Background: Although photodynamic therapy (PDT) has become the standard treatment for central serous chorioretinopathy (CSC), its mechanism of action remains unclear. It is assumed that PDT induces short-term choriocapillaris (CC) occlusion and long-term choroidal vascular remodeling. In this paper, we describe the short-term CC changes induced by Half-Dose PDT (HD-PDT) in chronic CSC using optical coherence tomography-angiography (OCTA). Methods: This is a prospective interventional case series. Chronic CSC eyes underwent Spectral-Domain OCT, Fundus Autofluorescence, FA, ICGA (Heidelberg Spectralis, Heidelberg, Germany) and OCTA (RTVue XR Avanti with AngioVue; Optovue Inc., Fremont, CA, USA) before HD-PDT, with follow-up after one hour, one week, and one month. Vascular changes after PDT were analyzed within the CC layer. The CC vessel density was defined as the percentage of an area occupied by flow pixels, using Image J software to obtain measurements by applying a grey level threshold. All pixels with a grey level above the threshold were considered as indicators of blood flow. Results: 20 eyes of 19 patients were included. At baseline the mean CC vessel density was 94.87 ± 2.32%. It significantly differed from the density at 1 week and 1 month (92.79 ± 3.16% and 95.55 ± 2.05%, p
< 0.001, respectively), but not with values at 1 h (94.8 ± 2.28%, p
= 0.516). Conclusions: CC vessel density was significantly reduced at 1 week as compared with baseline, suggesting a possible short-term effect of PDT on CC perfusion. After 1 month however, the CC vessel density was even higher than the baseline, probably due to a CC recovery. OCTA seems to be useful in the visualization of CC vessels and in confirming the mechanism of action of PDT treatment in eyes with chronic CSC.
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