Decreased Macular Choriocapillaris Perfusion in Eyes With Macular Reticular Pseudodrusen Imaged With Swept-Source OCT Angiography

Abstract

Purpose: To determine if macular reticular pseudodrusen (RPD) were associated with markers of impaired macular choroidal perfusion, we investigated measurements of macular choriocapillaris (CC) flow deficits (FDs), CC thickness, and mean choroidal thickness (MCT) in eyes with macular RPD compared with normal eyes and eyes with soft drusen.

Methods: Eyes with intermediate age-related macular degeneration (iAMD) and normal eyes underwent 6 × 6 mm swept-source optical coherence tomography angiography (SS-OCTA) imaging to diagnose macular RPD, occupying over 25% of the fovea-centered 5 mm diameter circle, and measure outer retinal layer (ORL) thickness, CC FDs, CC thickness, MCT, and choroidal vascularity index (CVI) using previously published strategies within the same fovea-centered 5 mm circle.

Results: Ninety eyes were included; 30 normal eyes, 30 eyes with soft drusen, and 30 eyes with macular RPD. The RPD eyes showed higher macular CC FDs than normal eyes (P < 0.001) and soft drusen eyes (P = 0.019). Macular CC thickness was decreased in RPD eyes compared with normal eyes (P < 0.001) and soft drusen eyes (P = 0.016). Macular MCT in RPD eyes was thinner than normal eyes (P = 0.005) and soft drusen eyes (P < 0.001). No statistically and clinically significant differences were found in the ORL thickness and CVI measurements between RPD eyes and the other two groups (all P > 0.05).

Conclusions: Eyes with macular RPD had decreased macular CC perfusion, decreased CC thickness, and decreased MCT measurements compared with normal and soft drusen eyes, suggesting that RPD may result from impaired choroidal perfusion.

Reticular pseudodrusen (RPD), also known as subretinal drusenoid deposits (SDDs), are a feature of age-related macular degeneration (AMD) and other retinal diseases, such as Sorsby fundus dystrophy and pseudoxanthoma elasticum, and they can be found in eyes without any diagnosed retinal disease.^1,2 These deposits, which accumulate above the retinal pigment epithelium (RPE) and under the retina, can be visualized using color fundus (CF) imaging, blue-light fundus reflectance imaging, blue-light autofluorescence (FAF) imaging, infrared reflectance (IR) imaging, and both B-scan and en face optical coherence tomography (OCT) imaging.^1–4 The presence of RPD has been associated with decreased low luminance visual acuity, delayed dark adaptation, poor contrast sensitivity, and decreased photoreceptor sensitivity, as measured by microperimetry.^1,2 Moreover, RPD have been associated with disease progression from intermediate AMD (iAMD) to late-stage AMD, including the formation of type 3 macular neovascularization and the formation and increased growth rates of geographic atrophy.^1,2 In contrast to these previous reports, Wu et al. found that the presence of RPD was not associated with an increased risk of progression from iAMD to late AMD.⁵ 

In AMD, RPD undergo a dynamic redistribution over time with the most common initial topographic location involving the region superior to the macula followed by the subsequent spread to the nasal, temporal, inferior, and macular regions as the superiorly distributed RPD regress.^1,2 The disappearance and redistribution of RPD are often associated with the predominant loss of rod photoreceptors and outer retinal thinning in the regions previously occupied by RPD.^1,2 Previous reports have explored the association between the presence of RPD and choroidal perfusion abnormalities by colocalizing RPD with choroidal filling defects detected using fluorescein and indocyanine green angiography.^6–8 More indirect measurements of choroidal perfusion have included macular choroidal thickness and choroidal vascularity index (CVI) measurements.^1,2 Even though most RPD are outside the central macula, the presence of RPD has been associated with decreased macular choroidal thickness and CVI measurements compared with controls.^1,2,9–11 However, in reporting the association between RPD and increased macular choriocapillaris (CC) perfusion deficits imaged with optical coherence tomography angiography (OCTA), four published reports have associated CC perfusion impairment with the presence of RPD,^6,12–14 whereas two reports failed to show an association between RPD and CC perfusion deficits.^15,16 

There are several difficulties when comparing published reports describing the associations between RPD and various aspects of macular physiology and visual function in AMD, but the most obvious issue is that there is no reproducible method for quantifying the extent of RPD, and this is particularly true over time because RPD have a dynamic redistribution and will change as AMD progresses.^1,2,16 For example, the definition of RPD was determined by both confocal scanning ophthalmoscopy and spectral-domain OCT (SD-OCT) in the report by Alten et al.,⁶ by both near-infrared (NIR) images and SD-OCT scans in the report by Clemons et al.,¹⁴ and by FAF and IR imaging by Nesper et al.¹² The study by Chatziralli et al.¹³ relied on retinal specialists to establish the diagnosis of RPD based on indirect ophthalmoscopy, IR imaging, and SD-OCT imaging. Of note, there was no minimum threshold to establish the diagnosis of RPD in the above studies. However, in the reports by Nam et al.¹⁵ and Wu et al.,¹⁶ a minimum number of RPD were required. In the report by Nam et al.,¹⁵ RPD were diagnosed if at least 10 hyper-reflective triangular-shaped lesions above the RPE were present on both a 6 × 6 mm fovea-centered OCT macula scan and on macular CF imaging. Meanwhile, Wu et al.¹⁶ also proposed a minimum number of RPD to establish the diagnosis of RPD with the diagnosis requiring 5 or more definite RPD present on more than one OCT B-scan from a 6 × 6mm fovea-centered raster scan, as well as RPD being definitely present or questionably present on at least one or more en face imaging modalities, which included CF, NIR, and FAF imaging, or RPD had to be definitely present on two or more the en face imaging modalities. It is interesting to note that in both reports that required a minimum number of lesions for the diagnosis, neither of them showed an association between macular CC perfusion abnormalities and RPD. One of the underlying assumptions from all the previous studies investigating the relationship between RPD and abnormalities in CC perfusion was that the presence of RPD within the imaging field-of-view (FOV) should be adequate to establish the association between RPD and CC perfusion abnormalities, even though the CC perfusion was not necessarily measured where the RPD were located. However, as previously shown from studies using the early treatment diabetic retinopathy study (ETDRS) grid superimposed on the macula,^6,14 there only appeared to be an association between RPD and CC perfusion abnormalities when they were co-localized within the grid. If the presence of RPD does correspond to underlying CC abnormalities, then it stands to reason that the area with the highest density of RPD should correspond to the area with the most compromised CC perfusion, as we recently reported in a patient with Sorsby macular dystrophy.¹⁷ One strategy to test this relationship would be to measure CC perfusion abnormalities outside the central macula where most RPD predominate, but this presents technical challenges using current OCT instruments. Another strategy would be to select patients with an abundance of RPD within the region of a typical fovea-centered macular scan. 

In this report, we identified eyes with an abundance of RPD in the central macula of eyes with iAMD and compared these eyes to age-controlled normal eyes and eyes with typical soft drusen without any RPD to determine if RPD were associated with markers of decreased macular choroidal perfusion. 

Methods

This prospective OCT imaging study was approved by the Institutional Review Board of University of Miami Miller School of Medicine. The study was performed in accordance with the tenets of the Declaration of Helsinki and complied with the Health Insurance Portability and Accountability Act of 1996. Written informed consents were obtained from all participants before enrollment. 

A retrospective review of subjects enrolled from April 2016 to August 2022 identified 3 groups of eyes: normal eyes without any ocular disease, iAMD eyes with typical soft drusen only, and iAMD eyes with RPD. The presence of RPD was detected using the SS-OCT structural en face images of a 20 µm thick slab which was 20 µm to 40 µm above the RPE layer, as previously described.^3,4,17 The regions of RPD within the scans were outlined by two graders (authors J.L. and M.S.), and agreement between graders was reached. No attempt was made to grade the different phenotypes of RPD. The percentage of the RPD area within a fovea-centered 5 mm circle was then assessed, and eyes having at least 25% area of the fovea-centered 5 mm circle occupied by RPD were included and referred to as having macular RPD. Exclusion criteria for enrollment included confounding ocular conditions such as an axial length ≤23 mm or ≥26 mm, glaucoma, and chorioretinal disorders other than soft drusen or RPD. After inclusion of the RPD group, the age-matched normal group and the soft drusen group were identified from the prospective study cohort. Normal subjects were healthy volunteers with no visual complaints, a normal ocular history, and no identified optic disc, retinal, or choroidal pathology on examination.^18,19 Eyes with soft drusen secondary to iAMD had no other confounding ocular conditions. 

Image Acquisition

All eyes underwent SS-OCT imaging (PLEX Elite 9000, Carl Zeiss Meditec, Inc., Dublin, CA, USA). The SS-OCT instrument has a laser light source with a central wavelength of 1050 nm, a bandwidth of 100 nm, and an axial resolution in tissue of approximately 5 µm with a transverse resolution at the retinal surface of approximately 20 µm. The instrument operated at a scanning speed of 100,000 A-scans per second. All patients were imaged using the SS-OCT angiography (SS-OCTA) 6 × 6 mm scan pattern centered on the fovea. This scan pattern consisted of 500 A-scans per B-scan. The angiographic flow information was obtained using the complex optical microangiographic algorithm known as OMAG^C that generated the flow signals from the variations in both the OCT signal magnitude and phase information between sequential B-scans acquired at the same position.^20,21 

Some eyes also underwent additional imaging of the macula that included CF imaging with a 50-degree FOV centered on the fovea (TRC-50DX; Topcon Medical Systems, Japan), FAF imaging with a 30 degrees FOV centered on the fovea (HRA-II, Spectralis; Heidelberg Engineering, Germany), and NIR imaging with a 30 degrees FOV centered on the fovea (HRA-II, Spectralis; Heidelberg Engineering, Germany). 

Image Processing

The drusen volume measurements were generated using a validated algorithm known as the Advanced RPE Analysis Algorithm version 0.10, which was available on the Advanced Retinal Imaging Network website (Carl Zeiss Meditec, USA).²² The outer retinal layer (ORL) thickness was measured using an algorithm that segmented the inner boundary of the outer plexiform layer OPL to the RPE layer as previously described.²³ Visualization and quantitation of the CC flow deficits (FDs) were obtained using a 16 µm thick slab that started 4 µm beneath the Bruch's membrane (BM).²⁴ En face images of the retinal and CC were produced and were used to compensate for any signal loss due to the overlying anatomy when generating en face CC flow images.^25–27 The measurements of CC FDs were obtained from the compensated CC flow images after excluding areas with hyperpigmentation. Global thresholding was performed by applying the fuzzy C-means method (FCM method), as previously described to produce the binary CC FD maps for the final CC quantification.^28,29 The percentage of CC FDs (CC FD%) was defined as the ratio of FD area to the total quantifiable area within a given region. The CC thickness measurement was obtained using a peak detection algorithm as previously described.³⁰ The choroidal layer was segmented using a previously published algorithm that detected the distance from BM to the choroidal-scleral interface.⁹ Otsu's global threshold method was applied to identify choroidal vessels from the choroidal slab,¹⁰ and the CVI was calculated as the ratio of the choroidal vessel volume to the total choroidal volume within a given region.⁹ The mean choroidal thickness (MCT) was calculated as the mean value of the choroidal thickness measurements over a defined region. All measurements were performed within a 5 mm circle centered on the fovea. 

Statistical Analysis

Statistical analyses were performed with IBM Statistical Package for the Social Sciences (SPSS) software version 28 (IBM, USA) with a P value of <0.05 considered to be statistically significant. Continuous data were described as mean ± standard deviation. Independent sample t-test compared the means of two groups. Analysis of variance (ANOVA) analyzed the differences among the three groups. 

Results

Ninety eyes were included in this retrospective review from our prospective SS-OCT study. Among them, 30 eyes (30 patients) were normal controls, 30 eyes (25 patients) were diagnosed with soft drusen, and 30 eyes (23 patients) had macular RPD that on average occupied 70.84% of the fovea-centered 5 mm circle (range = 25.17% to 100%). The 3 groups were age matched (ANOVA P > 0.05), with the mean age being 72.87 ± 8.68 years in the normal group, 72.37 ± 6.18 years in the soft drusen group, and 73.57 ± 8.20 years in the RPD group. The mean drusen volume within the fovea-centered 5 mm circle was 0.12 ± 0.07 mm³ in the soft drusen group and 0.01 ± 0.02 mm³ in the RPD group. Figure 1 shows multimodal imaging of two eyes with macular RPD. Figure 2 shows representative examples of a normal eye, an eye with soft drusen, and an eye with macular RPD along with corresponding images and measurements of drusen volume, CC FDs (CC FD%), and CC thickness maps. 

Figure 1.

 

Representative examples of multimodal imaging of macular reticular pseudodrusen in eyes with intermediate age-related macular degeneration. (A-F) Right eye of a 74-year-old man. (G-L) Left eye of the same man. A and G Color fundus images showing yellow drusen deposits in the macula consistent with reticular pseudodrusen (RPD). B and H Fundus autofluorescence images showing macular hyporeflective dots consistent with RPD. C and I Infrared reflectance image showing multiple irregular dots consistent with RPD. D and J SS-OCT en face structural images of a 20 µm thick slab located 20 µm above the retinal pigment epithelium (RPE) showing irregular dots in the macula consistent with RPD. Yellow circles indicate 5 mm diameter circles centered on the fovea. The area with RPD in the fovea-centered 5 mm circles was 100% D and 93% J. The horizontal blue lines indicate the position of the corresponding B-scans in E, F, K, and L. E and K SS-OCT B-scans with the segmentation line used to image RPD and F and L the same B-scans without the segmentation lines showing subretinal drusenoid deposits above the RPE consistent with RPD.

Figure 2.

 

En face images showing maps depicting drusen volume, choriocapillaris flow deficits, and CC thickness measurements in representative examples of a normal eye, an eye with soft drusen, and an eye with macular reticular pseudodrusen. Representative examples of a normal eye (A-E), a soft drusen eye (F-J), and an eye with macular reticular pseudodrusen (RPD) (K-O, same eye with RPD shown in Figs. 1G-L). The color bars beneath columns 1 and 5 correspond to the color-coded measurements of drusen volume and CC thickness, respectively. A, F, and K Drusen elevation maps generated from the SS-OCT Advanced RPE Analysis Algorithm version 0.10. The maps were shown in color with a dynamic range of 0 to 100 µm. The white 5 mm circle centered on the fovea indicates the areas that were used to measure the drusen volume (A = 0 mm³, F = 0.07 mm³, and K = 0.00 mm³) respectively. B, G, and L En face structural images from the CC slab. C, H, and M Compensated choriocapillaris (CC) flow images. D, I, and N Binary CC flow deficit (FD) images used to measure the percentages of CC FDs (CC FD%; white foci denote the CC FDs). The white 5 mm circle centered on the fovea indicates the area was used to measure the CC FDs. The results were 7.97% D, 8.78% I, and 13.46% N, respectively. E, J, and O CC thickness maps shown in color with a dynamic range of 0 to 40 µm. The black 5 mm circle centered on the fovea indicates the area that were used to measure the thickness. The CC thickness measurements were 12.08 µm E, 9.95 µm J, and 7.14 µm O, respectively.

The accompanying Table shows the comparison of SS-OCT mean characteristics among the three groups. There were no statistically significant differences in the ORL thickness measurements (all P > 0.05). When comparing the CC FD% between the groups (Fig. 3A), normal controls had fewer CC FDs than the soft drusen group (P < 0.001) and the RPD group (P < 0.001). The soft drusen group had fewer CC FDs than the RPD group (P = 0.019). There were also significant differences in CC thickness measurements among the groups (Fig. 3B). The normal group had greater CC thickness than the soft drusen group (P = 0.010), and the RPD group had less CC thickness than both the normal group (P < 0.001) and the soft drusen group (P = 0.016). 

Figure 3.

 

Choriocapillaris flow deficit percentages and CC thickness measurements within the fovea-centered 5 mm circle in the normal group, soft drusen group, and the reticular pseudodrusen group. (A) Percentage of choriocapillaris flow deficits (CC FD%) from the normal, soft drusen, and reticular pseudodrusen (RPD) groups within the fovea-centered 5 mm circles. The CC FD% was lowest in the normal group (8.02% ± 0.88%) and highest in the RPD group (10.67% ± 1.96%). (B) CC thickness measurements in the 5 mm circle was highest in the normal group (9.29 ± 1.22 µm) and thinnest in the RPD group (7.32 ± 1.61 µm).

A comparison of the MCT measurements (see the Table) showed no significant difference between the normal and soft drusen groups (P = 0.436), but the MCT measurement was the thinnest in the RPD group and statistically significant differences were found when compared with normal eyes (P = 0.005) and soft drusen eyes (P < 0.001). A comparison between the CVI measurements (see the Table) showed a marginal difference between the normal and soft drusen group (0.59 ± 0.03 vs. 0.61 ± 0.04, P = 0.027), with the difference being 0.02 and not considered to be clinically significant. No statistically significant differences in CVI were found between the normal group and the RPD group or between the soft drusen group and RPD group (both P > 0.05). 

Table.

 

Mean SS-OCT Measurements Within Fovea-Centered 5 mm Circles From the Normal, Soft Drusen, and Reticular Pseudodrusen Groups.

 

Discussion

We used published and validated SS-OCTA algorithms to study the ORL thickness, CC FD%, CC thickness, MCT, and CVI in eyes with macular RPD, eyes with only soft drusen, and normal eyes. When comparing these eyes, we found a statistically significant increase in macular CC FDs, a decrease in CC thickness, and a decrease in MCT in eyes with macular RPD. Unlike previous studies that either qualitatively assessed for the presence of RPD or specified a minimum number of RPD as 5 or 10 in their imaging FOV, we investigated eyes in which RPD occupied at least 25% of the 5 mm fovea-centered circle, and then we correlated our choroidal measurements with the presence of the macular RPD.^15,16 It was reassuring to find that the decrease in CC perfusion corresponded with a thinning of CC thickness measurements and a thinning of the MCT measurements within the same 5 mm circle. Unlike previous reports that did not necessarily measure choroidal parameters in the areas that were colocalized with the RPD, we focused on choroidal measurements in the same 5 mm circular region where at least 25% of area were occupied by RPD. This strategy reflects our hypothesis that RPD arise in response to localized choroidal perfusion abnormalities and do not necessarily reflect fundus-wide perfusion abnormalities. In addition, it seems likely that more than just a few RPD need to be present before a quantitative association between RPD and the underlying choroidal changes can be established. This might explain the variable results reported in the literature.^1,2,15,16 If most RPD appear outside the central macula, which is not the region that is usually scanned using OCT imaging, and if RPD arise in response to local choroidal perfusion abnormalities, then it should not be surprising if previous reports failed to detect macular choroidal perfusion changes associated with RPD.^15,16 Although there might be global choroidal perfusion abnormalities once RPD meet a certain threshold, we specifically chose eyes with macular RPD to definitively establish an association between macular RPD and macular choroidal abnormalities. 

Our results are consistent with the hypothesis that reduced choroidal perfusion is responsible for the presence of RPD, but a cause-and-effect relationship is by no means established. It is possible that RPD arise as an independent manifestation of AMD or some other retinal disease, and their presence is independent of impaired choroidal and CC perfusion. There may be a mechanism whereby the presence of RPD, which may arise in response to a dysfunctional RPE-photoreceptor complex, causes decreased CC perfusion, increased CC thinning, and decreased choroidal thickness, but such a mechanism has yet to be elucidated. Although it is possible that diseased RPE might cause both the formation of RPD and CC perfusion abnormalities, the importance of a healthy RPE for the maintenance of the CC was called into a question by our recent report looking at the CC in the bed of RPE tears in eyes with AMD.³¹ We found that even after the removal of the RPE due to the formation of the tear, the CC persisted for over a year, which suggested that the presence of the CC was not dependent on an intact RPE, although the CC may not possess the typical fenestrations. Therefore, if the absence of the RPE does not impact the SS-OCTA detection of the CC, then it is difficult to envision how a diseased RPE with RPD would impact the CC and choroid in the short term. Of note, even though we did not study the function of photoreceptors in our study, there were no significant ORL thickness changes above RPD, but this should not be surprising because outer retinal atrophy has been shown to develop as RPD regress.^1,2 

We propose that RPD form in response to localized perfusion abnormalities in the choroid that are exacerbated by perfusion abnormalities that arise upstream to the ocular circulation, perhaps as a result of ophthalmic artery or carotid artery perfusion defects due to underlying atherosclerotic and cardiovascular disease.^32–36 This proposed mechanism of RPD formation assumes that decreased ocular perfusion in eyes that are genetically at-risk for AMD results in the formation of RPD and the location of the RPD depend upon the variability of the choroidal circulation. This proposed mechanism would also account for the presence of RPD in normal eyes that do not have the typical genetic manifestations of AMD but may be exposed to decreased choroidal perfusion. 

Our study is the most comprehensive to date in terms of SS-OCT measurements in RPD eyes. The main limitation of our study was the relatively small sample size. Another limitation is that we did not grade the different phenotypes of RPD. However, despite these limitations, we did observe significantly decreased macular choroidal perfusion under macular RPD, and a larger sample size would only enhance the statistical significance shown in our study and it is unlikely that this association would change based on the phenotypes of RPD. In addition, although we did take ocular risk factors and age into account when comparing the choroidal perfusion among the groups, we did not include a consideration of systemic risk factors, such as hypertension and cardiovascular diseases because that information was not available for our subjects with normal eyes. Another limitation is that our eyes with macular RPD had at least 25% RPD in the central macula, and we did not have enough of a RPD distribution to make a definitive statement about the minimum percentage needed to see the choroidal associations. Although it is possible that our selection of AMD eyes with an abundance of macular RPD may not represent the typical RPD eyes and may correspond to the phenotype of AMD that more rapidly progresses to macular atrophy,¹ the association between macular RPD and increased localized CC FDs remains robust. 

In summary, we found statistically significant associations between the presence of RPD in the macula and measurements of decreased choroidal perfusion within the macular region where the RPD predominate. Although regions outside the macula were not studied, we propose that our observations within the macula might be extrapolated to these extramacular regions, and our results are consistent with a disease model in which RPD arise in response to decreased choroidal perfusion where the RPD are located. 

Acknowledgments

The authors appreciate the help of Linda O'Koren and Mark Lazcano, Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, in obtaining the SS-OCTA scans. 

Supported by grants from the Salah Foundation, National Eye Institute (R01EY028753), Carl Zeiss Meditec, Inc., Dublin, CA, an unrestricted grant from the Research to Prevent Blindness, Inc., New York, NY, and the National Eye Institute Center Core Grant (P30EY014801) to the Department of Ophthalmology, University of Miami Miller School of Medicine. The funding organizations had no role in the design or conduct of this research. 

Disclosure: J. Li, None; Z. Liu, None; J. Lu, None; M. Shen, None; Y. Cheng, None; N. Siddiqui, None; H. Zhou, None; Q. Zhang, Carl Zeiss Meditec (E); J. Liu, None; G. Herrera, None; F.E. Hiya, None; G. Gregori, Carl Zeiss Meditec (P, R), University of Miami (P); R.K. Wang, Carl Zeiss Meditec (C), Insight Photonic Solutions (C), Colgate Palmolive (R), Estee Lauder Inc. (R), Oregon Health and Science University (I), University of Washington (I); P.J. Rosenfeld, Alexion (R), Annexon (C), Apellis (C, F), Bayer (C), Boehringer-Ingelheim (C), Carl Zeiss Meditec (C, R), Chengdu Kanghong Biotech (C), Gyroscope Therapeutics (R), InflammX Therapeutics (C), Ocudyne (C, F), Regeneron (C), Stealth Bio Therapeutics (R), Unity Biotechnology (C), Valitor (F), Verana Health (F)