## 10 OCTA in Nonexudative MNV in AMD  
Previous studies have demonstrated that MNV can present without clinical sign of exudation. In the 1970s, histopathological studies pointed out the presence of what is now known as type 1 MNV in patients without any hemorrhage or exudation [111; 112]; later, [PERSON] et al. reported that ICGA was able to detect subclinical MNV not viewable with FA, by the presence of hyperfluorescent plaque with late staining, in the fellow eyes harboring soft drusen [113]. [PERSON] et al. detected on FA and ICGA type 1 MNV that had not developed intraretinal or subretinal exudation visualizable on OCT for at least 6 months, and they called this form treatment-naive quiescent neovascularization [10]. In 2016, [PERSON] et al. observed in patients with previously diagnosed neovascular AMD in one eye and asymptomatic iAMD in the contralateral eye the presence on ICGA of MNV without exudation and subsequently confirmed by OCTA [12]. Nonexudative MNV can be found both in iAMD and GA [12; 13; 14; 30; 114]. Nonexudative MNVs were described also in other retinal diseases such as pachy choroid, large colloid drusens, and angioid streaks [115; 116; 117]. [PERSON] et al. determined that OCTA has a good sensitivity and specificity for nonexudative MNV detection in eyes with iAMD, thus representing a valid diagnostic tool [114]. Several studies compared the ability of detecting MNV of SD-OCTA and SS-OCTA demonstrated that SS-OCTA provides better image quality and a more accurate representation of MNV than SD-OCTA [30; 31]. In iAMD, nonexudative MNVs usually present on OCTA as irregular, without visible-core, with a well-defined margin and foveal-sparing vessel networks, even if sometimes, they do not present a detectable core vessel, and it was hypothesized that this could represent a protective factor against increased activity [113] (Figure 4). They are usually located in the subfoveal/perifoveal area [114]. As mentioned above, [PERSON] et al. described nonexudative MNV in GA using OCTA, and this MNV showed different characteristics from those in iAMD [110]. OCTA in GA has a lower detection rate than in iAMD, which is probably because small MNV are more difficult to differentiate from choroid due to the low contrast between MNV and choroidal vessels in the absence of RPE and CC or due to their slow flow [110]. Nonexudative MNVs in GA show irregular-shaped high flow with well-defined margin networks without a visible core, and they present vessel arteriolization with few or without visible fine capillaries; they are usually found bordering the atrophic area [110]. The prevalence of nonexudative MNV was evaluated with OCTA by different groups, particularly in the contralateral eyes of patients with unilateral exudative AMD [13; 14; 15]. [PERSON] et al. [13] and [PERSON] et al. [14] reported a prevalence of 14.4% and 13.2% respectively at baseline of eyes with iAMD and GA, while [PERSON] et al. [15] found a prevalence of 7.9%. [PERSON] et al. analyzed 644 eyes from 399 consecutive patients with unilateral or bilateral GA secondary to AMD and identified 73 eyes from 71 patients (11%) with nonexudative MNV [110]. [PERSON] et al. and [PERSON] et al. found a cumulative incidence of exudation of 24% after 1 year and of 34.5% after 2 years of follow-up in eyes with iAMD [13; 14], whereas [PERSON] et al. described an incidence of exudation of 20% after 15 months of follow up in patients with active neovascular AMD in the contralateral eye [116]. Different results were obtained by [PERSON] et al., who found an incidence of exudation of 80% at 2 years [15]. These differences could be explained by several factors including different populations, the number of patients evaluated, and the duration of AMD. [PERSON] et al. [11] and [PERSON] et al. [110] reported the rate of activation, following the criteria for diagnosis of quiescent CNVs, respectively of 6.6% in patients with iAMD at 1 year of follow-up and of 26.3% in eyes with GA within a mean of 20 months of follow-up.