Evaluation of foveal avascular zone alterations in diabetic retinopathy with optical coherence tomography angiography

Purpose : to describe alterations of foveal avascular zone(FAZ) in superficial capillary plexus layer evaluated with optical coherence tomography angiography ( OCT-A ). Methods : images from 72 patients affected by CME secondary to diabetes examined with SD-OCT (Spectralis OCT, Heidelberg Engineering, Germany or Cirrus 5000 OCT, Zeiss, Germany), En Face OCT and OCT-A (Optovue XR Avanti, Optovue, USA) at the Eye Clinic Department, Hôpital Intercommunal, Créteil, France, and at the University Eye Clinic of Cagliari, Italy, were retrospectively examined. The superficial capillary plexus OCT-A images and the corresponding EnFace OCT images, both acquired with the same automatic segmentation, were overlapped to compose RGB color images as red and green channels, respectively, using ImageJ software (National Institutes of Health, Bethesda, MD). Ischemic zones were evaluated by means of Optovue "No Flow" tool, which permits to quantify the cumulative no-flow areas. Results : OCT-A images of superficial capillary plexus demonstrate that FAZ has an oblong shape, with residual microvessels running through the area. It is surrounded by ancillary ischemic zones, as outlined by the overlapping of RGB color images. The average area of the FAZ is 0,8133 mm2 ( D.S. ± 0,070 ), the average surface of ancyllary regions is 0.053 mm2 ( D.S. ± 0,022 ), the average maximum diameter is 6,65 micron ( D.S. ± 0,065), the average minimum diameter is 5,39 micron (D.S. ± 0,024). FAZ arcade disruption occurs in 67% of patients, while 33% show no FAZ arcade interruption. FAZ arcade interruption is observed in different sectors of the arcade: 16% infero-temporal, 33% superior-temporal, 17% infero-nasal, 34% supero-nasal. Conclusions : RGB channels applied to OCT-A and en face OCT images allow a tridimensional visualization of macular capillaries, and to outline a detailed map of the capillary network. Moreover, it permits to appreciate small ischemic retinal areas and FAZ irregularities. It is a very useful tool to study evolution of diabetic retinopathy and treatment response.