OCT-angiography for assessing risk of retinal pigment epithelium tear in patients with vascular retinal pigment epithelium detachment due to AMD.

Abstract

Tears of the retinal pigment epithelium (RPE) usually cause a deleterious loss in visual acuity and are most commonly associated with previous vascularized retinal pigment epithelium detachment (vPED) due to age-related macular degeneration (AMD) (Pauleikhoff et al. 2002). Recent studies suggest an increase in RPE tear incidences since the introduction of anti-vascular endothelial growth factor (VEGF) therapies. Therefore, clinicians increasingly direct the focus on the challenge of RPE tear prevention. Several prognostic markers for an impending RPE tear have been described such as vPED lesion's height, hyper-reflective lines in near-infrared images, subretinal clefts, microrips and duration of vPED (Clemens & Eter 2016). Chan and co-workers (2007) firstly described the morphologic proportions of choroidal neovascularization (CNV) and PED lesion as particularly relevant for the likelihood of tear development. A small ratio of CNV size to PED size turned out to correlate with a higher rate of RPE tears. This concept of CNV/PED ratio was based on fluorescence angiographic (FA) data. We report the applicability of the CNV/PED ratio to optical coherence tomography angiography (OCT-A) imaging. Two patients underwent spectral-domain optical coherence tomography and FA imaging as well as OCT-A examinations (Fig. 1). The first patient showed a serous-vascularized PED due to AMD. Fluorescence angiography (FA) shows a shading background fluorescence in the area of the PED in the early phase, followed by an irregular hyperfluorescence at the margin of the PED corresponding to the CNV, which results in a CNV/PED ratio of approximately 0.2 (Fig. 1A). Correspondingly, OCT-A reveals a distinct flow signal within a neovascular network underneath the PED lesion. The entire network is contained in the detached area resulting in a comparable ratio of 0.3 (Fig. 1C). In the second patient, FA imaging revealed a fibrovascular PED with underlying occult CNV and a CNV/PED ratio of approximately 0.7 (Fig. 1B). Corresponding OCT-A shows a neovascular network almost entirely filling out the PED lesion resulting in a CNV/PED ratio of 0.8 (Fig. 1D). OCT-A imaging produces three-dimensional data. Therefore, measurements of vPED lesions can be performed in different retinal layers. Accordingly, vPED and CNV dimensions may vary in OCT-A. Two-dimensional FA images usually visualize the largest lesion diameter. Accordingly, OCT-A measurements were performed in the layer in which vPED and CNV dimensions showed their maximum diameters. Notably, projection artefacts from retinal vessels may influence the visualization of sub-RPE CNV in OCT-A imaging, which must be taken into consideration when determining CNV dimensions (Spaide et al. 2015). OCT-A imaging may be a useful adjunct to the conventional method of FA for CNV/PED ratio assessment as OCT-A visualizes the actual CNV dimensions, whereas CNV measurement in FA is significantly confounded by dye leakage and usually remains an estimate. A critical issue in OCT-A imaging of CNVs under PED represents the slab thickness. A thin slab may not include the maximal dimensions of the CNV membrane resulting in a false CNV/PED ratio, while a thick slab is prone to produce image artefacts. In conclusion, OCT-A allows for a non-invasive assessment of the CNV/PED ratio in vPED patients that represents an important predictive factor of RPE tear development at the beginning as well as in the course of an anti-VEGF treatment. A future study including a higher number of patients must evaluate in how far dimensions of CNV membrane under the PED agree between FA and OCT-A, which will be crucial regarding the relevance as well as the clinical interpretation of the CNV/PED ratio assessed by OCT-A as a risk factor for impending RPE tear development.