Optical coherence tomography angiography of types 1 and 2 choroidal neovascularization in age-related macular degeneration during anti-VEGF therapy: evaluation of a new quantitative method

Abstract

The aim of this pilot study was to test whether mathematical parameters of the vascular morphology of choroidal neovascularization (CNV) can be used as biomarkers and to investigate how these parameters change during anti-vascular endothelial growth factor (VEGF) therapy. Methods Treatment-naive CNV in exudative age-related macular degeneration (AMD) was diagnosed in 28 patients. OCTangiography (OCT-A) (Avanti/FA Optovue) performed before and after anti-VEGF therapy. The OCT-A data sets were exported to an external image processing program and vessel skeletonization was accomplished by means of edge detection. Based on this technique the total vessel length, the number of segments and the fractal dimension (FD) of the CNV were calculated before and after therapy. The results were compared with other clinical parameters such as VA and central retinal thickness (RT). Results The total vessel length of the CNV was significantly reduced by anti-VEGF-therapy (mean value 652 pixels vs. 397 pixels; p < 0.0001), as well as the number of individual vessel segments of the CNV (mean value 117 vs. 76; p < 0.0001). The FD of the CNV also decreased significant reduction during therapy (mean 1.23 vs. 1.16, p < 0.0001). The changes in these parameters during treatment corresponded with an increase in VA and a reduction in RT. Conclusion This pilot study demonstrates that the vascular pattern of CNV in AMD can be visualized and described using mathematical parameters of OCT-A. The changes during therapy correlate significantly with established "activity" parameters of CNV, so changes in these parameters (especially FD) may represent additional CNV "activity" biomarkers.

Changes in the OCT angiographic appearance of type 1 and type 2 CNV in exudative AMD during anti-VEGF treatment

“…If further evaluations of OCT-A were to underscore the validity of its characterisation of treatment-relevant CNV morphology, then OCT-A could be used alone for confident diagnosis in the future—certainly a desirable scenario. However, even now CNV can be analysed not only in the active stage, but also in the inactive stage following anti-VEGF treatment 5 13 14. OCT-A also detects ‘silent’ CNV that has led to neither intraretinal nor subretinal fluid and cannot be depicted on SD-OCT or FA 15 16.…”

“…These change under therapy and thus new biomarkers could emerge. In a previous study, we provided a mathematical description of the vascular parameters in type 1 and type 2 CNV and demonstrated significant changes in these parameters following initial anti-VEGF treatment (three injections) 5. We measured the area (aCNV), the total length of all vessels (tlCNV), the overall number of vascular segments (nsCNV) and the fractal dimension (FD) of the CNV.…”

<p>Quantitative Comparison of the Vascular Structure of Macular Neovascularizations Between Swept-Source and Spectral-Domain Optical Coherence Tomography Angiography</p>

“…The flow density (defined as the proportion of all pixels that represent flow) was calculated based on the caliber of the skeletonized MNV. 6,16 Figure 1 shows examples of the various types of MNV in SS-OCTA and SD-OCTA en-face images as well as skeletonized (skeleton computed by a multiscale smoothing approach using the principal components of the structured tensor field 16 ) and binarized (by estimating the vessel calibers: the skeleton lines are adaptively dilated so that the flow pixels are marked by 1 and the non-flow pixels by 0) MNV.…”

“…5 In previous studies, we found significant changes in the vascular structure of MNV and the correlating retinal thickness depending on the disease activity. 6,7 However, only one OCTA device was used for these investigations. Many studies have contrasted the results of devices using different OCTA techniques.…”

Vascular density in age-related macular degeneration after one year of antiVEGF treatment with treat-and-extend and fixed regimens

“…OCT-A has been shown to be a valuable tool in the follow up of CNV, after antiVEGF treatment in patients with nAMD but there are only a few reports on the retinal vascular system of nAMD patients [9]. Faatz et al [23] evaluated the activity of the CNV: measured the total vessel length, the number of segments. They calculated the fractal dimension of the CNV before and after therapy.…”