A modified measuring method to investigate the choriocapillaris flow void of polypoidal choroidal vasculopathy with swept source optical coherence tomography angiography

Background: To propose a modified method to investigate the flow void of polypoidal choroidal vasculopathy (PCV) choriocapillaris. Methods: This paper involves a retrospective study. Included 30 PCV affect eyes, 30 old control eyes, 20 young control eyes, 15 affect eyes with anti-VEGF intravitreal injection treatment, and 8 fellow eyes of anti-VEGF intravitreal injection treatment group. After the choriocapillaris slab [10 mu m thick starting 30 mu m beneath to the retinal pigment epithelium (RPE)-fit reference] was extracted from macular optical coherence tomography angiography 6x6-mm scans, the flow void was segmented by the Phansalkar method. We analyzed the flow void sizes-frequency histogram in order to investigate the differences of flow void proportion between groups. Then we verified the differences between groups after anti-VEGF intravitreal injection treatment. Results: On the difference curve between the PCV group and Old control group, there was a peak appeared at the flow void sizes range from 900 to 1,125 mu m(2). The average number of flow void sizes from 900 to 1,125 mu m(2) was significantly higher in the Old control group than that in the Young control group (P<0.05) and there was no difference between the affect eyes group and the Old control group. The proportion of flow void sizes from 900 to 1,125 mu m(2) were remarkably higher in the affect eyes group compared to the Old control group (P<0.05), showing no difference between the Young control group and the Old control group. The average number of flow void sizes from 900 to 1,125 mu m(2) and the proportion of flow void sizes range from 900 to 1,125 mu m(2) were significantly higher in the treatment group after the treatment (P<0.05) and there was no difference in the fellow eyes of treatment group. The choroidal thickness was significantly reduced after the treatment of the treatment group (P<0.001), while the fellow eyes of the treatment group had no difference. Conclusions: Our method was specific for the pathological changes in choriocapillaris structures of PCV affect eyes, fellow eyes, and the affect eyes after anti-VEGF treatment.