2.3. Morphologic Correlation Study and Diagnosis Criteria

AMD neovascular activity, PCV subtype analysis, and BVN diagnosis criteria were all assessed from SS-OCTA obtained using a deep ranging imaging (DRI) OCT Triton. Three fifty-micron slabs were shifted and analyzed around the appropriate layer over and under the RPE. OCTA software within a commercially available device that operates at 70.000 A-scans per second to acquire OCTA volumes was used for all patients, allowing visualization of both retinal and choroidal flow and structure, based on split-spectrum amplitude decorrelation angiography. At first, the initial diagnosis made at clinic and the neovascular activity of AMD and PCV were assessed using multimodal imaging with FFA, ICGA, and SS-OCTA (examiner A). Then, SS-OCTA images were analyzed by a second independent expert operator (examiner B), blinded to all other multimodality images, which determined whether patients had AMD or PCV and assessed neovascular activity. Both examiners were retina specialists.

CNV activity in AMD patients was assessed using Coscas' criteria in exudative AMD using OCTA. According to his classification, active lesions present with at least one of the following criteria (Figures 1(a) and 1(b)): a wheel shape, a dense branching pattern, anastomosis and loops, a peripheral arcade, sprouting capillaries, and/or peripheral halo [10, 11]. On the other hand, quiescent lesions (Figures 2(a) and 2(b)) have a long and filamentous shape, loose branching patterns, a dead-tree aspect, and lack of loops, peripheral arcade, and halo.

Active choroidal new vessel on OCT-A (a) according to Coscas' criteria: wheel shape, dense branching pattern, anastomosis and loops, peripheral arcade, sprouting capillaries, and black peripheral halo. B-scan OCT showing activity of retrofoveal CNV (b).

Quiescent (long-lasting) choroidal new vessel on OCT-A (a) according to Coscas' criteria: long and filamentous shape, loose radial branching pattern, dead-tree aspect, and lack of loops. B-scan OCT showing fibrotic CNV scar (b).

PCV diagnosis was based on Tan et al.'s classification, which differentiates PCV into 3 subtypes by performing a combination of FFA and ICGA: type A is defined by the presence of a polyp with interconnecting channels on ICGA, type B is a polyp with BVN without leakage on FFA, and type C is a polyp with BVN that presents with late leakage on FFA [12]. Criteria for the establishment of BVN diagnosis included shape of the lesion, branching pattern, the presence or absence of anastomoses and loops, morphology of vessel termini, and the presence or absence of a perilesional hypointense halo [10]. Moreover, neovascular activity criteria for polyps included the presence of black holes, hypo/hypersignals, loops, and halos. Finally, BVN was described according to OCTA characteristics as dense, very dense (bush-shape), loose (dead-tree shape), pseudopod-like, and anastomoses.