*3.1.1 Optical coherence tomography angiography features of the optic nerve head in glaucoma*

Evaluation of the ONH microcirculation is commonly used to detect vascular damage in the glaucomatous eye, as there is a significant correlation between glaucoma severity and degree of VD loss in this region [9]. While the ONH of a healthy eye displays a dense microvascular network with no focal capillary dropout and a full RNFL thickness, the ONH microcirculation of a glaucomatous eye shows decreased perfusion and loss of the RNFL [9, 18].

In 2012, Jia et al. developed the SSADA algorithm to visualize and quantify ONH microcirculation [18]. In this pilot study, the SSADA results were applied to patients with early glaucoma to detect ONH perfusion abnormalities. The researchers found that ONH flow index and VD in patients with early glaucoma were significantly reduced compared to healthy controls. Furthermore, the ONH perfusion defects preceded VF changes, aiding in the early detection of disease.

Four years later, Chen et al. used OMAG-based OCTA to evaluate ONH blood vessels and perfusion and found that ONH perfusion decline was significantly correlated to the presence of structural and functional defects as well as disease severity [30]. Recently, Eslami et al. showed that OCTA ONH parameters can also discriminate between stages of glaucoma. Their cross-sectional investigation of patients with moderate and advanced glaucoma found that the VD of the inferior hemifield of the ONH area had the best performance in discriminating POAG stages [33].
