The current study investigated the correlation between alteration in CC perfusion, evaluated using OCT-A, and retinal dysfunction, quantified using MP in patients with iAMD. Overall, we found a reduced PPCA in areas not affected by drusen of iAMD eyes compared to control group. Moreover, among iAMD eyes, more reduced PPCA was associated with worse retinal sensitivity. To date, many studies have been carried out with OCT-A to investigate the role of CC perfusion in the pathogenesis of AMD, which are supported by numerous histopathological hypotheses that explain the reduced CC perfusion and includes: reduced CC flow velocity, reduced number of CC vessels per unit area or decreased CC vessel caliber.
13 All of these possibilities could result in hypoxia of RPE and photoreceptors, with consequent retinal dysfunction. To this regard, several histopathologic studies identified CC disfunction as a relevant factor for the development of AMD.
20–22 In particular, Biesemeier et al.
21 using optical and electron microscopy demonstrated a thickening of the Bruch membrane with the presence of multiple deposits between the RPE and its basement membrane and inside the Bruch membrane itself in eyes with AMD compared to controls. These alterations were associated with increased loss of photoreceptors, RPE cells, and CC. The authors concluded that CC loss is an aging phenomenon that precedes RPE atrophy and photoreceptor loss in AMD.
21 Similarly Seddon et al., in post mortem histopathology studies, demonstrated that CC loss occurs without RPE atrophy in early and iAMD.
23 Furthermore, supporting this hypothesis, by analyzing the EZ band at SD-OCT, which is an anatomic parameter known to be strongly associated with BCVA and visual function, we observed that it was preserved in all patients with iAMD, independently from the number of drusen and from the estimated CC flow. In fact, the EZ band was only rarefied in correspondence to the drusen but always detectable, as evident in the example reported in
Figure 2, which shows a case of AMD in comparison to a healthy subject. Therefore, in addition to evaluation of structural findings by SD-OCT, in particular the EZ band, the measurement of CC perfusion could be sensitive and useful for the early detection of any vascular alterations and for monitoring patients with AMD.