Role of the choroidal vascularity index in branch retinal vein occlusion (BRVO) with macular edema

Abstract

Purpose: To assess choroidal vasculature changes in eyes with branch retinal vein occlusion (BRVO) and macular edema (ME) using the choroidal vascularity index (CVI) and evaluate the effectiveness of CVI as a prognostic biomarker.

Methods: 35 patients with monocular BRVO and ME were analyzed retrospectively. Luminal and stromal areas in choroids of swept-source optical coherence tomography were calculated using the image binarization technique. The CVI was calculated as the ratio of the luminal to total choroidal area. The CVI of BRVO and ME eyes were compared with that of the unaffected fellow and post anti-vascular endothelial growth factor (VEGF) injected eyes. A regression analysis was performed on the choroidal parameters, logMAR visual acuity (VA) two years post disease onset and central macula thickness (CMT).

Results: The CVI of BRVO and ME eyes was significantly lower than the fellow and post-injected eyes (p<0.05). The regression analysis showed a strong association between two years after logMAR VA and the CVI of fellow eyes (R2 = 0.433, p<0.001). Remarkable correlations were observed in the CVI and subfoveal choroidal thickness of BRVO and ME eyes (R2 = 0.189, 0.155, respectively, p<0.05). The CMT of diseased eyes were also significantly associated with the CVI of unaffected fellow eyes (R2 = 0.113, p<0.05).

Conclusions: The alteration of CVI in BRVO and ME suggests that choroidal vasculature might be affected by extracellular fluid shift and VEGF changes. The fellow eye CVI could be a useful supplementary prognostic biomarker.

Fig 1. The choroidal vascularity index (CVI) measuring process with swept-source optical coherence tomography.

The total choroidal area (TCA) was determined using the polygon selection tool in ImageJ software (A). Following image binarization using the Niblack auto local threshold tool, the stromal area (SA) within the selected TCA was highlighted. A distinction was set between the SA (the yellow part) and the luminal area (LA; the black part) (B). The CVI was calculated as the ratio of LA to TCA.

Fig 2. The choroidal vascularity index (CVI) and subfoveal choroidal thickness (SFCT) were measured to compare the branch retinal vein occlusion (BRVO), unaffected fellow, and post anti- vascular endothelial growth factor (VEGF) injected BRVO eyes.

(A) The CVI of the BRVO eyes was significantly decreased compared to the unaffected fellow and post-injected eyes (all p<0.05). (B) The SFCT of the post anti-VEGF injected eyes was significantly decreased compared to the BRVO eyes (p<0.05), with no significant change between the BRVO and unaffected fellow eyes found (p = 0.447; Wilcoxon matched-pairs signed-rank test).

Fig 3. The linear regression analysis between the choroidal parameters and logarithm of the minimum angle of resolution scale (logMAR) visual acuity measured two years post the disease onset.

The correlation between the choroidal vascularity index (CVI) of unaffected fellow eyes and the central macula thickness (CMT) of BRVO eyes. The R² and p-values are presented. (B) The CVI of unaffected fellow eyes reveal the most prominent correlation value and a significant p-value; (A), (C) With the significant p-values, remarkable correlations are presented in the CVI and subfoveal choroidal thickness (SFCT) of the eyes with BRVO. (D) The CVI of unaffected fellow eyes shows a significant association with the CMT of diseased eyes.