Retinal Vessel Changes in Geographic Atrophy in AMD: Insights From Imaging and Histology

Abstract

Purpose: The purpose of this study was to investigate retinal vascular changes in geographic atrophy (GA) secondary to age-related macular degeneration (AMD) using swept-source optical coherence tomography angiography (SS-OCTA), and to correlate imaging findings with histology.

Methods: Sixty subjects were enrolled: 20 with GA, 20 with intermediate AMD, and 20 healthy controls. SS-OCTA imaging was used to quantify retinal perfusion density (PD) and vessel length density (VLD) in the superficial capillary plexus (SCP), deep capillary plexus (DCP), and full retina. A topographical analysis distinguished regions with and without retinal pigment epithelium (RPE) atrophy in GA eyes. Additionally, flat-mount immunohistochemistry was performed on a donor eye with GA to assess retinal vasculature. Main outcome measures included PD and VLD across SCP, DCP, and full retina, in regions with and without RPE atrophy.

Results: Retinal PD and VLD were significantly reduced in GA eyes compared with intermediate AMD eyes, particularly in the DCP. Topographical analysis revealed more pronounced vascular impairment in areas with RPE atrophy, whereas regions without RPE atrophy in GA eyes exhibited perfusion comparable to intermediate AMD and healthy controls. Histological analysis confirmed a substantial reduction in vascular density within atrophic regions.

Conclusions: Retinal vascular changes in GA predominantly occur within regions of RPE atrophy. The preservation of perfusion in regions without RPE atrophy suggests that vascular impairment is localized. These findings underscore the importance of regional analysis and histopathologic correlation in understanding vascular remodeling in GA. Future longitudinal OCTA studies are warranted to clarify the temporal progression of these vascular alterations in relation to RPE atrophy.

Figure 1.

Representation of the algorithm used to investigate the retinal perfusion. Images of the full retina, superficial capillary plexus (SCP), and deep capillary plexus (DCP) were imported into ImageJ software (National Institutes of Health; http://imagej.nih.gov/ij/). A thresholding algorithm was applied to generate binarized versions of these images, which were then used to assess perfusion density in the full retina, SCP, and DCP. Perfusion density was calculated as the proportion of white pixels (i.e. those above the threshold) relative to the total number of pixels within the analyzed scan area, and is expressed as a unitless value. To evaluate vessel length density, the binarized images were further processed using skeletonization, producing representations where vessels appear as 1-pixel-wide traces. Vessel length density was defined as the total length of perfused vasculature divided by the total number of pixels in the scan area. The sub-RPE OCT image was used to delineate the area of geographic atrophy, marked by an orange dashed line in the figure. This delineation enabled a topographical analysis comparing regions with and without atrophy.

Figure 2.

Gross photograph and retinal flat-mount image. (A) A gross photograph of the posterior eyecup from a donor with GA, with the retina intact, shows a prominent area of RPE atrophy, appearing whitish compared to the surrounding tissue. (B) A low-magnification image of the retinal flat-mount stained with Ulex europaeus agglutinin 1 (UEA 1) reveals a substantial loss of retinal capillaries within the atrophic region. The green and red staining behind the vasculature defines the subretinal glial membrane (stained with vimentin and VEGF) which mimics the atrophic area in this and other eyes with GA. Nine distinct regions were randomly selected: three within the atrophic area (red boxes), three in a drusen-affected region without signs of atrophy (yellow boxes), and three in an area free of both atrophy and drusen (green boxes). The foveal avascular zone (FAZ) is enlarged compared with the healthy controls.

Figure 3.

Multimodal imaging of a patient with geographic atrophy. (Top row) Fundus photography (left) reveals macular pigmentation changes, including a hypopigmented area where choroidal vessels are more visible due to geographic atrophy, as highlighted in the magnified image (middle). This region appears hypoautofluorescent on green autofluorescence imaging (right). (Second row) The en face image of the superficial capillary plexus (SCP) (left) shows reduced perfusion, particularly in the parafoveal region. The segmentation boundaries used for this analysis are shown on the right. (Third row) The en face image of the deep capillary plexus (DCP) (left) demonstrates a more pronounced reduction in perfusion, especially in the parafoveal region, compared to the SCP. The segmentation boundaries are shown on the right. (Bottom row) To assess retinal perfusion topographically, the en face sub-RPE image (left) highlights areas of hyperTDs corresponding to regions of RPE atrophy. This image was generated using segmentation boundaries positioned at 64 and 400 µm below Bruch’s membrane, as illustrated on the right. All segmentation boundaries were checked and manually adjusted, if necessary, to remove artifacts.

Figure 4.

Multimodal imaging of a patient with intermediate AMD. (Top row) Fundus photography (left) reveals macular pigmentary changes and the presence of large drusen, as highlighted in the magnified view (right). (Middle row) The en face image of the superficial capillary plexus (SCP) (left) shows preserved perfusion. The segmentation boundaries are shown on the right. (Bottom row) The en face image of the deep capillary plexus (DCP) (left) also demonstrates preserved perfusion. The segmentation boundaries are displayed on the right.

Figure 5.

High-magnification UEA 1-stained retinal flat-mount images. High-magnification UEA 1-stained retinal flat-mount images of the nine analyzed regions (see Fig. 2) clearly demonstrate a reduced number of retinal capillaries in the atrophic area (D–F) compared with regions without atrophy or drusen (A–C).