Choroidal Biomarkers: A Repeatability and Topographical Comparison of Choroidal Thickness and Choroidal Vascularity Index in Healthy Eyes

Abstract

Purpose: Choroidal thickness (ChT) and choroidal vascularity index (CVI) represent two important metrics in health-, disease-, and myopia-related studies. Wide-field swept-source optical coherence tomography (OCT) provides improved and extended imaging and extraction of choroidal variables. This study characterizes the topography and repeatability of these parameters in healthy eyes.

Methods: Swept-source OCT volume scans were obtained on 14 young adult patients on three separate days. ChT and CVI were automatically corrected for image magnification and extracted for different enface regions within an extended ETDRS grid of 10 mm diameter. Topographical distribution, correlation to ocular length, and intersession repeatability of both choroidal parameters were assessed.

Results: CVI showed little fluctuation between subfields, unlike ChT, which demonstrated thinning toward the peripheral choroid (coefficients of variation 5.92 vs. 0.89). ChT showed a consistent negative correlation with axial length (ρ = -0.05 to -0.61), although this was only statistically significant in the inner superior subfield (P = 0.02). There was no consistent or significant relationship between CVI and axial length or between CVI and ChT. The repeatability of CVI measurements (3.90%-5.51%) was more consistent between scan regions than ChT measurements (10.37-20.33 µm).

Conclusions: CVI values were consistent across the central 10 mm of the retina, while ChT reduced with eccentricity. The repeatability of both parameters is similar to the effect size reported in many studies using the choroid as a biomarker, which should be considered in the interpretation of findings.

Translational relevance: This study provided normative as well as metrological information for the clinical interpretation of ChT and CVI in health and disease.

Keywords: OCT; choroidal thickness; choroidal vascularity index.

Figure 1.

Extended ETDRS grid, showing the optic nerve head exclusion zone for a right eye. The ring diameters are 1 mm, 3 mm, 6 mm, and 10 mm.

Figure 2.

Output of the CVI algorithm for an example participant: (a) ChT segmentation as ROI. (b) Calculated number of vessel pixels. (c) CVI map without ETDRS grid. (d) CVI map with overlaying ETDRS grid, adjusted for image magnification. The white area of the ONH was excluded from analysis.