Choroidal luminal and stromal areas and choriocapillaris perfusion are characterised by a non-linear quadratic relation in healthy eyes

Purpose To assess the associations among different optical coherence tomography (OCT) structural and angiography quantitative metrics used to characterise the choroid in healthy subjects. Methods In this cross-sectional study, macular structural OCT and OCT angiography (OCTA) images were acquired from healthy subjects. The main outcome measures were: (i) choriocapillaris (CC) flow deficits percentage (FD%), (ii) choroidal luminal (LA) and stromal (SA) areas and (iii) choroidal vascularity index (CVI), which was calculated as the LA divided by the total choroidal area. These measurements were generated using previously published algorithms and were separately computed in the foveal and extrafoveal regions. Results Eighty-five eyes from 85 subjects (44 males, 41 females) were included in the analysis. Mean±SD age was 47.9±22.4 years (range: 19.0 to 85.0 years). Linear regression analysis displayed no significant associations between CC FD% and other parameters (LA, SA and CVI). Importantly, non-linear regression analysis showed that the relations of LA and SA to CC FD% were all best fitted by a quadratic function. Compared with the linear models, the use of the quadratic function allowed a relative increase in the R2 coefficients. No significant non-linear associations were found between CC FD% and CVI. Conclusion Based on our models, changes in the luminal and stromal areas in the choroid lead to an initial increase in CC perfusion. Subsequently, further increases in LA and SA amounts are accompanied by a progressive increment in CC FD%.