When evaluating different types of MNV (type 1 and type 2), no differences in FAF parameters were observed. Significant differences were found when comparing active versus inactive MNV. Active MNVs were considered those with subretinal or intraretinal fluid on OCT, which is commonly used in clinical practice to guide treatment decisions, whereas the use of fluorescein angiography has decreased significantly.
16,17,30 The differences included lower mean FAF wavelengths and higher intensities of both green and red emission components in active versus inactive MNV. Especially active MNV with SRF had the highest values in both green and red emission spectra. When we separately evaluated active MNV with SRF versus MNV with IRF, we noticed that MNV with IRF had more signs of chronicity, including fibrosis and outer retina and RPE atrophy on OCT, and a trend to lower BCVA. This negative impact of IRF (cysts) on BCVA versus SRF was also reported in the Comparison of AMD Treatments Trials (CATT) trial, probably due to apoptotic and necrotic cell death, visible on OCT as small intraretinal cysts.
31 Therefore, the values of GEFCs and REFCs were lower than in MNV with SRF with less chronic disease. These quantitative data obtained with color FAF can be considered in line with data obtained with standard blue (488-nm) FAF in neovascular AMD. Whereas an increased pattern of FAF corresponded well with SRF and the edges of the choroidal neovascularization (CNV), indicating a significant accumulation of lipofuscin caused by the compensatory proliferation of RPE cells proximal to CNV when disease progresses,
32 and just in some cases with drusen, a decreased FAF pattern corresponded to fibrovascular/disciform scar, macular atrophy, blood, pigmentary RPE changes, and, in one-third of cases, active MNV.
4,33–36 McBain et al.
6 reported reduced FAF in 90% of eyes with classic CNV (above the RPE, type 2 MNV), whereas in occult CNV (beneath the RPE, type 1 MNV), areas of increased FAF were present, clinically corresponding to SRF. The origin of the increased FAF signal was explained as an increased content in RPE lipofuscin secondary to increased outer segment shedding at sites of chronic neurosensory retinal detachment.
37,38 The decreased FAF (488 nm) documented in classic CNV could not be distinguished from decreased FAF due to macular atrophy, whereas in color FAF, these lesions had very distinct parameters (
Tables 1,
2). Moreover, color FAF allows one to separately detect fluorescence deriving also from minor fluorophores and, with the use of the specific software, to separately quantify the emission intensity in the green and red spectra. In this way, the activity of MNV can be discerned from nonactive MNV, thus supporting a decision on the need for treatment. As quantitative evaluation gives more precise data than qualitative evaluation of color FAF, this method may offer a possibility for automatic evaluation of the images with an indication for treatment. This would need to be confirmed in larger and possibly longitudinal studies.