Long-term effect of photodynamic therapy on choroidal vascularity index versus choroidal thickness as biomarkers for chronic central serous chorioretinopathy.

Objective: To investigate the long-term impact of half-fluence photodynamic therapy (PDT) on chorioretinal architecture in chronic central serous chorioretinopathy (cCSCR) through novel choroidal vascularity index (CVI) versus previously established subfoveal choroidal thickness (SFCT).

Methods: This post-hoc analysis included prospectively collected swept-source optical coherence tomography (SS-OCT) images of a total of 29 cCSCR and fellow eyes (FE), acquired before, one and 12 months after PDT. CVI, total choroidal area (TCA), luminal area (LA) and stromal area (SA) were calculated using validated binarization technique. Central macular thickness (CMT), SFCT and subretinal fluid (SRF) were assessed. Longitudinal changes following PDT and associations between all parameters were investigated.

Results: CVI, TCA, LA, SFCT and CMT significantly decreased at month 1 (all p < 0.001). From month 1 to 12, CVI (p < 0.001) and LA (p = 0.01) increased but remained significantly lower than at baseline (p = 0.001 and p < 0.001). SFCT and CMT remained stable (all p = 1.0). SA and all FE parameters showed no significant changes at any time point. Comparing affected and FE, there were significant CVI differences at baseline (p < 0.001), month 1 (p = 0.01) and 12 (p < 0.001). SRF was significantly associated with higher CVI (p < 0.001), LA (p = 0.031), SFCT (p = 0.038).

Conclusion: Half-fluence PDT significantly affects choroidal architecture, with sustained CVI and SFCT reductions 12 months post-treatment. Use of CVI as both a treatment response and disease activity marker is merited. There is a large discrepancy between CVI and SFCT, suggesting they each represent different anatomic responses. CVI proves to be a more specific and reliable CSCR biomarker than previously established SFCT.