## 2 Retinal Vascular Diseases
### Retinal Vein Occlusion
[40], [PERSON] et al. [126], [PERSON] et al. [115]) reported that the enlargement of FAZ is significantly correlated with poor visual prognosis in RVO patients. [PERSON] et al. [40] reported that this negative correlation is modulated by patient age such that an increase in patient age correlates with poorer vision. [PERSON] et al. [125] reported that poor visual prognosis is directly proportional to the size of FAZ in the SCP but not in the DCP. Several clinical studies ([PERSON] et al. [127], [PERSON] et al. [115], [PERSON] et al. [128]) have studied the relationship between retinal perfusion and visual prognosis in eyes with RVO after ME resolution using anti-VEGF therapy. They reported a significant positive correlation between pre-treatment retinal perfusion and visual acuity at last follow up. Thus, OCTA is able to provide visual prognostic information for patients with RVO. Using OCTA, [PERSON] et al. [129] studied the relationship between morphological parameters (axial ratio and acircularity index) of the FAZ and BCVA in eyes with BRVO. Results demonstrated that acirculatory index is not significantly correlated to BCVA in RVO. However, axial ratio (also called axis ratio) is significantly correlated to BCVA. Their finding suggests that the FAZ's morphological characteristics are more valuable visual prognostic indicators than the FAZ size alone in RVO eyes. Collateral vessels in the retina tend to arise after BRVO more frequently than they happen after CRVO. Collaterals are enlarged, existing capillaries that bypass venous obstruction that is driven by hemodynamic and hydrostatic forces. Usually, these vessels develop within weeks of RVO [130]. Collateral vessels course through DCP but not in the SCP, which supports the serial arrangement of the DCP and SCP, with venous drainage predominantly coursing through the DCP [131]. [PERSON] et al. [132] used OCTA to study the location of the collateral vessels that are associated with BRVO. They are curvilinear, dilated channels that connect veins across the horizontal raphe or veins on opposite sides of an occluded venous segment inside the same hemisphere of the retina. This conforms with the findings of [PERSON] et al. [133] that the collateral vessels are located in the DCP, representing retinocnoroidal anastomosis starting from the superficial retinal capillaries and reaching the choriocapillaris and choroidal vessels to bypass the site of occlusion. With BRVO eyes, [PERSON] et al. [134] used OCTA to analyze collateral vessels and how they are associated with visual outcomes and ME. They found that collaterals were observed more frequently in eyes with major BRVO or ischemic BRVOS. Furthermore, one-third of the collaterals were found to leak fluid, and MAs were found inside all leaky collaterals. In eyes with collaterals, ME resolves quicker than in eyes that do not have collaterals; however, no significant difference was found. While average baseline central retinal thickness (CRT) is significantly higher in eyes with collaterals, the presence of collateral vessels appears to have no effect on visual outcomes. One of the major complications of ischemic RVO is neovascularization of the retina, which takes the form of neovascularization of the disc (NVD) or neovascularization elsewhere (NVE). Retinal ischemia can even drive the formation of NV in the anterior segment of the eye, causing neovascular glaucoma (NVG), a particularly aggressive form of glaucoma [135]. NV is highly abnormal, and these vessels can bleed spontaneously, causing vitreous hemorrhage and sudden vision loss, or they can scar, causing tractional retinal detachment. An OCTA study by [PERSON] et al. [21] has analyzed NVE growth in an eye with hemi-CRVO. They found that OCTA can clearly visualize NVE growth and its detailed microvasculature. Identifying NV on OCTA is an indication for initiating or continuing anti-VEGF treatment or beginning panretinal photocoagulation. Development of collateral vessels is not an indication for anti-VEGF treatment.