements. For inter-rater reliability, the difference was calculated by the grader 1 measurement minus the grader 2 measurement. Pink dashed line represents regression line of difference between the two graders measurements.