## 3 Optical Nerve Diseases
### Glaucoma
This is consistent with the results of [PERSON] et al. [158], [PERSON] et al. [160], and [PERSON] et al. [151]. [PERSON] et al. [155] investigated peripillary VD in glaucoma patients using OCTA. They showed a reduction in peripapillary VD in areas corresponding to RNFL thinning on OCT scans and VF defect on Humphery perimetry. This vascular-functional correlation is explained by the fact that reduced vascular supply to retinal ganglion cells and their axons is the stage that precedes the death of ganglion supply. Therefore, OCTA detection of diminished vascular density is an early indicator of progression of the disease [163]. [PERSON] et al. [156] investigated peripapillary VD in 60 eyes with glaucoma and hemi-field VF defects using OCTA. A reduction was detected in the peripapillary VD that corresponds to the hemi-field VF defects in glaucomatous eyes that were either non-highlymyopic or highly myopic. Additionally, they found a reduction in the density of the optic disc vessel that corresponds to the hemi-field VF defects in non-highly myopic glaucomatous eyes, but not in highly myopic glaucomatous eyes. [PERSON] et al. [159] assessed peripapillary VD in 41 glaucomatous eyes with focal lamina crickprosa (LC) defect versus 41 glaucomatous eyes without LC defect. They revealed that reduction of peripapillary VD is greater in glaucomatous eyes with LC defect and that reduction of VD is most marked at the LC defect location. [PERSON] et al. [157] compared peripapillary VD among 43 eyes with exfoliation glaucoma (XFG), 33 eyes with exfoliation syndrome (XFS), 31 eyes with primary open angle glaucoma (POAG), and 45 control healthy eyes. They found that peripapillary VD decreases from the controls to the XFS to the POAG to the XFG progressively. [PERSON] et al. [160] investigated peripapillary VD and macular VD in 58 glaucomatous patients with hemi-field VF defect using OCTA. Authors found a reduction of VD in the affected hemi-retina when compared with the unaffected hemi-retina. In addition, the VD of the unaffected hemi-retina of glaucoma eyes is reduced when compared with VD of healthy control eyes. [PERSON] et al. [161] used OCTA to study the average change rate in macular VD in glaucoma patients. They studied eyes of 100 cases (30 glaucoma-suspect, 32 glaucomatous, 38 healthy). The results showed that the average macular VD reduction rate was significantly faster in glaucomatous eyes (\(-2:23\%/y\)) than in glaucoma-suspect (\(-0:87\%/y\)) than in healthy eyes (\(-0:29\%/y\)). A study conducted by [PERSON] et al. [162] used projection-resolved OCTA to study macular perfusion defects in 33 glaucoma patients. They found that the SCP is affected more than the DCP in glaucomatous eyes. This effect on the SCP in glaucoma is logical, as the SCP supplies the RNFL, part of the inner plexiform layer (IPL) and ganglion cell layer (GCL), the anatomic layers that the glaucoma affects the most. [PERSON] et al. [164] investigated the diagnostic significance of the density of vessels in different regions in OCTA images. They found that peripapillary VD is more specific than optic nerve VD or macular VD in diagnosis of glaucoma. [PERSON] et al. [165] conducted an OCTA-based comparison between the intrasession repeatability of peripapillary and density of macular vessel measurements in 65 eyes (35 glaucomatous, 30 normal). For every eye, authors used three macular scans and three ONH scans. The results showed that most measurements have similar repeatability for eyes that are either glaucomatous or normal. [PERSON] et al. [166] studied choroidal microvascular dropout (CMvD) prevalence in OCTA of 73 POAG eyes (32 with disc hemorrhage (DH), 41 without DH). Results observed a dropout in the choroidal microvascular of 17 eyes with DH (\(53:1\%\)) and 13 eyes without DH (\(31:7\%\)). [PERSON] et al. [167] conducted a comparative study using 46 eyes with glaucoma and studied the localization of retinal nerve fiber layer defects in red-free fundus photographs and OCT en-face images.