Apolipoprotein A-I Mimetic Peptide L-4F Removes Bruch's Membrane Lipids in Aged Nonhuman Primates

Discernibility of the Interdigitation Zone (IZ), a Potential Optical Coherence Tomography (OCT) Biomarker for Visual Dysfunction in Aging

PURPOSE

Photoreceptor (PR) outer segments, retinal pigment epithelium apical processes, and inter-PR matrix contribute to the interdigitation zone (IZ) of optical coherence tomography (OCT). We hypothesize that this interface degrades over adulthood, in concert with a delay of rod mediated dark adaptation (RMDA). To explore this idea, we determined IZ discernibility and RMDA in younger and older adults.

METHODS

For this cross-sectional study, eyes of 20 young (20-30 years) and 40 older (≥60 years) participants with normal maculas according to the AREDS 9-step grading system underwent OCT imaging and RMDA testing at 5° superior to the fovea. Custom FIJI plugins enabled analysis for IZ discernibility at 9 eccentricities in 0.5 mm steps on one single horizontal B-scan through the fovea. Locations with discernible IZ met two criteria: visibility on B-scans and a distinct peak on a longitudinal reflectivity profile. The frequency of sites meeting both criteria was compared between both age groups and correlated with rod intercept time (RIT).

RESULTS

The median number of locations with discernible IZ was significantly higher (foveal, 4 vs. 0, p = 0.0099; extra-foveal 6 vs. 0, p < 0.001) in eyes of young (26 ± 3 years) compared to older (73 ± 5 years) participants. For the combined young and older sample, the higher frequency of discernible IZ was correlated with shorter RIT (faster dark adaptation) (rs = -0.56, p < 0.0001). This association was significant within young eyes (rs = -0.54; p = 0.0134) and not within older eyes (rs = -0.29, p = 0.706).

CONCLUSIONS

Results suggest that the interface between outer segments and apical processes degrades in normal aging, potentially contributing to delayed rod-mediated dark adaptation. More research is needed to verify an age-related association between IZ discernibility and rod-mediated dark adaptation. If confirmed in a large sample, IZ discernibility might prove to be a valuable biomarker and predictor for visual function in aging.

Chromatic Pupillometry as a Putative Screening Tool for Heritable Retinal Disease in Rhesus Macaques

Purpose

Non-human primates (NHPs) are useful models for human retinal disease. Chromatic pupillometry has been proposed as a noninvasive method of identifying inherited retinal diseases (IRDs) in humans; however, standard protocols employ time-consuming dark adaptation. We utilized shortened and standard dark-adaptation protocols to compare pupillary light reflex characteristics following chromatic stimulation in rhesus macaques with achromatopsia to wild-type (WT) controls with normal retinal function.

Methods

Nine rhesus macaques homozygous for the p.R656Q mutation (PDE6C HOMs) and nine WT controls were evaluated using chromatic pupillometry following 1-minute versus standard 20-minute dark adaptations. The following outcomes were measured and compared between groups: pupil constriction latency, peak constriction, pupil constriction time, and constriction velocity.

Results

Pupil constriction latency was significantly longer in PDE6C HOMs with red-light (P = 0.0002) and blue-light (P = 0.04) stimulation versus WT controls. Peak constriction was significantly less in PDE6C HOMs with all light stimulation compared to WT controls (P < 0.0001). Pupil constriction time was significantly shorter in PDE6C HOMs versus WT controls with red-light (P = 0.04) and white-light (P = 0.003) stimulation. Pupil constriction velocity was significantly slower in PDE6C HOMs versus WT controls with red-light (P < 0.0001), blue-light (P < 0.0001), and white-light (P = 0.0002) stimulation. Dark adaptation time only significantly affected peak (P = 0.008) and time of pupil constriction (P = 0.02) following blue-light stimulation.

Conclusions

Chromatic pupillometry following 1- and 20-minute dark adaptation is an effective tool for screening NHPs for achromatopsia.

Translational Relevance

Rapid identification of NHPs with IRDs will provide animal research models to advance research and treatment of achromatopia in humans.

Inner retinal degeneration associated with optic nerve head drusen in pseudoxanthoma elasticum

BACKGROUND/AIMS

To determine the association of age, presence of optic nerve head drusen (ONHD) and number of previous intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections with inner retinal layer thicknesses in patients with pseudoxanthoma elasticum (PXE).

METHODS

In this retrospective case-control study, longitudinal spectral-domain optical coherence tomography imaging data from patients with PXE were compared with controls. A custom deep-learning-based segmentation algorithm was trained and validated to quantify the retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL). The association of age, number of anti-VEGF injections and ONHD with the RNFL and GCL thickness in the outer ETDRS subfields as dependent variables was investigated using mixed model regression.

RESULTS

Fourty-eight eyes of 30 patients with PXE were compared with 100 healthy eyes. The mean age was 52.5±12.9 years (range 21.3-68.2) for patients and 54.2±18.7 years (range 18.0-84.5) for controls. In patients, ONHD were visible in 15 eyes from 13 patients and 31 eyes had received anti-VEGF injections. In the multivariable analysis, age (-0.10 µm/year, p<0.001), the diagnosis of PXE (-2.03 µm, p=0.005) and an interaction term between age and the presence of ONHD (-0.20 µm/year, p=0.001) were significantly associated with the GCL thickness. Including the number of intravitreal injections did not improve the model fit. The RNFL thickness was not significantly associated with any of these parameters.

CONCLUSIONS

This study demonstrates a significant association of ageing and ONHD with GCL thinning in patients with PXE, but not with the number of anti-VEGF injections. Given the severity of inner retinal degeneration in PXE, a clinical trial investigating neuroprotective therapy warrants consideration.

Untargeted Lipidomic Profiling of Aged Human Retina With and Without Age-Related Macular Degeneration (AMD)

The molecular characterization of extracellular deposits is crucial to understanding the clinical progression of AMD. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis is a powerful analytical discovery tool capable of identifying lipids in an untargeted manner. NanoLC-MS/MS is an analytical tool capable of identifying lipids with high sensitivity and minimum sample usage. Hence, the purpose of this study was to compare retina lipid identification from RPE-choroid samples using high flow LC-MS/MS and nanoLC-MS/MS. Manually dissected paraformaldehyde-fixed human donor tissues sections were used for LC-MS/MS and nanoLC-MS/MS analysis. Lipids were extracted with MeOH/MTBE/CHCl3 (MMC) and were analyzed by LC-MS/MS and nanoLC-MS/MS using negative and positive ionization modes. Untargeted lipidomics using LC-MS/MS identified 215 lipids from 4 lipid classes and 15 subclasses. We observed a 78% increase in lipid identifications using nanoLC-MS/MS with lipid numbers totaling 384. The nanoLC-MS/MS method is expected to provide extensive lipid identifications from small retina samples, e.g., from drusen and drusenoid deposits in aged and AMD eyes, and could help elucidate how lipids are involved in extracellular deposit formation in AMD.

Visualizing lipid behind the retina in aging and age-related macular degeneration, via indocyanine green angiography (ASHS-LIA)

Age-related macular degeneration (AMD) causes legal blindness in older adults worldwide. Soft drusen are the most extensively documented intraocular risk factor for progression to advanced AMD. A long-standing paradox in AMD pathophysiology has been the vulnerability of Asian populations to polypoidal choroidal vasculopathy (PCV) in the presence of relatively few drusen. Age-related scattered hypofluorescent spots on late phase indocyanine green angiography (ASHS-LIA) was recently proposed as precursors of PCV. Herein, we offer a resolution to the paradox by reviewing evidence that ASHS-LIA indicates the diffuse form of lipoprotein-related lipids accumulating in Bruch's membrane (BrM) throughout adulthood. Deposition of these lipids leads to soft drusen and basal linear deposit (BLinD), a thin layer of soft drusen material in AMD; Pre-BLinD is the precursor. This evidence includes: 1. Both ASHS-LIA and pre-BLinD/BLinD accumulate in older adults and start under the macula; 2. ASHS-LIA shares hypofluorescence with soft drusen, known to be physically continuous with pre-BLinD/BLinD. 3. Model system studies illuminated a mechanism for indocyanine green uptake by retinal pigment epithelium. 4. Neither ASHS-LIA nor pre-BLinD/ BLinD are visible by multimodal imaging anchored on current optical coherence tomography, as confirmed with direct clinicopathologic correlation. To contextualize ASHS-LIA, we also summarize angiographic characteristics of different drusen subtypes in AMD. As possible precursors for PCV, lipid accumulation in forms beyond soft drusen may contribute to the pathogenesis of this prevalent disease in Asia. ASHS-LIA also might help identify patients at risk for progression, of value to clinical trials for therapies targeting early or intermediate AMD.

Ageing fundus degenerations of Macaca fascicularis on multi-modal imaging and histopathology: Similarities and differences compared to human

To characterize the ageing fundus degenerations in Macaca fascicularis, we used multimodal imaging including color fundus photograph, spectral domain optical coherence tomography, fundus autofluorescence, fundus fluorescence angiography, and indocyanine green angiography (ICGA) to survey and track fundus changes of 84 Macaca fascicularis, ranging from 5 to 24 years old over 2 years, and followed by hematoxylin-eosin (HE) and immunofluorescence (IF) staining. The Macaca fascicularis in our cohort showed ageing characteristics different from human, including the more common yellow dot maculopathy, the unique appearance of patchy hyperautoflurescence, and the absence of subretinal drusenoid deposit, basal laminar deposit, geographic atrophy or choroidal neovascularization. Same with human, hard drusen, soft drusen, atherosclerosis, tessellated retina, staining of vessels in peripheral choroid on late-phase ICGA, and peripheral hard drusen were detected. HE and IF staining suggested the patchy hyperautoflurescence to be drusenoid deposits. BMI were significantly higher in the Macaca fascicularis with yellow dot maculopathy and hard drusen, compared to the ones without (p < 0.05). Our study reveals fundus degenerations that develop with ageing in the nonhuman primate of Macaca fascicularis. Their differences and similarities compared to human worth notice by future translational research in degenerative fundus diseases, especially age-related macular degeneration.

Visual Dysfunction and Structural Correlates in Sorsby Fundus Dystrophy

PURPOSE

To elucidate morphological determinants of rod and cone dysfunction in Sorsby fundus dystrophy (SFD), and to systematically compare visual function tests for interventional trials.

DESIGN

Prospective cross-sectional study.

METHODS

Patients with SFD (n = 16) and controls (n = 20) underwent visual function testing (best-corrected visual acuity [BCVA] and low luminance visual acuity [LLVA], contrast sensitivity, mesopic and dark-adapted (DA) fundus-controlled perimetry [FCP], rod-mediated dark adaptation [RMDA]), and multimodal imaging. Vision-related quality of life was evaluated. FCP and RMDA thresholds were analyzed using mixed models and structure-function correlation using machine learning (ML). Longitudinal data of 1 patient with high-dose vitamin A supplementation were available.

RESULTS

Although photopic BCVA was normative in SFD, LLVA was impaired (0.30 LogMAR [0.20; 0.45] vs 0.20 LogMAR [0.03; 0.28], P < .05). Scotopic visual function exhibited a delayed rod-intercept time (21 minutes [12.15; 21] vs 4.05 minutes [3.22; 5.36], P < .001), and marked DA cyan mean sensitivity loss (-11.80 dB [-3.47; -19.85]), paralleled by a reduced vision-related quality of life. ML-based structure-function correlation allowed prediction of mesopic, DA cyan, and red sensitivity with high accuracy (cross-validated mean absolute error: 4.36, 7.77, and 5.31 dB, respectively), whereas RMDA could be slowed even in the absence of fundus alterations on multimodal imaging. After high-dose vitamin A supplementation, RMDA and DA thresholds improved markedly.

CONCLUSIONS

Patients with SFD exhibit severely impaired scotopic visual function even in the absence of funduscopic alterations on multimodal imaging. In contrast to BCVA, scotopic visual function tests are suitable to quantify dysfunction in the early stages. Improvement of scotopic dysfunction after (off-label) high-dose vitamin A intake, as observed in one patient in our study, is compatible with the hypothesized local deficiency of vitamin A secondary to Bruch's membrane alterations.

Peptides as Therapeutic Agents for Atherosclerosis

More than three decades ago, as a test for the amphipathic helix theory, an 18 amino acid residue peptide and its analogs were designed with no sequence homology to any of the exchangeable apolipoproteins. Based on the apolipoprotein A-I (the major protein component of high density lipoproteins, HDL) mimicking properties, they were termed as ApoA-I mimicking peptides. Several laboratories around the world started studying such de novo-designed peptides for their antiatherogenic properties. The present chapter describes the efforts in bringing these peptides as therapeutic agents for atherosclerosis and several lipid-mediated disorders.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

Uncovering of intraspecies macular heterogeneity in cynomolgus monkeys using hybrid machine learning optical coherence tomography image segmentation

The fovea is a depression in the center of the macula and is the site of the highest visual acuity. Optical coherence tomography (OCT) has contributed considerably in elucidating the pathologic changes in the fovea and is now being considered as an accompanying imaging method in drug development, such as antivascular endothelial growth factor and its safety profiling. Because animal numbers are limited in preclinical studies and automatized image evaluation tools have not yet been routinely employed, essential reference data describing the morphologic variations in macular thickness in laboratory cynomolgus monkeys are sparse to nonexistent. A hybrid machine learning algorithm was applied for automated OCT image processing and measurements of central retina thickness and surface area values. Morphological variations and the effects of sex and geographical origin were determined. Based on our findings, the fovea parameters are specific to the geographic origin. Despite morphological similarities among cynomolgus monkeys, considerable variations in the foveolar contour, even within the same species but from different geographic origins, were found. The results of the reference database show that not only the entire retinal thickness, but also the macular subfields, should be considered when designing preclinical studies and in the interpretation of foveal data.

Age-related changes in the rhesus macaque eye

PURPOSE

To assess age-related changes in the rhesus macaque eye and evaluate them to corresponding human age-related eye disease.

METHODS

Data from eye exams and imaging tests including intraocular pressure (IOP), lens thickness, axial length, and retinal optical coherence tomography (OCT) images were evaluated from 142 individuals and statistically analyzed for age-related changes. Quantitative autofluorescence (qAF) was measured as was the presence of macular lesions as related to age.

RESULTS

Ages of the 142 rhesus macaques ranged from 0.7 to 29 years (mean = 16.4 years, stdev = 7.5 years). Anterior segment measurements such as IOP, lens thickness, and axial length were acquired. Advanced retinal imaging in the form of optical coherence tomography and qAF were obtained. Quantitative assessments were made and variations by age groups were analyzed to compare with established age-related changes in human eyes. Quantitative analysis of data revealed age-related increase in intraocular pressure (0.165 mm Hg per increase in year of age), ocular biometry (lens thickness 7.2 μm per increase in year of age; and axial length 52.8 μm per increase in year of age), and presence of macular lesions. Age-related changes in thicknesses of retinal layers on OCT were observed and quantified, showing decreased thickness of the retinal ganglion cell layer and inner nuclear layer, and increased thickness of photoreceptor outer segment and choroidal layers. Age was correlated with increased qAF by 1.021 autofluorescence units per increase in year of age.

CONCLUSIONS

The rhesus macaque has age-related ocular changes similar to humans. IOP increases with age while retinal ganglion cell layer thickness decreases. Macular lesions develop in some aged animals. Our findings support the concept that rhesus macaques may be useful for the study of important age-related diseases such as glaucoma, macular diseases, and cone disorders, and for development of therapies for these diseases.

Visible Light Optical Coherence Tomography (OCT) Quantifies Subcellular Contributions to Outer Retinal Band 4

Purpose

To use visible light optical coherence tomography (OCT) to investigate subcellular reflectivity contributions to the outermost (4th) of the retinal hyperreflective bands visualized by current clinical near-infrared (NIR) OCT.

Methods

Visible light OCT, with 1.0 µm axial resolution, was performed in 28 eyes of 19 human subjects (21–57 years old) without history of ocular pathology. Two foveal and three extrafoveal hyperreflective zones were consistently depicted within band 4 in all eyes. The two outermost hyperreflective bands, occasionally visualized by NIR OCT, were presumed to be the retinal pigment epithelium (RPE) and Bruch's membrane (BM). RPE thickness, BM thickness, and RPE interior reflectivity were quantified topographically across the macula.

Results

A method for correcting RPE multiple scattering tails was found to both improve the Gaussian goodness-of-fit for the BM intensity profile and reduce the coefficient of variation of BM thickness in vivo. No major topographical differences in macular BM thickness were noted. RPE thickness decreased with increasing eccentricity. Visible light OCT signal intensity in the RPE was weighted to the apical side and attenuated more across the RPE in the fovea than peripherally.

Conclusions

Morphometry of the presumed RPE and BM bands is consistent with known anatomy. Weighting of RPE reflectivity toward the apical side suggests that melanosomes are the predominant contributors to RPE backscattering and signal attenuation in young eyes.

Translational Relevance

By enabling morphometric analysis of the RPE and BM, visible light OCT deciphers the main reflectivity contributions to outer retinal band 4, commonly visualized by commercial OCT systems.

ABUNDANCE AND MULTIMODAL VISIBILITY OF SOFT DRUSEN IN EARLY AGE-RELATED MACULAR DEGENERATION: A Clinicopathologic Correlation

PURPOSE

To determine the abundance and multimodal visibility of drusen and basal linear deposit (BLinD) in early age-related macular degeneration.

METHODS

A 69-year-old white man was imaged by color fundus photography and red free photography, fundus autofluorescence, and optical coherence tomography. From en face images, we determined the drusen field, drusen area, and equivalent diameters of individual drusen. From high-resolution light-microscopic histology (6 months after the last clinic visit), we determined the area of drusen, BLinD, and pre-BLinD in a subretinal pigment epithelium-basal lamina lipid field.

RESULTS

In right and left eyes, respectively, BLinD covered 40% and 46% of the lipid field, versus 21% and 14% covered by drusen. The lipid field was covered 60% to 61% by Drusen + BLinD and 65% to 72% by BLinD + pre-BLinD. In the left eye, the drusen area on color fundus photography (0.18 mm) and red free (0.28 mm) was smaller than the drusen area on histology (1.16 mm). Among drusen confirmed by optical coherence tomography, 55.1% and 56.6% were observed on red free and fundus autofluorescence, respectively.

CONCLUSION

Basal linear deposit covered 1.9 and 3.4-fold more fundus area than soft drusen, silently increasing progression risk. Improved visualization of BLinD and readouts of the retinal pigment epithelium health over lipid will assist population surveillance, early detection, and trial outcome measures.

Lipid accumulation and protein modifications of Bruch's membrane in age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive retinal disease, which is the leading cause of blindness in western countries. There is an urgency to establish new therapeutic strategies that could prevent or delay the progression of AMD more efficiently. Until now, the pathogenesis of AMD has remained unclear, limiting the development of the novel therapy. Bruch's membrane (BM) goes through remarkable changes in AMD, playing a significant role during the disease course. The main aim of this review is to present the crucial processes that occur at the level of BM, with special consideration of the lipid accumulation and protein modifications. Besides, some therapies targeted at these molecules and the construction of BM in tissue engineering of retinal pigment epithelium (RPE) cells transplantation were listed. Hopefully, this review may provide a reference for researchers engaged in pathogenesis or management on AMD.

Age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of legal blindness in the industrialized world. AMD is characterized by accumulation of extracellular deposits, namely drusen, along with progressive degeneration of photoreceptors and adjacent tissues. AMD is a multifactorial disease encompassing a complex interplay between ageing, environmental risk factors and genetic susceptibility. Chronic inflammation, lipid deposition, oxidative stress and impaired extracellular matrix maintenance are strongly implicated in AMD pathogenesis. However, the exact interactions of pathophysiological events that culminate in drusen formation and the associated degeneration processes remain to be elucidated. Despite tremendous advances in clinical care and in unravelling pathophysiological mechanisms, the unmet medical need related to AMD remains substantial. Although there have been major breakthroughs in the treatment of exudative AMD, no efficacious treatment is yet available to prevent progressive irreversible photoreceptor degeneration, which leads to central vision loss. Compelling progress in high-resolution retinal imaging has enabled refined phenotyping of AMD in vivo. These insights, in combination with clinicopathological and genetic correlations, have underscored the heterogeneity of AMD. Hence, our current understanding promotes the view that AMD represents a disease spectrum comprising distinct phenotypes with different mechanisms of pathogenesis. Hence, tailoring therapeutics to specific phenotypes and stages may, in the future, be the key to preventing irreversible vision loss.

Pharmacologic activation of autophagy without direct mTOR inhibition as a therapeutic strategy for treating dry macular degeneration

Dry age-related macular degeneration (AMD) is marked by the accumulation of extracellular and intracellular lipid-rich deposits within and around the retinal pigment epithelium (RPE). Inducing autophagy, a conserved, intracellular degradative pathway, is a potential treatment strategy to prevent disease by clearing these deposits. However, mTOR inhibition, the major mechanism for inducing autophagy, disrupts core RPE functions. Here, we screened autophagy inducers that do not directly inhibit mTOR for their potential as an AMD therapeutic in primary human RPE culture. Only two out of more than thirty autophagy inducers tested reliably increased autophagy flux in RPE, emphasizing that autophagy induction mechanistically differs across distinct tissues. In contrast to mTOR inhibitors, these compounds preserved RPE health, and one inducer, the FDA-approved compound flubendazole (FLBZ), reduced the secretion of apolipoprotein that contributes to extracellular deposits termed drusen. Simultaneously, FLBZ increased production of the lipid-degradation product β-hydroxybutyrate, which is used by photoreceptor cells as an energy source. FLBZ also reduced the accumulation of intracellular deposits, termed lipofuscin, and alleviated lipofuscin-induced cellular senescence and tight-junction disruption. FLBZ triggered compaction of lipofuscin-like granules into a potentially less toxic form. Thus, induction of RPE autophagy without direct mTOR inhibition is a promising therapeutic approach for dry AMD.

Biometrics, Impact, and Significance of Basal Linear Deposit and Subretinal Drusenoid Deposit in Age-Related Macular Degeneration

Purpose

Basal linear deposit (BLinD) is a thin layer of soft drusen material. To elucidate the biology of extracellular deposits conferring age-related macular degeneration (AMD) progression risk and inform multimodal clinical imaging based on optical coherence tomography (OCT), we examined lipid content and regional prevalence of BLinD, soft drusen, pre-BLinD, and subretinal drusenoid deposit (SDD) in AMD and non-AMD aged eyes. We estimated BLinD volume and illustrated its relation to type 1 macular neovascularization (MNV).

Methods

Donor eyes were classified as early to intermediate AMD (n = 25) and age-matched controls (n = 54). In high-resolution histology, we assessed BLinD/soft drusen thickness at 836 and 1716 locations in AMD and control eyes, respectively. BLinD volume was estimated using solid geometry in donor eyes, one clinically characterized.

Results

BLinD, drusen, type 1 MNV, and fluid occupy the sub-RPE-basal laminar space. BLinD volume in a 3-mm diameter circle may be as much as 0.0315 mm3. Osmophilic lipid was more concentrated in BLinD/drusen than SDD. In the fovea, BLinD/drusen was prevalent in AMD eyes; pre-BLinD was prevalent in control eyes. SDD was low in the fovea and high in perifovea, especially in AMD eyes.

Conclusions

Although invisible, BLinD may presage type 1 MNV. BLinD volume approaches the criterion OCT drusen volume of 0.03 mm3 for AMD progression risk. BLinD culminates years of subfoveal lipid accumulation. SDD is detected relatively late in life, with currently unknown precursors. Deposit topography suggests one outer retinal lipid recycling system serving specialized cone and rod physiology, and its dysregulation in AMD is due to impaired transfer to the circulation.

Imaging Features Associated with Progression to Geographic Atrophy in Age-Related Macular Degeneration: Classification of Atrophy Meeting Report 5

PURPOSE

To provide an image-based description of retinal features associated with risk for development of geographic atrophy (GA) in eyes with age-related macular degeneration (AMD), as visualized with multimodal imaging anchored by structural OCT.

DESIGN

Consensus meeting.

PARTICIPANTS

International group that included those with expertise in imaging and AMD basic science and histology, and those with Reading Center experience in AMD clinical trials.

METHODS

As part of the Classification of Atrophy Meeting program, an international group of experts analyzed and discussed retinal multimodal imaging features in eyes with AMD associated with GA, risk of progression to GA, or both. Attendees undertook premeeting grading exercises that were reviewed during the meeting sessions. Meeting presentations illustrated established and investigational multimodal imaging features and associated histologic features. Each of these different features were then discussed openly by the entire group to arrive at consensus definitions. These definitions were applied to 40 additional images that were graded independently by attendees to refine the consensus definitions and descriptions further.

RESULTS

Consensus was reached on images with descriptors for 12 features. These features included components of outer retinal atrophy (e.g., ellipsoid zone disruption), components of complete retinal pigment epithelium (RPE) and outer retinal atrophy (e.g., RPE perturbation with associated hypotransmission or hypertransmission), features frequently seen in eyes with atrophy (e.g., refractile drusen), and features conferring risk for atrophy development (e.g., hyperreflective foci, drusen, and subretinal drusenoid deposits).

CONCLUSIONS

An international consensus on terms and descriptions was reached on multimodal imaging features associated GA and with risk for GA progression in eyes with AMD. We believe this information will be useful to clinicians who manage patients with AMD, researchers who study AMD disease interventions and pathogenesis, and those who design clinical trials for therapies targeting earlier AMD stages than GA expansion.

Atlas of Human Retinal Pigment Epithelium Organelles Significant for Clinical Imaging

Purpose

To quantify organelles impacting imaging in the cell body and intact apical processes of human retinal pigment epithelium (RPE), including melanosomes, lipofuscin-melanolipofuscin (LM), mitochondria, and nuclei.

Methods

A normal perifovea of a 21-year-old white male was preserved after rapid organ recovery. An aligned image stack was generated using serial block-face scanning electron microscopy and was annotated by expert readers (TrakEM, ImageJ). Acquired measures included cell body and nuclear volume (n = 17); organelle count in apical processes (n = 17) and cell bodies (n = 8); distance of cell body organelles along a normalized apical-basal axis (n = 8); and dimensions of organelle-bounding boxes in apical processes in selected subsamples of cell bodies and apical processes.

Results

In 2661 sections through 17 cells, apical processes contained 65 ± 24 melanosomes in mononucleate (n = 15) and 131 ± 28 in binucleate cells (n = 2). Cell bodies contained 681 ± 153 LM and 734 ± 170 mitochondria. LM was excluded from the basal quartile, and mitochondria from the apical quartile. Lengths of melanosomes, LM, and mitochondria, respectively were 2305 ± 528, 1320 ± 574, and 1195 ± 294 nm. The ratio of cell body to nucleus volume was 4.6 ± 0.4. LM and mitochondria covered 75% and 63%, respectively, of the retinal imaging plane.

Conclusions

Among RPE signal sources for optical coherence tomography, LM and mitochondria are the most numerous reflective cell body organelles. These and our published data show that most melanosomes are in apical processes. Overlapping LM and previously mitochondria cushions may support multiple reflective bands in cell bodies. This atlas of subcellular reflectivity sources can inform development of advanced optical coherence tomography technologies.

Optimisation of a Novel Bio-Substrate as a Treatment for Atrophic Age-Related Macular Degeneration

Atrophic age-related macular degeneration (AMD) is the most common form of AMD accounting for 90% of patients. During atrophic AMD the waste/exchange pathway between the blood supply (choroid) and the retinal pigment epithelium (RPE) is compromised. This results in atrophy and death of the RPE cells and subsequently the photoreceptors leading to central blindness. Although the mechanisms behind AMD are unknown, the growth of fatty deposits known as drusen, have been shown to play a role in the disease. There is currently no treatment or cure for atrophic AMD. Much research focuses on developing a synthetic substrate in order to transplant healthy cells to the native Bruch’s membrane (BM), however, the diseased native BM and related structures still leave potential for transplanted cells to succumb to disease. In this proof-of-concept work we electrospun poly(ethylene terephthalate) (PET) to fabricate a nanofibrous cytocompatible synthetic BM. The apical surface of the membrane was cultured with ARPE-19 cells and the underside was decorated with poly(lactic acid-co-glycolic acid) (PLGA) or poly(glycolic acid) (PGA) degradable nanoparticles by electrospraying. The membrane exhibited hydrophilicity, high tensile strength and structurally resembled the native BM. ARPE-19 cells were able to form a monolayer on the surface of the membrane and no cell invasion into the membrane was seen. The presence of both PLGA and PGA nanoparticles increased ARPE-19 cell metabolism but had no effect on cell viability. There was a decrease in pH of ARPE-19 cell culture media 7 days following culturing with the PLGA nanoparticles but this change was eliminated by 2 weeks; PGA nanoparticles had no effect on cell culture media pH. The fluorescent dye FITC was encapsulated into nanoparticles and showed sustained release from PLGA nanoparticles for 2 weeks and PGA nanoparticles for 1 day. Future work will focus on encapsulating biologically active moieties to target drusen. This could allow this novel bioactive substrate to be a potential treatment for atrophic AMD that would function two-fold: deliver the required monolayer of healthy RPE cells to the macula on a synthetic BM and remove diseased structures within the retina, restoring the waste/exchange pathway and preventing vision loss.

Hyperreflective Foci and Specks Are Associated with Delayed Rod-Mediated Dark Adaptation in Nonneovascular Age-Related Macular Degeneration

PURPOSE

Hyperreflective foci (HRF) are OCT biomarkers for the progression of nonneovascular age-related macular degeneration (AMD) attributed to anteriorly migrated retinal pigment epithelial cells. We examined associations between rod- and cone-mediated vision and HRF plus smaller hyperreflective specks (HRS); we identified a histologic candidate for HRS.

DESIGN

Cross-sectional study and histologic survey.

PARTICIPANTS

Patients with healthy maculae (n = 34), early AMD (n = 26), and intermediate AMD (n = 41).

METHODS

AMD severity was determined by color fundus photography. In OCT scans, HRF and HRS were counted manually. Vision tests probed cones (best-corrected visual acuity [VA], contrast sensitivity), mixed cones and rods (low-luminance VA, low-luminance deficit, mesopic light sensitivity), or rods (scotopic light sensitivity, rod-mediated dark adaptation [RMDA]). An online AMD histopathologic resource was reviewed.

MAIN OUTCOME MEASURES

Vision in eyes assessed for HRF and HRS; histologic candidate for HRS.

RESULTS

In 101 eyes of 101 patients, HRF and HRS were identified in 25 and 95 eyes, respectively, with good reliability. Hyperreflective foci were present but sparse in healthy eyes, infrequent in early AMD eyes, and frequent but highly variable among intermediate AMD eyes (mean±standard deviation [SD] number per eye, 0.1 ± 0.2, 0.2 ± 0.5, and 1.9 ± 3.4 for healthy, early AMD, and intermediate AMD eyes, respectively). Hyperreflective specks outnumbered HRF in all groups (mean±SD, 4.5 ± 3.2, 6.3 ± 5.8, and 19.4 ± 22.4, respectively). Delayed RMDA was associated strongly with more HRF and HRS (P < 0.0001). Hyperreflective foci also were associated with worse low-luminance VA (P = 0.0117). Hyperreflective specks were associated with worse contrast sensitivity (P = 0.0278), low-luminance VA (P = 0.0010), low-luminance deficit (P = 0.0031), and mesopic (P = 0.0018) and scotopic (P < 0.0001) sensitivity. By histologic analysis, cone lipofuscin was found in outer retinal layers of 25% of healthy aged eyes.

CONCLUSIONS

Hyperreflective foci and HRS are markers of cellular activity associated with visual dysfunction, especially delayed RMDA, an AMD risk indicator assessing efficiency of retinoid resupply. Hyperreflective specks may represent lipofuscin translocating inwardly within cones. HRF and HRS may serve as structural end points in clinical trials targeting AMD stages earlier than atrophy expansion. These results should be confirmed in a larger sample.

Long-term Evolution and Remodeling of Soft Drusen in Rhesus Macaques

Purpose

To characterize the evolution and structure of soft drusen in aged rhesus macaques using in vivo multimodal retinal imaging and ex vivo histologic and ultrastructural analyses as a nonhuman primate model of early age-related macular degeneration (AMD).

Methods

Multimodal imaging including fundus photography, spectral domain optical coherence tomography (SD-OCT), and fundus autofluorescence (FAF) were used to characterize and track individual drusen lesions in 20 aged rhesus macaques (mean age 23.3 ± 2.7 years) with drusenoid lesions over 2 years, followed by semithin histologic analysis and transmission electron microscopy (TEM).

Results

Although most drusen gradually increased in size, a portion spontaneously regressed or collapsed over 2 years. Histologic analyses showed that soft drusen exhibit hypertrophy and dysmorphia of overlying retinal pigment epithelium (RPE), as seen in early and intermediate AMD, but do not exhibit RPE atrophy, RPE migration, or photoreceptor degeneration characteristic of advanced AMD. Ultrastructure of soft drusen showed abundant lipid particles within Bruch's membrane and AMD-related basal linear deposits (BlinD) resembling those in human drusen.

Conclusions

The dynamic remodeling, histologic findings, and ultrastructural features of soft drusen in aged rhesus macaques support nonhuman primates as an animal model of early AMD and reveal important insights into drusen biogenesis and AMD development.

LXRs regulate features of age-related macular degeneration and may be a potential therapeutic target

Effective treatments and animal models for the most prevalent neurodegenerative form of blindness in elderly people, called age-related macular degeneration (AMD), are lacking. Genome-wide association studies have identified lipid metabolism and inflammation as AMD-associated pathogenic pathways. Given liver X receptors (LXRs), encoded by the nuclear receptor subfamily 1 group H members 2 and 3 (NR1H3 and NR1H2), are master regulators of these pathways, herein we investigated the role of LXR in human and mouse eyes as a function of age and disease and tested the therapeutic potential of targeting LXR. We identified immunopositive LXR fragments in human extracellular early dry AMD lesions and a decrease in LXR expression within the retinal pigment epithelium (RPE) as a function of age. Aged mice lacking LXR presented with isoform-dependent ocular pathologies. Specifically, loss of the Nr1h3 isoform resulted in pathobiologies aligned with AMD, supported by compromised visual function, accumulation of native and oxidized lipids in the outer retina, and upregulation of ocular inflammatory cytokines, while absence of Nr1h2 was associated with ocular lipoidal degeneration. LXR activation not only ameliorated lipid accumulation and oxidant-induced injury in RPE cells but also decreased ocular inflammatory markers and lipid deposition in a mouse model, thereby providing translational support for pursuing LXR-active pharmaceuticals as potential therapies for dry AMD.

Evaluating diurnal changes in choroidal sublayer perfusion using optical coherence tomography angiography

PURPOSE

To investigate diurnal changes of choroidal sublayer perfusion in normal eyes and to identify influencing factors using optical coherence tomography angiography (OCTA).

METHODS

A prospective study was conducted on healthy volunteers, each of whom underwent repeated measurements of subfoveal choroidal thickness (SFCT) via enhanced depth imaging (EDI) optical coherence tomography (OCT) as well as perfusion of choroidal vascular sublayers using OCTA at 7 a.m., 12 p.m., 4 p.m. and 8 p.m. Possible interactions between diurnal variations and other factors, such as mean arterial pressure (MAP), gender and age, were evaluated.

RESULTS

A total of 22 eyes from 22 participants were analysed. Mean age of participants was 56 years. A significant pattern of diurnal variation was observed for SFCT (p < 0.001) as well as perfusion of Sattler's layer (SLP; p = 0.009) and Haller's layer (HLP; p = 0.003). SFCT demonstrated a linear decrease, being thicker in the morning (348 μm) and thinner in the evening (310 μm). Both, SLP and HLP showed a quadratic relation to time of day, increasing from morning (64% and 76%) to afternoon (66% and 77%), before decreasing again in the evening (64% and 76%). HLP changes were significantly associated with fluctuations of MAP (B = 0.0007; CI 0.0001-0.0014; p = 0.047). No significant differences with regard to gender were detectable. However, older participants (≥60 years) had fewer diurnal changes (p = 0.042).

CONCLUSION

Optical coherence tomography angiography-based analysis of choroidal sublayer perfusion demonstrated significant diurnal variations. Therefore, it is important to account for time of day, when comparing longitudinal OCTA data.