Does OCT Angiography of Macula Play a Role in Glaucoma Diagnostics?

Purpose: To assess vascularity of the macular area in patients with glaucoma using optical coherence tomography angiography (OCT-A) and evaluate the role of its examination in early glaucoma diagnosis. Materials and Methods: Thirty-eight eyes of patients with the early stage of primary open-angle glaucoma (POAG), 27 eyes of patients with the advanced and far-advanced stages of POAG, and 22 eyes of age-matched healthy subjects were examined using spectral-domain OCT-A (SD-OCT-А) (RtVue xR Avanti with the AngioVue software, San Jose, CA, USA) in order to measure retinal thickness and angio flow density (AFD) retina in macula (an area bounded by a circle with a diameter of 3 mm), inсluding fovea and parafovea regions (superficial and deep) of the inner retinal layers. The AFD disc and peripapillary flow density were measured in optic nerve head (ONH) and 750-μm-wide elliptical annulus extending from the optic disc boundary. Retrobulbar blood flow parameters, including ophthalmic artery (OA), central retinal artery (CRA), short posterior ciliary arteries (PCAs), central retinal vein (CRV), and vortex veins (VV), were measured by color doppler imaging (CDI). The average thickness of the ganglion cell complex (avg GCC), retinal nerve fiber layer (RNFL), and choroid, as well as the focal loss volume (FLV) and global loss volume (GLV) of GCC were measured by means of SD-OCT. Automated perimetry was performed using Humphrey perimeter (Carl Zeiss Meditec, Dublin, CA, USA). Corneal-compensated intraocular pressure (IOPcc) and corneal hysteresis (CH) were determined using ocular response analyzer. Mean ocular perfusion pressure (MOPP) was calculated by measuring IOP and arterial blood pressure (BP) immediately prior to OCT and using formula: MOPP = (2/3 diastolic BP + 1/3 systolic BP) × 2/3 – IOP. Statistical analysis was performed using SPSS version 21 and MASS library in the R language. As a measure of the parameter’s importance in distinguishing patient groups, a value of the adjusted standardized statistic of the Mann-Whitney test (z-value) and an area under the receiver operating characteristic (ROC) curve (AUC) were used. Results: Although all structural parameters and indices of retrobulbar blood flow were reduced in early glaucoma as compared to the normal controls, the following parameters were the main discrepancy criteria when discriminating these patient groups: macular vascular density-AFD Retina Superficial Whole En Face (z=3.86, p<0.0001; AUC 0.8 (0.69-0.90) and macular thickness in the inferior sector ILM-RPE (z=3.86, p<0.0001; AUC 0.8 (0.69-0.91)). In discriminating early glaucoma from the advanced and far advanced stages of the disease, the most useful were: AFD Disc Peripapillary Inferior Temporalis (z=5.61, p<0.0001; AUC 0.94 (0.86-1.0)) and mean flow velocity in CRA (z=4.16, p<0.0001; AUC 0.81 (0.69-0.92)). Conclusions: The present study revealed the significance of OCT-A for the early diagnosis of glaucoma and the priority of the investigation of the macular microcirculation and its thickness in the inferior sector. These results allow understanding the cause of the early involvement of the macular inner layers in the pathological process in glaucoma.