Structure of polypoidal choroidal vasculopathy studied by colocalization between tomographic and angiographic lesions

Purpose To investigate the structure of polypoidal choroidal vasculopathy (PCV) by tomographic localization of the branching vascular network and late geographic hyperfluorescence. Design Observational case series. Methods We examined 34 eyes with PCV by simultaneous indocyanine green angiography (ICGA) and spectral-domain optical coherence tomography (OCT) imaging. The margin of the branching vascular network and the late geographic hyperfluorescence on ICGA was colocalized on OCT, in a point-to-point manner, using innate software. The large vessels within the branching vascular network were also colocalized on OCT. Results Late geographic hyperfluorescence on ICGA was noted in 30 eyes. The extent of late geographic hyperfluorescence was larger than that of branching vascular network in 12 eyes. In the remaining eyes, the extent was the same. A double-layer sign on OCT, which consisted of two hyper-reflective lines, representing the retinal pigment epithelium and Bruch membrane, was noted in 29 eyes. In all 28 eyes exhibiting both late geographic hyperfluorescence and the double-layer sign, the extent of late geographic hyperfluorescence matched exactly the extent of double-layer sign on OCT. In 7 of 34 eyes, the thickness of the subretinal pigment epithelial space over the Bruch membrane was too thin to accommodate the large vessels of the branching vascular network. Although the double-layer sign showed mild reduction in area after photodynamic therapy, its general configuration was maintained. Conclusions Late geographic hyperfluorescence on ICGA corresponds with the double-layer sign on OCT in eyes with PCV. Our observations suggest that the double-layer sign consists mainly of fibrous tissue harbored by the branching vascular network, and late geographic hyperfluorescence may originate from the staining of tissue.