Early effects of viper envenomation on retina and optic nerve blood flow: An optical coherence tomography angiography study.

In this study, the early retinal and optic nerve blood flows of patients exposed to Viper bite were evaluated with non-invasive optical coherence tomography angiography (OCTA) and compared with healthy controls. The retinal and optic disc OCTA data of 31 victims of viper bite (group S) without systemic envenomation clinical symptoms and 31 healthy controls (group C) were compared. Only patients with early signs of envenomation were included in the study. Optical coherence tomography angiographies were performed with RTVue XR Avanti with AngioVue software. Vascular densities in the whole image, foveal, parafoveal regions at the superficial and the deep capillary plexus segments were acquired and statistically analyzed. The flow area parameters were measured in the superficial retinal capillary plexus, deep retinal capillary plexus, outer retinal capillary plexus, and choriocapillaris layers of the macula in 1-mm and 3-mm diameter areas. The peripapillary flow areas were measured for the optic nerve head, vitreous, radial peripapillary capillary (RPC), and choroid in a 4.50-mm diameter area. Foveal and parafoveal thicknesses were also measured and compared. The average hospital admission time of the patients in group S was 1.24 ± 0.75 (0.50-3.00) hours. Age (p = 0.103) and gender (p = 0.714) were similar in both groups. Superficial (p = 0.010), deep flow areas (p = 0.034), and superficial parafoveal vascular density (p = 0.001) were significantly reduced in group S compared to group C. The outer retinal flow area (p < 0.001) increased significantly in group S. Nerve head flow area (p = 0.035), one of the optic disc flow areas, was found to be decreased in group S. Notably, foveal (p < 0.001) and parafoveal (p = 0.003) thicknesses and superficial (p = 0.001) and deep (p < 0.001) foveal vascular densities were greater in group S. Compared to group C, the superficial (p = 0.009) and deep (p = 0.009) foveal flow areas in the central foveal area with a diameter of 1 mm increased significantly in group S. Viper venom may cause blood flow changes in the retina and optic disc and an increase in retinal thickness in the early period although there are no signs of systemic envenomation.