## 2 Retinal Vascular Diseases
### Diabetic Retinopathy (DR)
#### 2.1.1 Detection of DR  
FAZ Enlargement  
Size and morphology of the FAZ is an important indicator of capillary perfusion status within the macula; it correlates with the grade of DR, and abnormalities of FAZ can sometimes indicate macular ischemia [33]. One of the various clinical applications of OCTA in DR is its ability to evaluate the shape and the size of the FAZ area. Several clinical studies ([PERSON] et al. [34], [PERSON] et al. [35], [PERSON] et al. [36], [PERSON] et al. [37], [PERSON] et al. [38], [PERSON] et al. [39]) reported enlargement of FAZ in diabetic patients versus normal healthy controls. Figure 1 shows enlargement of FAZ in DCP and SCP in a diabetic patient versus a normal control. [PERSON] et al. [34] found an enlargement of FAZ in the SCP in the healthy controls compared to eyes of patients of diabetic with DR and enlargement of FAZ in the DCP in the healthy controls compared to the eyes of diabetic patients with DR. [PERSON] et al. [20] found an enlargement of FAZ in the SCP in the healthy controls compared to the eyes of diabetic patients with DR.  
[PERSON] et al. [35] also found an enlargement of FAZ in the SCP in the healthy controls compared to the eyes of diabetic patients with DR and enlargement of FAZ in the DCP in healthy controls compared to the eyes of diabetic patients with DR. They concluded that the enlargement of the FAZ is statistically significant in the DCP at a rate of 5.1% per year. There was also enlargement of FAZ in the SCP, but it was not statistically significant. Figure 1: FAZ enlargement. (**a**) SCP for a normal subject, (**b**) DCP for a normal subject, (**c**) SCP for a diabetic patient, and (**d**) DCP for a diabetic patient. [PERSON] et al. [36] found significant enlargement of FAZ in the SCP in the healthy controls compared to the eyes of diabetic patients with DR and normal visual acuity (VA). They found further enlargement of FAZ in the diabetic patients with DR and reduced VA. They concluded that the enlargement of FAZ in diabetic patients with DR is negatively correlated with VA.  
[PERSON] et al. [37] found enlargement of the mean horizontal FAZ diameter in patients with DR versus normal healthy controls, as well as absence of normal orientation of the angle of the maximum FAZ diameter in DR patients due to the irregular configuration of the FAZ. [PERSON] et al. [40] recorded a significant correlation between enlargement of FAZ and poor visual prognosis in patients with DR. They also found that this positive correlation is modulated by patient's age, such that an increase in patient's age is associated with poorer vision. Table 1 lists the average areas of the FAZ in both normal and DR cases. FAZ Morphology  
Large individual variations can be detected by the evaluation of the FAZ area in both healthy [41; 42] and diabetic [43] eyes. Using OCTA, FAZ morphological parameters (a metric called circulatory index and axis ratio) were evaluated by [PERSON] et al. [44] in patients with diabetes versus healthy controls. In OCTA, acircularity index (irregularity of FAZ) and axis ratio (the ratio of the maximum and minimum axes of a best-fit ellipse fitted to the FAZ) were found helpful in distinguishing between control subjects and diabetic subjects with no DR, NPDR, and proliferative diabetic retinopathy (PDR). Higher axis ratio and acircularity index are considered statistical significant indicators of retinopathy advanced stage. A strong negative correlation was found between FAZ acircularity index and BCVA. The change in the FAZ acircularity index in DR patients is probably because of the capillary dropout. While quantification of FAZ area and shape has become increasingly common in the literature when characterizing sequelae of various retinal vascular diseases, there is another school of thought on the matter that calls into question the value of these metrics. One source of concern is that FAZ areas vary within the normal population.