Evaluation of putative differences in vessel density and flow area in normal tension and high-pressure glaucoma using OCT-angiography

Purpose: To evaluate the putative differences in terms of vessel density and flow area between control (CTRL), high-pressure glaucoma (HPG) and normal tension glaucoma (NTG) subjects at macular and peripapillary level. To assess the correlation between Visual Field Index (VFI), the stage of glaucoma, and optical coherence tomography angiography (OCT-A) parameters.Material and methods: In this pilot, prospective study 46 eyes of 46 glaucomatous patients (19 NTG+ 27 HPG) and 25 control eyes (CTRL) of 25 subjects were recruited. All patients underwent a complete ophthalmologic examination and visual field testing. A 3 x 3mm volumetric macular scan (Angio Retina [3.0]) and a 4.5 x 4.5mm diameter peripapillary scan (Angio Disc [4.5]) were performed in the right eye using RTVue-XR Avanti (Optovue, Inc.) OCT-A.Results: Groups were homogeneous for age (P = 0.784) and gender (P = 0.623). Among the evaluated optic nerve head (ONH) and macular OCT-A parameters, ONH whole image (P< 0.001), inside disc (P = 0.021), peripapillary (P< 0.001), ONH flow area (P< 0.026), macula whole image (P<0.001), fovea (P<0.001), parafovea (P<0.001) showed a significant difference when CTRL group was compared to HPG group at the post hoc test. Similarly, ONH whole image (P<0.001), inside disc (P = 0.005), peripapillary (P<0.001), ONH flow area (P<0.026), macula whole image (P<0.001), FOVEA (P<0.001), parafovea (P<0.001) showed a significant difference were CTRL were compared to NTG group. On the contrary, no significant difference was found when NTG and HPG groups were compared. Age was not significantly correlated with any of the OCT-A parameters. The stage of the disease showed a high, significant, correlation with ONH whole image (r = -0.81; P<0.0001), inside disc (r = -0.42; P<0.0001), peripapillary (r = -0.81; P<0.0001), RNFL (r = -0.79; P<0.0001), macula whole image (r = 0.56; P<0.0001), fovea (r = -0.78; P<0.0001) and parafovea (r = 0.67; P<0.0001). On the contrary, VFI showed a high, significant, correlation with ONH whole image (r = 0.77; P<0.0001), inside disc (r = 0.39; P = 0.0018), peripapillary (r = 0.713; P<0.0001), RNFL (r = 0.63; P<0.0001), macula whole image (r = -0.39; P = 0.0007), fovea (r = 0.60; P<0.0001) and parafovea (r = -0.52; P<0.0001).Conclusions: Our data support the usefulness of the OCT-A in the common clinical practice for diagnosis, staging, evaluating the progression of the disease as well as for better understanding of its pathogenic mechanisms.