Subretinal Glial Membranes in Eyes With Geographic Atrophy

A Hydrogel-Based Multiplex Coculture Platform for Retinal Component Cells

There is growing interest in generating in vitro models of tissues and tissue-related diseases to mimic normal tissue organization and pathogenesis for different purposes. The retina is a highly complex multicellular tissue where the organization of the cellular components relative to each other is critical for retinal function. Many retinopathies arise due to the disruption of this order. In this study, we aimed to generate a coculture model of retina-derived cells, namely RPE and Müller cells, in multiplexed 3D hydrogels. Using methacrylated gelatin (GelMA)-based 3D hydrogels, we compared the behavior of RPE and Müller cells when they were cultured together. These patterned multiplex hydrogels containing cells were cultured for several days to reflect how cells would reorganize themselves in the presence of another cellular component derived from the same tissue. Here, we present a multicellular multiplex platform for the creation of cellular networks with cells of retinal tissue that can be easily adapted to create more complex tissue-like alternatives for large-scale tissue modeling and screening purposes. We also present an alternative method of coculture by generating spheroids from one of the components while keeping the other component free and motile in the hydrogel. The latter model predicts enhanced possibilities of cellular interactions by retarding the movement of one of the component cells.

Müller cells trophism and pathology as the next therapeutic targets for retinal diseases

Müller cells are a crucial retinal cell type involved in multiple regulatory processes and functions that are essential for retinal health and functionality. Acting as structural and functional support for retinal neurons and photoreceptors, Müller cells produce growth factors, regulate ion and fluid homeostasis, and facilitate neuronal signaling. They play a pivotal role in retinal morphogenesis and cell differentiation, significantly contributing to macular development. Due to their radial morphology and unique cytoskeletal organization, Müller cells act as optical fibers, efficiently channeling photons directly to the photoreceptors. In response to retinal damage, Müller cells undergo specific gene expression and functional changes that serve as a first line of defense for neurons, but can also lead to unwarranted cell dysfunction, contributing to cell death and neurodegeneration. In some species, Müller cells can reactivate their developmental program, promoting retinal regeneration and plasticity-a remarkable ability that holds promising therapeutic potential if harnessed in mammals. The crucial and multifaceted roles of Müller cells-that we propose to collectively call "Müller cells trophism"-highlight the necessity of maintaining their functionality. Dysfunction of Müller cells, termed "Müller cells pathology," has been associated with a plethora of retinal diseases, including age-related macular degeneration, diabetic retinopathy, vitreomacular disorders, macular telangiectasia, and inherited retinal dystrophies. In this review, we outline how even subtle disruptions in Müller cells trophism can drive the pathological cascade of Müller cells pathology, emphasizing the need for targeted therapies to preserve retinal health and prevent disease progression.

MSC exosomes and MSC exosomes loaded with LncRNA H19 as nanotherapeutics regulate the neurogenetic potential of Müller Glial Cells in dry age-related macular degeneration

In retinal degeneration diseases such as dry age-related macular degeneration (AMD), Müller Glial Cells (MGCs) in mammals undergo a process of reactive gliosis leading to the progression of dry AMD. Here, It is demonstrated that exosomes derived from mesenchymal stem cells (MSC exosomes) and MSC exosomes loaded with LncRNA H19, acting as nanotherapeutics, can be regulated by MGCs in dry AMD. In the in vivo study, MSC exosomes were administered via intravitreal injection. MSC exosomes effectively redirected MGCs from gliosis to dedifferentiation and alleviated MGCs-to-epithelial transition by inhibiting oxidative stress in mice with dry AMD induced by NaIO3. In the in vitro study, MSC exosomes promoted MGCs dedifferentiation by activating Wnt/β-catenin signaling pathway and prevented oxidative stress-induced MGCs gliosis and MGCs-to-epithelial transition by inhibiting TGFβ1 signaling pathway. MSC exosomes loaded with LncRNA H19 enhanced the activation of Wnt/β-catenin signaling pathway and the inhibition of the TGFβ1 signaling pathway compared with MSC exosomes. These results suggest that MSC exosomes regulate the neurogenetic potential of MGCs by redirecting MGCs from gliosis to dedifferentiation and alleviating the transformation of MGCs to epithelial cells through regulating oxidative stress. Regulating LncRNA H19 in MGCs to promote mammalian retinal regeneration in dry AMD was suggested for the first time.

Dicer Loss in Müller Glia Leads to a Defined Sequence of Pathological Events Beginning With Cone Dysfunction

Purpose

The loss of Dicer in Müller glia (MG) results in severe photoreceptor degeneration, as it occurs in retinitis pigmentosa or age-related macular degeneration; however, the sequence of events leading to this severe degenerative state is unknown. The aim of this study was to conduct a chronological functional and structural characterization of the pathological events in MG-specific Dicer-conditional knockout (cKO) mice in vivo and histologically.

Methods

To delete Dicer and mature microRNAs (miRNAs) in MG, two conditional Dicer1 knockout mouse strains (Rlbp-CreER:tdTomato:Dicer-cKOMG and Glast-CreER:tdTomato:Dicer-cKOMG) were created. Optical coherence tomography (OCT), electroretinograms (ERGs), and histological analyses were conducted to investigate structural and functional changes up to 6 months after Dicer deletion.

Results

Dicer/miRNA loss in MG leads to (1) impairments of the area spanning from the external limiting membrane (ELM) to the retinal pigment epithelium (RPE), (2) cone photoreceptor dysfunction, and (3) retinal remodeling and functional loss of the inner retina at 1, 3, and 6 months after Dicer loss, respectively, in both of the knockout mouse strains. Furthermore, in the Rlbp-CreER:tdTomato:Dicer-cKOMG strain, rod photoreceptor impairment was found 4 months after Dicer depletion (4) accompanied by alteration of RPE integrity (5).

Conclusions

MG Dicer loss in the adult mouse retina impacts cone function prior to any measurable changes in rod function, suggesting a pivotal role for MG Dicer and miRNAs in supporting cone health. A partially impaired RPE, however, seems to accelerate rod degeneration and overall degenerative events.

Immunohistochemistry and Spatial Density of Müller Cells in the Human Fovea

Purpose

Previous evidence indicates that molecular properties of foveal Müller cells are different from those in the peripheral retina. Here we aimed to characterize Müller cells in the human fovea (including the foveal floor) with specific focus on their spatial density and immunohistochemistry.

Methods

Human retinas were obtained postmortem from male and female donors with no known eye disease (aged 31-56 years) or after exenteration (one 75-year-old patient with no retinal disease and one 86-year-old patient with reticular pseudodrusen). Vertical sections through the macula were processed for immunofluorescence using antibodies against cellular retinaldehyde binding protein (CRALBP), glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), transient receptor potential vanilloid 4 (TRPV4), excitatory amino acid transporter 4 (EAAT4), calbindin, and RNA-binding protein with multiple splicing. Sections were imaged using high-resolution, multichannel confocal microscopy.

Results

Immunofluorescence for CRALBP and GS was found in Müller cells, including their processes throughout the retina. GFAP expression was found in astrocytes outside the fovea and in some foveal somas. Müller cell nuclei had a peak density of about 35,000 cells/mm2 at 500 µm eccentricity. Calbindin was coexpressed with CRALBP in up to 96% of Müller cells in the fovea, but at eccentricities beyond about 1.5 mm calbindin was not expressed by Müller cells. Conversely, calbindin expression in cone photoreceptors was absent in foveal but present in peripheral retina.

Conclusions

This study supports the hypothesis that Müller cells in the macula have distinct structural, functional, and immunohistochemical properties compared to their peripheral counterparts.

Regional Alterations in Müller Cell Protein Expression in Human and a Rat Model of Geographic Atrophy

Purpose

Despite being crucial to neuronal survival, the role Müller cells play in geographic atrophy (GA) has only recently been considered. We investigated whether Müller cells retain their normal functional profile or form a fibrotic scar when remodeling in human GA eyes and our subretinal sodium iodate (NaIO3) model.

Methods

Sprague Dawley rats given subretinal injections of NaIO3 (5 mg/mL) were sacrificed at 3 and 12 weeks. Cryosections and retinal flatmounts from rats and cryosections from human GA eyes were stained with antibodies against the Müller cell proteins glutamine synthetase (GS), inwardly rectifying potassium channel 4.1 (Kir4.1), aquaporin 4 (AQP4), cellular retinaldehyde-binding protein 1 (CRALBP), and glial fibrillary acidic protein (GFAP), as well as alpha smooth muscle actin (α-SMA), fibronectin, and collagens I and IV. The immunofluorescence intensity of AQP4 and Kir4.1 was quantified using Image J, and Kir4.1 protein levels were verified by western blot.

Results

In both human GA eyes and NaIO3-injected rats, Müller cell processes at the external limiting membrane (ELM) descent and in the subretinal membrane exhibited increased GS expression. GFAP was elevated throughout the Müller cells. AQP4 staining at the ELM descent was particularly pronounced throughout the radial processes, including those extending into the subretinal space. In NaIO3-injected rats, perivascular Kir4.1 expression significantly decreased in the atrophic retina, but expression increased in the subretinal glial membrane. α-SMA and extracellular matrix proteins were not detected in the subretinal membrane.

Conclusions

Our findings underscore the persistence of homeostatic proteins, albeit altered, in Müller cells as they remodel and extend into the subretinal space.

Hyperautofluorescent material inside areas of macular atrophy may reveal non-lipofuscin fluorophores in late stage AMD

PURPOSE

To characterize fundus autofluorescence (FAF) in complete (cRORA) and incomplete retinal pigment epithelium and outer retinal atrophy (iRORA) by fluorescence lifetime imaging ophthalmology (FLIO).

METHODS

Overall, 98 macular atrophy (MA) lesions in 42 eyes of 37 age-related macular degeneration (AMD) patients (mean age: 80.9 ± 5.8 years), 25 of them classified as iRORA and 73 as cRORA by OCT, were investigated by FLIO in a short (SSC: 498-560 nm) and a long wavelength channel (LSC: 560-720 nm). Differences of FAF lifetimes and peak emission wavelength (PEW) between atrophic lesions and intact retinal pigment epithelium (RPE) in the outer ring of the ETDRS grid were considered.

RESULTS

FAF lifetimes in MA were longer and PEW were significantly (p < 0.001) shorter than in intact RPE by 112 ± 78 ps (SSC), 91 ± 64 ps (LSC), 27 ± 18 nm (PEW) in iRORA and by 227 ± 112 ps (SSC), 167 ± 81 ps (LSC), and 54 ± 17 nm (PEW) in cRORA. 37% of iRORA and 24% of cRORA were hyperautofluorescent in SSC. Persistent sub-RPE-BL material in MA was newly found as a hyperautofluorescent entity with lifetimes considerably longer than that of drusen and RPE.

CONCLUSIONS

Despite RPE and, thus, lipofuscin are greatly absent in MA, considerable FAF, preferably at short wavelengths, was found in those lesions. Drusen, persistent sub-RPE-BL material, basal laminar deposits, persistent activated RPE, and sclera were identified as putative sources of this fluorescence. FLIO can help to characterize respective fluorophores.

Dicer loss in Müller glia leads to a defined sequence of pathological events beginning with cone dysfunction

Purpose

The loss of Dicer in Müller glia (MG) results in severe photoreceptor degeneration as it occurs in retinitis pigmentosa or AMD. However, the sequence of events leading to this severe degenerative state is unknown. The aim of this study was to conduct a chronological functional and structural characterization of the pathological events in MG-specific Dicer-cKO mice in vivo and histologically.

Methods

To delete Dicer and mature microRNAs (miRNAs) in MG, two conditional Dicer1 knock-out mouse strains namely RlbpCre:Dicer-cKO MG and GlastCre:Dicer-cKO MG, were created. Optical coherence tomography (OCT), electroretinograms (ERGs) as well as histological analyses were conducted to investigate structural and functional changes up to six months after Dicer deletion.

Results

Dicer/miRNA loss in MG leads to 1) impairments of the external limiting membrane (ELM) - retinal pigment epithelium (RPE), 2) cone photoreceptor dysfunction and 3) retinal remodeling and functional loss of the inner retina, 1, 3 and 6 months after Dicer loss, respectively, in both strains. Furthermore, in the Rlbp:Dicer-cKO MG strain, rod photoreceptor impairment was found 4 months after Dicer depletion (4) accompanied by alteration of RPE integrity (5).

Conclusions

MG Dicer loss in the adult mouse retina impacts cone function prior to any measurable changes in rod function, suggesting a pivotal role for MG Dicer and miRNAs in supporting cone health. A partially impaired RPE however seems to accelerate rod degeneration and overall degenerative events.

Fundus Autofluorescence Variation in Geographic Atrophy of Age-Related Macular Degeneration: A Clinicopathologic Correlation

Purpose

The purpose of this study was to develop ground-truth histology about contributors to variable fundus autofluorescence (FAF) signal and thus inform patient selection for treating geographic atrophy (GA) in age-related macular degeneration (AMD).

Methods

One woman with bilateral multifocal GA, foveal sparing, and thick choroids underwent 535 to 580 nm excitation FAF in 6 clinic visits (11 to 6 years before death). The left eye was preserved 5 hours after death. Eye-tracked ex vivo imaging aligned sub-micrometer epoxy resin sections (n = 140, 60 µm apart) with clinic data. Light microscopic morphology corresponding to FAF features assessed included drusen-driven atrophy, persistent hyperautofluorescence (hyperFAF) islands and peninsulas within atrophy, and hyperFAF and hypoautofluorescence (hypoFAF) inner junctional zone (IJZ) and outer junctional zone (OJZ) relative to descent of external limiting membrane (ELM). Atrophy growth rate was calculated.

Results

HypoFAF atrophic spots appeared in association with drusen, and then expanded and coalesced. Over drusen (n = 45, all calcified), RPE was continuous and thin, photoreceptors were short or absent, and initially intact ELM descended where RPE was absent. In persistent hyperFAF within atrophy and in the OJZ, the RPE was continuous and dysmorphic, photoreceptors were present and short, and BLamD was thick. In the IJZ, mottled FAF corresponded to dissociated RPE atop persistent BLamD. Overall linear growth rate (0.198 mm/ year) typified multifocal GA.

Conclusions

FAF in GA is locally multifactorial, with photoreceptor shortening potentially promoting hyperFAF by increasing incoming excitation light available to RPE fluorophores. RPE dysmorphia may lead to either longer or shorter pathlength for excitation light. At both atrophy initiation and expansion Müller glia are major participants.

Systemic Sodium Iodate Injection as a Model for Expanding Geographic Atrophy

Purpose

Geographic atrophy (GA), an advanced form of dry age-related macular degeneration (AMD), has limited treatment options. This study introduces a novel mouse model featuring an expanding GA patch that can be used to test mechanisms and therapeutics.

Methods

C57Bl/6J male mice (n = 96) aged 9-10 weeks received an intraperitoneal (IP) injection of 20 mg/kg sodium iodate (NaIO3). In vivo confocal scanning laser ophthalmoscope (cSLO) and optical coherence tomography imaging were done at one, four, eight, and 16 weeks after injection, with GA area measurements taken at weeks 8 and 16. Mice were euthanized on weeks 8 and 16 for histological analysis.

Results

Administration of 20 mg/kg intraperitoneal NaIO3 caused variable damage levels. Approximately 22% of cases showed damage (speckled autofluorescence) covering 35% to 90% of the 102° field of view cSLO image at one week after injection. These mice developed an expanding patch of GA by week 8, with a mean 1.45-fold increase in area by week 16. This region showed complete photoreceptor and retinal pigment epithelium loss and complement activation at the atrophy edge, whereas the inner retina remained undamaged. Mice with less damage (48% of cases) only developed incomplete outer retinal degeneration, and mice with more damage (30% of cases) had too much GA for measurable expansion.

Conclusions

Although expanding GA formed in only 22% of mice, the model's simplicity and predictability for GA development via one-week post-injection imaging make it suitable for GA therapeutic experimentation.

Translational Relevance

This murine model provides a valuable tool for testing GA therapies, mirroring clinical endpoints relevant to human trials.

The mechanics of the retina: Müller glia role on retinal extracellular matrix and modelling

The retina is a highly heterogeneous tissue, both cell-wise but also regarding its extracellular matrix (ECM). The stiffness of the ECM is pivotal in retinal development and maturation and has also been associated with the onset and/or progression of numerous retinal pathologies, such as glaucoma, proliferative vitreoretinopathy (PVR), age-related macular degeneration (AMD), epiretinal membrane (ERM) formation or uveitis. Nonetheless, much remains unknown about the biomechanical milieu of the retina, and specifically the role that Müller glia play as principal mechanosensors and major producers of ECM constituents. So far, new approaches need to be developed to further the knowledge in the field of retinal mechanobiology for ECM-target applications to arise. In this review, we focus on the involvement of Müller glia in shaping and altering the retinal ECM under both physiological and pathological conditions and look into various biomaterial options to more accurately replicate the impact of matrix stiffness in vitro.

Histologic and Immunohistochemical Characterization of GA-Like Pathology in the Rat Subretinal Sodium Iodate Model

Purpose

Geographic atrophy (GA) is an advanced form of dry age-related macular degeneration with multifactorial etiology and no well-established treatment. A model recapitulating the hallmarks would serve as a key to understanding the underlying pathologic mechanisms better. In this report, we further characterized our previously reported subretinal sodium iodate model of GA.

Methods

Retinal degeneration was induced in rats (6-8 weeks old) by subretinal injections of NaIO3 as described previously. Animals were sacrificed at 3, 8 and 12 weeks after injection and eyes were fixed or cryopreserved. Some choroids were processed as flatmounts while other eyes were cryopreserved, sectioned, and immunolabeled with a panel of antibodies. Finally, some eyes were prepared for transmission electron microscopic (TEM) analysis.

Results

NaIO3 subretinal injection resulted in a well-defined focal area of retinal pigment epithelium (RPE) degeneration surrounded by viable RPE. These atrophic lesions expanded over time. RPE morphologic changes at the border consisted of hypertrophy, multilayering, and the possible development of a migrating phenotype. Immunostaining of retinal sections demonstrated external limiting membrane descent, outer retinal tubulation (ORT), and extension of Müller cells toward RPE forming a glial membrane in the subretinal space of the atrophic area. TEM findings demonstrated RPE autophagy, cellular constituents of ORT, glial membranes, basal laminar deposits, and defects in Bruch's membrane.

Conclusions

In this study, we showed pathologic features of a rodent model resembling human GA in a temporal order through histology, immunofluorescence, and TEM analysis and gained insights into the cellular and subcellular levels of the GA-like phenotypes.

Translational Relevance

Despite its acute nature, the expansion of atrophy and the GA-like border in this rat model makes it ideal for studying disease progression and provides a treatment window to test potential therapeutics for GA.

Müller Glial Cells in the Macula: Their Activation and Cell-Cell Interactions in Age-Related Macular Degeneration

Müller glia, the main glial cell of the retina, are critical for neuronal and vascular homeostasis in the retina. During age-related macular degeneration (AMD) pathogenesis, Müller glial activation, remodeling, and migrations are reported in the areas of retinal pigment epithelial (RPE) degeneration, photoreceptor loss, and choroidal neovascularization (CNV) lesions. Despite this evidence indicating glial activation localized to the regions of AMD pathogenesis, it is unclear whether these glial responses contribute to AMD pathology or occur merely as a bystander effect. In this review, we summarize how Müller glia are affected in AMD retinas and share a prospect on how Müller glial stress might directly contribute to the pathogenesis of AMD. The goal of this review is to highlight the need for future studies investigating the Müller cell's role in AMD. This may lead to a better understanding of AMD pathology, including the conversion from dry to wet AMD, which has no effective therapy currently and may shed light on drug intolerance and resistance to current treatments.

Clearance phagocytosis by the retinal pigment epithelial during photoreceptor outer segment renewal: Molecular mechanisms and relation to retinal inflammation

Mammalian photoreceptor outer segment renewal is a highly coordinated process that hinges on timed cell signaling between photoreceptor neurons and the adjacent retinal pigment epithelial (RPE). It is a strictly rhythmic, synchronized process that underlies in part circadian regulation. We highlight findings from recently developed methods that quantify distinct phases of outer segment renewal in retinal tissue. At light onset, outer segments expose the conserved "eat-me" signal phosphatidylserine exclusively at their distal, most aged tip. A coordinated two-receptor efferocytosis process follows, in which ligands bridge outer segment phosphatidylserine with the RPE receptors αvβ5 integrin, inducing cytosolic signaling toward Rac1 and focal adhesion kinase/MERTK, and with MERTK directly, additionally inhibiting RhoA/ROCK and thus enabling F-actin dynamics favoring outer segment fragment engulfment. Photoreceptors and RPE persist for life with each RPE cell in the eye servicing dozens of overlying photoreceptors. Thus, RPE cells phagocytose more often and process more material than any other cell type. Mutant mice with impaired outer segment renewal largely retain functional photoreceptors and retinal integrity. However, when anti-inflammatory signaling in the RPE via MERTK or the related TYRO3 is lacking, catastrophic inflammation leads to immune cell infiltration that swiftly destroys the retina causing blindness.

Contribution of common and rare variants to Asian neovascular age-related macular degeneration subtypes

Neovascular age-related macular degeneration (nAMD), along with its clinical subtype known as polypoidal choroidal vasculopathy (PCV), are among the leading causes of vision loss in elderly Asians. In a genome-wide association study (GWAS) comprising 3,128 nAMD (1,555 PCV and 1,573 typical nAMD), and 5,493 controls of East Asian ancestry, we identify twelve loci, of which four are novel ([Formula: see text]). Substantial genetic sharing between PCV and typical nAMD is noted (rg = 0.666), whereas collagen extracellular matrix and fibrosis-related pathways are more pronounced for PCV. Whole-exome sequencing in 259 PCV patients revealed functional rare variants burden in collagen type I alpha 1 chain gene (COL1A1; [Formula: see text]) and potential enrichment of functional rare mutations at AMD-associated loci. At the GATA binding protein 5 (GATA5) locus, the most significant GWAS novel loci, the expressions of genes including laminin subunit alpha 5 (Lama5), mitochondrial ribosome associated GTPase 2 (Mtg2), and collagen type IX alpha 3 chain (Col9A3), are significantly induced during retinal angiogenesis and subretinal fibrosis in murine models. Furthermore, retinoic acid increased the expression of LAMA5 and MTG2 in vitro. Taken together, our data provide insights into the genetic basis of AMD pathogenesis in the Asian population.

Subretinal Pseudocysts: A Comprehensive Analysis of this Novel OCT Finding

INTRODUCTION

In current clinical practice, several optical coherence tomography (OCT) biomarkers have been proposed for the assessment of severity and prognosis of different retinal diseases. Subretinal pseudocysts are subretinal cystoid spaces with hyperreflective borders and only a few single cases have been reported thus far. The aim of the study was to characterize and investigate this novel OCT finding, exploring its clinical outcome.

METHODS

Patients were evaluated retrospectively across different centers. The inclusion criterion was the presence of subretinal cystoid space on OCT scans, regardless of concurrent retinal diseases. Baseline examination was set as the first time the subretinal pseudocyst was identified by OCT. Medical and ophthalmological histories were collected at baseline. OCT and OCT-angiography were performed at baseline and at each follow-up examination.

RESULTS

Twenty-eight eyes were included in the study and 31 subretinal pseudocysts were characterized. Out of 28 eyes, 16 were diagnosed with neovascular age-related macular degeneration (AMD), 7 with central serous chorioretinopathy, 4 with diabetic retinopathy, and 1 with angioid streaks. Subretinal and intraretinal fluid were present in 25 and 13 eyes, respectively. Mean distance of the subretinal pseudocyst from the fovea was 686 µm. The diameter of the pseudocyst was positively associated with the height of the subretinal fluid (r = 0.46; p = 0.018) and central macular thickness (r = 0.612; p = 0.001). At follow-up, subretinal pseudocysts disappeared in most of the reimaged eyes (16 out of 17). Of these, two patients presented retinal atrophy at baseline examination and eight patients (47%) developed retinal atrophy at follow-up. Conversely, seven eyes (41%) did not develop retinal atrophy.

CONCLUSION

Subretinal pseudocysts are precarious OCT findings, usually disclosed in a context of subretinal fluid, and are probably transient alterations within the photoreceptor outer segments and retinal pigment epithelium (RPE) layer. Despite their nature, subretinal pseudocysts have been associated with photoreceptor loss and incomplete RPE definition.

Biologically Guided Optimization of Test Target Location for Rod-mediated Dark Adaptation in Age-related Macular Degeneration: Alabama Study on Early Age-related Macular Degeneration 2 Baseline

Purpose

We evaluate the impact of test target location in assessing rod-mediated dark adaptation (RMDA) along the transition from normal aging to intermediate age-related macular degeneration (AMD). We consider whether RMDA slows because the test locations are near mechanisms leading to or resulting from high-risk extracellular deposits. Soft drusen cluster under the fovea and extend to the inner ring of the ETDRS grid where rods are sparse. Subretinal drusenoid deposits (SDDs) appear first in the outer superior subfield of the ETDRS grid where rod photoreceptors are maximal and spread toward the fovea without covering it.

Design

Cross-sectional.

Participants

Adults ≥ 60 years with normal older maculas, early AMD, or intermediate AMD as defined by the Age-Related Eye Disease Study (AREDS) 9-step and Beckman grading systems.

Methods

In 1 eye per participant, RMDA was assessed at 5° and at 12° in the superior retina. Subretinal drusenoid deposit presence was identified with multi-modal imaging.

Main Outcome Measures

Rod intercept time (RIT) as a measure of RMDA rate at 5° and 12°.

Results

In 438 eyes of 438 persons, RIT was significantly longer (i.e., RMDA is slower) at 5° than at 12° for each AMD severity group. Differences among groups were bigger at 5° than at 12°. At 5°, SDD presence was associated with longer RIT as compared to SDD absence at early and intermediate AMD but not in normal eyes. At 12°, SDD presence was associated with longer RIT in intermediate AMD only, and not in normal or early AMD eyes. Findings were similar in eyes stratified by AREDS 9-step and Beckman systems.

Conclusions

We probed RMDA in relation to current models of deposit-driven AMD progression organized around photoreceptor topography. In eyes with SDD, slowed RMDA occurs at 5° where these deposits typically do not appear until later in AMD. Even in eyes lacking detectable SDD, RMDA at 5° is slower than at 12°. The effect at 5° may be attributed to mechanisms associated with the accumulation of soft drusen and precursors under the macula lutea throughout adulthood. These data will facilitate the design of efficient clinical trials for interventions that aim to delay AMD progression.

Ex Vivo OCT-Based Multimodal Imaging of Human Donor Eyes for Research into Age-Related Macular Degeneration

A progression sequence for age-related macular degeneration (AMD) learned from optical coherence tomography (OCT)-based multimodal (MMI) clinical imaging could add prognostic value to laboratory findings. In this work, ex vivo OCT and MMI were applied to human donor eyes prior to retinal tissue sectioning. The eyes were recovered from non-diabetic white donors aged ≥80 years old, with a death-to-preservation time (DtoP) of ≤6 h. The globes were recovered on-site, scored with an 18 mm trephine to facilitate cornea removal, and immersed in buffered 4% paraformaldehyde. Color fundus images were acquired after anterior segment removal with a dissecting scope and an SLR camera using trans-, epi-, and flash illumination at three magnifications. The globes were placed in a buffer within a custom-designed chamber with a 60 diopter lens. They were imaged with spectral domain OCT (30° macula cube, 30 µm spacing, averaging = 25), near-infrared reflectance, 488 nm autofluorescence, and 787 nm autofluorescence. The AMD eyes showed a change in the retinal pigment epithelium (RPE), with drusen or subretinal drusenoid deposits (SDDs), with or without neovascularization, and without evidence of other causes. Between June 2016 and September 2017, 94 right eyes and 90 left eyes were recovered (DtoP: 3.9 ± 1.0 h). Of the 184 eyes, 40.2% had AMD, including early intermediate (22.8%), atrophic (7.6%), and neovascular (9.8%) AMD, and 39.7% had unremarkable maculas. Drusen, SDDs, hyper-reflective foci, atrophy, and fibrovascular scars were identified using OCT. Artifacts included tissue opacification, detachments (bacillary, retinal, RPE, choroidal), foveal cystic change, an undulating RPE, and mechanical damage. To guide the cryo-sectioning, OCT volumes were used to find the fovea and optic nerve head landmarks and specific pathologies. The ex vivo volumes were registered with the in vivo volumes by selecting the reference function for eye tracking. The ex vivo visibility of the pathology seen in vivo depends on the preservation quality. Within 16 months, 75 rapid DtoP donor eyes at all stages of AMD were recovered and staged using clinical MMI methods.

Clinicopathologic Findings in Three Siblings With Geographic Atrophy

Purpose

Age-related macular degeneration (AMD) is a leading cause of blindness among the elderly worldwide. Clinical imaging and histopathologic studies are crucial to understanding disease pathology. This study combined clinical observations of three brothers with geographic atrophy (GA), followed for 20 years, with histopathologic analysis.

Methods

For two of the three brothers, clinical images were taken in 2016, 2 years prior to death. Immunohistochemistry, on both flat-mounts and cross sections, histology, and transmission electron microscopy were used to compare the choroid and retina in GA eyes to those of age-matched controls.

Results

Ulex europaeus agglutinin (UEA) lectin staining of the choroid demonstrated a significant reduction in the percent vascular area and vessel diameter. In one donor, histopathologic analysis demonstrated two separate areas with choroidal neovascularization (CNV). Reevaluation of swept-source optical coherence tomography angiography (SS-OCTA) images revealed CNV in two of the brothers. UEA lectin also revealed a significant reduction in retinal vasculature in the atrophic area. A subretinal glial membrane, composed of processes positive for glial fibrillary acidic protein and/or vimentin, occupied areas identical to those of retinal pigment epithelium (RPE) and choroidal atrophy in all three AMD donors. SS-OCTA also demonstrated presumed calcific drusen in the two donors imaged in 2016. Immunohistochemical analysis and alizarin red S staining verified calcium within drusen, which was ensheathed by glial processes.

Conclusions

This study demonstrates the importance of clinicohistopathologic correlation studies. It emphasizes the need to better understand how the symbiotic relationship between choriocapillaris and RPE, glial response, and calcified drusen impact GA progression.

Modeling inducible neuropathologies of the retina with differential phenotypes in organoids

Neurodegenerative diseases remain incompletely understood and therapies are needed. Stem cell-derived organoid models facilitate fundamental and translational medicine research. However, to which extent differential neuronal and glial pathologic processes can be reproduced in current systems is still unclear. Here, we tested 16 different chemical, physical, and cell functional manipulations in mouse retina organoids to further explore this. Some of the treatments induce differential phenotypes, indicating that organoids are competent to reproduce distinct pathologic processes. Notably, mouse retina organoids even reproduce a complex pathology phenotype with combined photoreceptor neurodegeneration and glial pathologies upon combined (not single) application of HBEGF and TNF, two factors previously associated with neurodegenerative diseases. Pharmacological inhibitors for MAPK signaling completely prevent photoreceptor and glial pathologies, while inhibitors for Rho/ROCK, NFkB, and CDK4 differentially affect them. In conclusion, mouse retina organoids facilitate reproduction of distinct and complex pathologies, mechanistic access, insights for further organoid optimization, and modeling of differential phenotypes for future applications in fundamental and translational medicine research.

HBEGF-TNF induce a complex outer retinal pathology with photoreceptor cell extrusion in human organoids

Human organoids could facilitate research of complex and currently incurable neuropathologies, such as age-related macular degeneration (AMD) which causes blindness. Here, we establish a human retinal organoid system reproducing several parameters of the human retina, including some within the macula, to model a complex combination of photoreceptor and glial pathologies. We show that combined application of TNF and HBEGF, factors associated with neuropathologies, is sufficient to induce photoreceptor degeneration, glial pathologies, dyslamination, and scar formation: These develop simultaneously and progressively as one complex phenotype. Histologic, transcriptome, live-imaging, and mechanistic studies reveal a previously unknown pathomechanism: Photoreceptor neurodegeneration via cell extrusion. This could be relevant for aging, AMD, and some inherited diseases. Pharmacological inhibitors of the mechanosensor PIEZO1, MAPK, and actomyosin each avert pathogenesis; a PIEZO1 activator induces photoreceptor extrusion. Our model offers mechanistic insights, hypotheses for neuropathologies, and it could be used to develop therapies to prevent vision loss or to regenerate the retina in patients suffering from AMD and other diseases.

Glial remodeling and choroidal vascular pathology in eyes from two donors with Choroideremia

Choroideremia (CHM) is a recessive, X-linked disease that affects 1 in 50,000 people worldwide. CHM causes night blindness in teenage years with vision loss progressing over the next two to three decades. While CHM is known to cause progressive loss of retinal pigment epithelial (RPE) cells, photoreceptors and choroidal vessels, little attention has been given to retinal glial changes in eyes with CHM. In addition, while choroidal loss has been observed clinically, no histopathologic assessment of choroidal loss has been done. We investigated glial remodeling and activation as well as choriocapillaris changes and their association with RPE loss in postmortem eyes from two donors with CHM. Eyes were fixed and cryopreserved or the retina and choroid/RPE were processed as flatmounts with a small piece cut for transmission electron microscopy. A dense glial membrane, made up of vimentin and GFAP double-positive cells, occupied the subretinal space in the area of RPE and photoreceptor loss of both eyes. The membranes did not extend into the far periphery, where RPE and photoreceptors were viable. A glial membrane was also found on the vitreoretinal surface. Transmission electron microscopy analysis demonstrated prominence and disorganization of glial cells, which contained exosome-like vesicles. UEA lectin demonstrated complete absence of choriocapillaris in areas with RPE loss while some large choroidal vessels remained viable. In the far periphery, where the RPE monolayer was intact, choriocapillaris appeared normal. The extensive glial remodeling present in eyes with CHM should be taken into account when therapies such as stem cell replacement are considered as it could impede cells entering the retina. This gliosis would also need to be reversed to some extent for Müller cells to perform their normal homeostatic functions in the retina. Future studies investigating donor eyes as well as clinical imaging from carriers or those with earlier stages of CHM will prove valuable in understanding the glial changes, which could affect disease progression if they occur early. This would also provide insights into the progression of disease in the photoreceptor/RPE/choriocapillaris complex, which is crucial for identifying new treatments and finding the windows for treatment.

SUBRETINAL TRANSIENT HYPOREFLECTIVITY IN AGE-RELATED MACULAR DEGENERATION: A Spectral Domain Optical Coherence Tomography Study

PURPOSE

To describe and assess the prognostic significance of subretinal transient hyporeflectivity (STHR) on a novel spectral domain optical coherence tomography (SD-OCT) in age-related macular degeneration.

METHODS

Consecutive patients with age-related macular degeneration (AMD) presenting STHR, defined as a small, well-defined, round subretinal, hyporeflective lesion, on SD-OCT and without exudative signs were included. Clinical examination and SD-OCT (SPECTRALIS, Heidelberg Engineering, Heidelberg, Germany) were analyzed at inclusion, 1 month before inclusion, and until the onset of exudative signs during the 12-month follow-up.

RESULTS

Thirty-five STHR in 21 eyes of 20 patients were included. Among the 21 eyes, 2 eyes had early AMD, 1 eye had nonexudative asymptomatic macular neovascularization, and 18 eyes presented late AMD: 17 eyes neovascular AMD and 1 eye geographic atrophy. During the 2-month follow-up, 97.1% (34/35) of STHR disappeared. During the 12-month follow-up, 57.1% of eyes (12/21) developed exudative signs on 1 eye with early AMD and 11 eyes with neovascular AMD.

CONCLUSION

Subretinal transient hyporeflectivity is a novel SD-OCT sign in patients with AMD. The eyes with isolated STHR should be closely monitored on a monthly basis to detect further exudation.

Localized Structural and Functional Deficits in a Nonhuman Primate Model of Outer Retinal Atrophy

Purpose

Cell-based therapy development for geographic atrophy (GA) in age-related macular degeneration (AMD) is hampered by the paucity of models of localized photoreceptor and retinal pigment epithelium (RPE) degeneration. We aimed to characterize the structural and functional deficits in a laser-induced nonhuman primate model, including an analysis of the choroid.

Methods

Macular laser photocoagulation was applied in four macaques. Fundus photography, optical coherence tomography (OCT), dye angiography, and OCT-angiography were conducted over 4.5 months, with histological correlation. Longitudinal changes in spatially resolved macular dysfunction were measured using multifocal electroretinography (MFERG).

Results

Lesion features, depending on laser settings, included photoreceptor layer degeneration, inner retinal sparing, skip lesions, RPE elevation, and neovascularization. The intralesional choroid was degenerated. The normalized mean MFERG amplitude within lesions was consistently lower than control regions (0.94 ± 0.35 vs. 1.10 ± 0.27, P = 0.032 at month 1, 0.67 ± 0.22 vs. 0.83 ± 0.15, P = 0.0002 at month 2, and 0.97 ± 0.31 vs. 1.20 ± 0.21, P < 0.0001 at month 3.5). The intertest variation of mean MFERG amplitudes in rings 1 to 5 ranged from 13.0% to 26.0% in normal eyes.

Conclusions

Laser application in this model caused localized outer retinal, RPE, and choriocapillaris loss. Localized dysfunction was apparent by MFERG in the first month after lesion induction. Correlative structure-function testing may be useful for research on the functional effects of stem cell-based therapy for GA. MFERG amplitude data should be interpreted in the context of relatively high intertest variability of the rings that correspond to the central macula. Sustained choroidal insufficiency may limit long-term subretinal graft viability in this model.

Transplantation of Human Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium in a Swine Model of Geographic Atrophy

BACKGROUND

The aim of this study was to test the feasibility and safety of subretinal transplantation of human induced pluripotent stem cell (hiPSC)-derived retinal pigment epithelium (RPE) cells into the healthy margins and within areas of degenerative retina in a swine model of geographic atrophy (GA).

METHODS

Well-delimited selective outer retinal damage was induced by subretinal injection of NaIO₃ into one eye in minipigs (n = 10). Thirty days later, a suspension of hiPSC-derived RPE cells expressing green fluorescent protein was injected into the subretinal space, into the healthy margins, and within areas of degenerative retina. In vivo follow-up was performed by multimodal imaging. Post-mortem retinas were analyzed by immunohistochemistry and histology.

RESULTS

In vitro differentiated hiPSC-RPE cells showed a typical epithelial morphology, expressed RPE-related genes, and had phagocytic ability. Engrafted hiPSC-RPE cells were detected in 60% of the eyes, forming mature epithelium in healthy retina extending towards the border of the atrophy. Histological analysis revealed RPE interaction with host photoreceptors in the healthy retina. Engrafted cells in the atrophic zone were found in a patchy distribution but failed to form an epithelial-like layer.

CONCLUSIONS

These results might support the use of hiPSC-RPE cells to treat atrophic GA by providing a housekeeping function to aid the overwhelmed remnant RPE, which might improve its survival and therefore slow down the progression of GA.

Hyperreflective Foci, Optical Coherence Tomography Progression Indicators in Age-Related Macular Degeneration, Include Transdifferentiated Retinal Pigment Epithelium

Purpose

By optical coherence tomography (OCT) imaging, hyperreflective foci (HRF) indicate progression risk for advanced age-related macular degeneration (AMD) and are in part attributable to ectopic retinal pigment epithelium (RPE). We hypothesized that ectopic RPE are molecularly distinct from in-layer cells and that their cross-retinal course follows Müller glia.

Methods

In clinical OCT (61 eyes, 44 patients with AMD, 79.4 ± 7.7 years; 29 female; follow-up = 4.7 ± 0.9 years), one HRF type, RPE plume (n = 129 in 4 morphologies), was reviewed. Twenty eyes of 20 donors characterized by ex vivo OCT were analyzed by histology (normal, 4; early/intermediate AMD, 7; geographic atrophy, 6; neovascular AMD, 3). Cryosections were stained with antibodies to retinoid (RPE65, CRALPB) and immune (CD68, CD163) markers. In published RPE cellular phenotypes, red immunoreactivity was assessed semiquantitatively by one observer (none, some cells, all cells).

Results

Plume morphology evolved over time and many resolved (40%). Trajectories of RPE plume and cellular debris paralleled Müller glia, including near atrophy borders. RPE corresponding to HRF lost immunoreactivity for retinoid markers and gained immunoreactivity for immune markers. Aberrant immunoreactivity appeared in individual in-layer RPE cells and extended to all abnormal phenotypes. Müller glia remained CRALBP positive. Plume cells approached and contacted retinal capillaries.

Conclusions

HRF are indicators not predictors of overall disease activity. Gain and loss of function starts with individual in-layer RPE cells and extends to all abnormal phenotypes. Evidence for RPE transdifferentiation, possibly due to ischemia, supports a proposed process of epithelial–mesenchyme transition. Data can propel new biomarkers and therapeutic strategies for AMD.

Composition of the Inner Nuclear Layer in Human Retina

Purpose

The purpose of this study was to measure the composition of the inner nuclear layer (INL) in the central and peripheral human retina as foundation data for interpreting INL function and dysfunction.

Methods

Six postmortem human donor retinas (male and female, aged 31–56 years) were sectioned along the temporal horizontal meridian. Sections were processed with immunofluorescent markers and imaged using high-resolution, multichannel fluorescence microscopy. The density of horizontal, bipolar, amacrine, and Müller cells was quantified between 1 and 12 mm eccentricity with appropriate adjustments for postreceptoral spatial displacements near the fovea.

Results

Cone bipolar cells dominate the INL a with density near 50,000 cells/mm² at 1 mm eccentricity and integrated total ∼10 million cells up to 10 mm eccentricity. Outside central retina the spatial density of all cell populations falls but the neuronal makeup of the INL remains relatively constant: a decrease in the proportion of cone bipolar cells (from 52% at 1 mm to 37% at 10 mm) is balanced by an increasing proportion of rod bipolar cells (from 9% to 15%). The proportion of Müller cells near the fovea (17%) is lower than in the peripheral retina (27%).

Conclusions

Despite large changes in the absolute density of INL cell populations across the retina, their proportions remain relatively constant. These data may have relevance for interpreting diagnostic signals such as the electroretinogram and optical coherence tomogram.

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.

Choriocapillaris thickness and density in axially elongated eyes

PURPOSE

Axial myopia is characterized by a thinning of the choroid. We examined whether the myopic choroidal thinning also includes a thinning of the choriocapillaris.

METHODS

Using light microscopy, we measured thickness and density of the choriocapillaris at the posterior pole, posterior pole-equator midpoint (PPEMP), equator and close to the ora serrata on histological sections of 58 enucleated human globes (mean age: 62.4 ± 17.8 years; range: 24-88 years; mean axial length: 27.8 ± 4.0 mm; range: 22.0-37.0 mm).

RESULTS

Choriocapillaris thickness decreased (p < 0.001) from the posterior pole (median: 3.9 µm; interquartile range (IQR): 3.3-6.0) to the equator (median: 2.7 µm; IQR: 1.5, 4.2). It was not significantly associated with axial length, neither at the posterior pole (p = 0.25), the PPEMP (p = 0.81), equator (p = 0.80) or ora serrata (p = 0.50). Mean choriocapillaris density decreased from the posterior pole to the equator (198 µm/300 µm; IQR: 152/300, 246/300 versus 156 µm/300 µm; IQR: 72/300, 216/300; p < 0.001). Choriocapillaris density was not significantly associated with axial length (posterior pole: p = 0.07; PPEMP: p = 0.33; equator: p = 0.22; ora serrata: p = 0.36).

CONCLUSIONS

The choriocapillaris thickness and density, decreasing from the posterior pole to the fundus periphery, were not significantly associated with axial length. These findings may be of interest for the understanding of high myopia and pathologic myopia.

Local Anatomic Precursors to New-Onset Geographic Atrophy in Age-Related Macular Degeneration as Defined on OCT

PURPOSE

In macula-wide analyses, spectral-domain (SD) optical coherence tomography (OCT) features including drusen volume, hyperreflective foci, and OCT-reflective drusen substructures independently predict geographic atrophy (GA) onset secondary to age-related macular degeneration (AMD). We sought to identify SD OCT features in the location of new GA before its onset.

DESIGN

Retrospective study.

PARTICIPANTS

Age-Related Eye Disease Study 2 Ancillary SD OCT Study participants.

METHODS

We analyzed longitudinally captured SD OCT images and color photographs from 488 eyes of 488 participants with intermediate AMD at baseline. Sixty-two eyes with sufficient image quality demonstrated new-onset GA on color photographs during study years 2 through 7. The area of new-onset GA and one size-matched control region in the same eye were segmented separately, and corresponding spatial volumes on registered SD OCT images at the GA incident year and at 2, 3, and 4 years previously were defined. Differences in SD OCT features between paired precursor regions were evaluated through matched-pairs analyses.

MAIN OUTCOME MEASURES

Localized SD OCT features 2 years before GA onset.

RESULTS

Compared with paired control regions, GA precursor regions at 2, 3, and 4 years before (n = 54, 33, and 25, respectively) showed greater drusen volume (P = 0.01, P = 0.003, and P = 0.003, respectively). At 2 and 3 years before GA onset, they were associated with the presence of hypertransmission (P < 0.001 and P = 0.03, respectively), hyperreflective foci (P < 0.001 and P = 0.045, respectively), OCT-reflective drusen substructures (P = 0.004 and P = 0.03, respectively), and loss or disruption of the photoreceptor zone, ellipsoid zone, and retinal pigment epithelium (RPE, P < 0.001 and P = 0.005-0.045, respectively). At 4 years before GA onset, precursor regions were associated with photoreceptor zone thinning (P = 0.007) and interdigitation zone loss (P = 0.045).

CONCLUSIONS

Evolution to GA is heralded by early local photoreceptor changes and drusen accumulation, detectable 4 years before GA onset. These precede other anatomic heralds such as RPE changes and drusen substructure emergence detectable 1 to 2 years before GA. This study thus identified earlier end points for GA as potential therapeutic targets in clinical trials.

Evolution of oxidative stress, inflammation and neovascularization in the choroid and retina in a subretinal lipid induced age-related macular degeneration model

Oxidative stress, inflammation and neovascularization are the key pathological events that are implicated in human age-related macular degeneration (AMD). There are a limited number of animal models available for evaluating and developing new therapies. Most models represent late exudative or neovascular AMD (nAMD) but there is a relative paucity of models that mimic early events in AMD. The purpose of this study is to characterize the evolution of oxidative stress, inflammation, retinal degeneration and neovascularization in a rat model of AMD, created by subretinal injection of human lipid hydroperoxide (HpODE) that found in the sub-macular region in aged and AMD patients. Subretinal HpODE induced retinal pigment epithelium (RPE) and retinal degeneration resulting in loss of RPE cells, photoreceptors and retinal thinning. RPE degeneration and atrophy were detected by day 5, followed by neural tissue degeneration at day 12 with robust TUNEL positive cells. Western blot analysis confirmed an increase in pro-apoptotic Bak protein at day 12 in retinal tissues. Oxidative damage biomarkers (4-hydroxynonenal, malondialdehyde, 8-hydroxy-2'-deoxyguanosine, and nitrotyrosine) increased in retinal tissue from days 5-12. Müller glial activation was observed in the HpODE injected area at day 5 followed by its remodeling and migration in the outer retina by day 20. RT-qPCR analysis further indicated upregulation of pro-inflammatory genes (TNF-α, IL-1β and IL-6) both in retinal and RPE/choroidal tissue as early as day 2 and persisted until day 12. Upregulation of oxidative stress markers such as NADPH oxidase (NOX and DOUX family) was detected early in retinal tissue by day 2 followed by its upregulation in choroidal tissue at day 5. Neovascularization was demonstrated from day 12 to day 20 post HpODE injection in choroidal tissue. The results from this study indicate that subretinal HpODE induces advanced AMD phenotypes comprising many aspects of both dry/early and late) and neovascular/late AMD as observed in humans. Within 3 weeks via oxidative damage, upregulation of reactive oxygen species and pro-inflammatory genes, pro-apoptotic Bak and pro-angiogenic VEGF upregulation occurs leading to CNV formation. This experimental model of subretinal HpODE is an appropriate model for the study of AMD and provides an important platform for translational and basic research in developing new therapies particularly for early/dry AMD where currently no viable therapies are available.

Recognizing Atrophy and Mixed-Type Neovascularization in Age-Related Macular Degeneration Via Clinicopathologic Correlation

Purpose

We explored via multimodal imaging and histology an eye with mixed-types 1 and 2 macular neovascularization (MNV) and complete retinal pigment epithelium (RPE) and outer retinal atrophy (cRORA) in age-related macular degeneration.

Methods

An 82-year-old white man was followed 7 years by optical coherence tomography and treated with intravitreal anti-vascular endothelial growth factor for 3 years. At the last clinic visit, visual acuity was stable at 20/50. Two months later the patient died, and eyes were preserved at 8.33 hours after death. Submicrometer epoxy resin sections of osmicated tissue were stained with toluidine blue and evaluated by oil immersion microscopy.

Results

A shallow irregular RPE elevation on optical coherence tomography correlated with type 1 MNV with fibrocellular scar and neocapillaries (close to RPE), at a density similar to underlying native choriocapillaris (0.37 vs. 0.42). Type 2 MNV covered the native RPE and was enveloped at the margins by RPE, without neocapillaries. Native RPE cells transdifferentiated from age-normal to melanotic and entered type 1 MNV and choroid. Some photoreceptors persisted over MNV. The cRORA initiated at a collapsed druse, expanded during follow-up, and exhibited low choriocapillaris density (0.05).

Conclusions

An eye with maintained vision on 3 years of anti-vascular endothelial growth factor therapy had type 1 MNV sustaining RPE. Type 2 MNV enveloped by RPE was visible in optical coherence tomography and histology. Persistence of photoreceptors and RPE over MNV contrasted with drusen-associated cRORA.

Translational Relevance

Vision during long-term anti-vascular endothelial growth factor treatment persists by MNV partially preserving outer retinal cells and by RPE enveloping type 2 MNV.

Retinal Glial and Choroidal Vascular Pathology in Donors Clinically Diagnosed With Stargardt Disease

Purpose

The present study investigated retinal glia and choroidal vessels in flatmounts and sections from individuals with clinically diagnosed Stargardt disease (STGD).

Methods

Eyes from three donors clinically diagnosed with STGD were obtained through the Foundation Fighting Blindness (FFB). Genetic testing was performed to determine the disease-causing mutations. Eyes were enucleated and fixed in 4% paraformaldehyde and 0.5% glutaraldehyde. After imaging, retinas were dissected and immunostained for glial fibrillary acidic protein, vimentin, and peanut agglutin. Following RPE removal, the choroid was immunostained with Ulex europaeus agglutinin lectin. For each choroid, the area of affected vasculature, percent vascular area, and choriocapillaris luminal diameters were measured. The retina from one donor was hemisected and cryopreserved or embedded in JB-4 for cross-section analysis.

Results

Genetic testing confirmed the STGD diagnosis in donor 1, whereas a mutation in peripherin 2 was identified in donor 3. Genetic testing was not successful on donor 2. Therefore, only donor 1 can definitively be classified as having STGD. All donors had areas of RPE atrophy within the macular region, which correlated with underlying choriocapillaris loss. In addition, Müller cells formed pre- and subretinal membranes. Subretinal gliotic membranes correlated almost identically with RPE and choriocapillaris loss.

Conclusions

Despite bearing different genetic mutations, all donors demonstrated choriocapillaris loss and Müller cell membranes correlating with RPE loss. Müller cell remodeling was most extensive in the donor with the peripherin mutation, whereas choriocapillaris loss was greatest in the confirmed STGD donor. This study emphasizes the importance of genetic testing when diagnosing macular disease.

Local Abundance of Macular Xanthophyll Pigment Is Associated with Rod- and Cone-Mediated Vision in Aging and Age-Related Macular Degeneration

Purpose

We assessed the association between the abundance of macular xanthophyll carotenoid pigment using dual-wavelength autofluorescence and multimodal vision testing including rod-mediated dark adaptation (RMDA), a measure of retinoid re-supply, in adults ≥60 years old with and without age-related macular degeneration (AMD).

Methods

AMD severity was determined using the nine-step Age-Related Eye Disease Study grading. Tests probed cones (best-corrected visual acuity, contrast sensitivity), cones and rods (low-luminance visual acuity, low-luminance deficit, mesopic light sensitivity), or rods only (scotopic light sensitivity, RMDA). Signal attenuation by macular pigment optical density (MPOD) was estimated using a ratio of blue and green autofluorescence signal to yield mean MPOD in a 1°-diameter fovea-centered disk, mean MPOD in a 2°-diameter disk centered on a perifoveal RMDA test location, and macular pigment optical volume (MPOV, or integrated MPOD) in a 4°-diameter fovea-centered disk. Age-adjusted associations between vision and imaging measures were determined.

Results

In 88 eyes of 88 subjects (age, 74.9 ± 5.8 years) with normal eyes (n = 32), early AMD (n = 23), or intermediate AMD (n = 33), foveal and perifoveal MPOD and MPOV were higher in the AMD eyes than in the normal eyes. At the RMDA test location, higher MPOD was unrelated to AMD severity but was associated with faster RMDA.

Conclusions

In older adults with and without AMD, higher macular xanthophyll concentrations are associated with better best-corrected visual acuity and RMDA. Data are consistent with a model of cone resilience and rod vulnerability in aging and AMD and can be further explored in a larger sample study.

Apigenin Protects Mouse Retina against Oxidative Damage by Regulating the Nrf2 Pathway and Autophagy

Oxidative stress is a critical factor in the pathology of age-related macular degeneration (AMD). Apigenin (AP) is a flavonoid with an outstanding antioxidant activity. We had previously observed that AP protected APRE-19 cells against oxidative injury in vitro. However, AP has poor water and fat solubility, which determines its low oral bioavailability. In this study, we prepared the solid dispersion of apigenin (AP-SD). The solubility and dissolution of AP-SD was significantly better than that of the original drug, so the oral bioavailability in rats was better than that of the original drug. Then, the effects of AP-SD on the retina of a model mouse with dry AMD were assessed by fundus autofluorescence (FAF), optical coherence tomography (OCT), and electron microscopy; the results revealed that AP-SD alleviated retinopathy. Further research found that AP-SD promoted the nuclear translocation of Nrf2 and increased expression levels of the Nrf2 and target genes HO-1 and NQO-1. AP-SD enhanced the activities of SOD and GSH-Px and decreased the levels of ROS and MDA. Furthermore, AP-SD upregulated the expressions of p62 and LC3II in an Nrf2-dependent manner. However, these effects of AP-SD were observed only in the retina of Nrf2 WT mice, not in Nrf2 KO mice. In addition, the therapeutic effect of AP-SD was dose dependent, and AP did not work. In conclusion, AP-SD significantly enhanced the bioavailability of the original drug and reduced retinal oxidative injury in the model mouse of dry AMD in vivo. The results of the underlying mechanism showed that AP-SD upregulated the expression of antioxidant enzymes through the Nrf2 pathway and upregulated autophagy, thus inhibiting retinal oxidative damage. AP-SD may be a potential compound for the treatment of dry AMD.

Neurodegeneration, gliosis, and resolution of haemorrhage in neovascular age-related macular degeneration, a clinicopathologic correlation

BACKGROUND

To analyse cellular and spatiotemporal factors of neurodegeneration and gliosis in a patient with submacular haemorrhage (SMH) secondary to type 1 macular neovascularization in neovascular age-related macular degeneration (nAMD).

METHODS

This is a case study and clinicopathologic correlation of an 84-year-old white man with nAMD treated with antiangiogenic drugs and photodynamic therapy during a 6-year follow-up. Eyes were recovered for histology 8.23 h after death. In vivo multimodal imaging including optical coherence tomography (OCT) and en face modalities was compared with ex vivo OCT and high-resolution histologic images, using a custom image registration procedure. SMH components were defined (intraretinal, subretinal, sub-retinal pigment epithelium (RPE), and dehemoglobinized blood). Neurodegenerative changes in each of these areas were described. One anonymous donor eye with haemorrhagic nAMD was also reviewed as a comparator.

RESULTS

By in vivo OCT, progressive resolution of the haemorrhage and gradual transformation of sub-RPE fluid to fibrous hyperreflective tissue, progressive macular atrophy, and variation in external limiting membrane (ELM) visibility were observed. Histology showed intense photoreceptor loss with preservation and self-adhesion of macular Müller glia resulting in ELM condensation. The comparator eye exhibited shed cone inner segments among subretinal erythrocytes.

CONCLUSION

This is the most detailed clinicopathologic correlation of nAMD with SMH resolution to date, and the first in the OCT era. Our results reveal profound macular neurodegeneration and gliosis, signified by condensed ELM, soon after haemorrhage begins. Intensified OCT reflectivity of the ELM, an important retinal barrier, has potential as a biomarker for severe photoreceptor loss and gliosis.

CLINICOPATHOLOGIC CORRELATION OF GEOGRAPHIC ATROPHY SECONDARY TO AGE-RELATED MACULAR DEGENERATION

Supplemental Digital Content is Available in the Text.

Direct clinicopathologic correlation of an eye with geographic atrophy secondary to age-related macular degeneration provides histologic correlates of features commonly seen by optical coherence tomography, such as end-stages of drusen, subretinal drusenoid deposit, plaques near the Bruch membrane, and hyporeflective wedge.

Purpose:

In an eye with geographic atrophy (GA) secondary to age-related macular degeneration, we correlated ex vivo histologic features with findings recorded in vivo using optical coherence tomography (OCT), near-infrared reflectance imaging, and fundus autofluorescence.

Methods:

In the left eye of an 86-year-old white woman, in vivo near-infrared reflectance and eye-tracked OCT B-scans at each of 6 clinic visits and a baseline fundus autofluorescence image were correlated with high-resolution histologic images of the preserved donor eye.

Results:

Clinical imaging showed a small parafoveal multilobular area of GA, subfoveal soft drusen, refractile drusen, hyperreflective lines near the Bruch membrane, subretinal drusenoid deposit (reticular pseudodrusen), and absence of hyperautofluorescent foci at the GA margin. By histology, soft drusen end-stages included avascular fibrosis with highly reflective cholesterol crystals. These accounted for hyperreflective lines near the Bruch membrane in OCT and plaques in near-infrared reflectance imaging. Subretinal drusenoid deposit was thick, continuous, extracellular, extensive outside the fovea, and associated with distinctive retinal pigment epithelium dysmorphia and photoreceptor degeneration. A hyporeflective wedge corresponded to ordered Henle fibers without cellular infiltration. The external limiting membrane descent, which delimits GA, was best visualized in high-quality OCT B-scans. Retinal pigment epithelium and photoreceptor changes at the external limiting membrane descent were consistent with our recent histologic survey of donor eyes.

Conclusion:

This case informs on the extent, topography, and lifecycle of extracellular deposits. High-quality OCT scans are required to reveal all tissue features relevant to age-related macular degeneration progression to GA, especially the external limiting membrane descent. Histologically validated signatures of structural OCT B-scans can serve as references for other imaging modalities.

Subretinal pseudocysts: A novel OCT finding in diabetic macular edema

Purpose

to report the presence of a new structural optical coherence tomography (OCT) finding, namely subretinal pseudocysts, in a patient affected by diabetic retinopathy (DR).

Observations

A 52-year-old man affected by type 2 diabetes from 10 years was referred to our department complaining of a visual decline in both eyes. Best corrected visual acuity was 20/100 and 20/80 in the right and left eye, respectively. Fundus examination, fluorescein angiography, and structural OCT revealed the presence of a proliferative DR with diabetic macular edema in both eyes. Interestingly, structural OCT showed subretinal pseudocystic spaces inside the subretinal fluid of the macular neuroretinal detachment.

Conclusions and importance

Subretinal pseudocysts are a new structural OCT entity. We reported for the first time the evidence that pseudocysts may develop in the subretinal space in a case of diabetic macular edema.

p62 /SQSTM1 coding plasmid prevents age related macular degeneration in a rat model

P62/SQSTM1, a multi-domain protein that regulates inflammation, apoptosis, and autophagy, has been linked to age-related pathologies. For example, previously we demonstrated that administration of p62/SQSTM1-encoding plasmid reduced chronic inflammation and alleviated osteoporosis and metabolic syndrome in animal models. Herein, we built upon these findings to investigate effect of the p62-encoding plasmid on an age-related macular degeneration (AMD), a progressive neurodegenerative ocular disease, using spontaneous retinopathy in senescence-accelerated OXYS rats as a model. Overall, the p62DNA decreased the incidence and severity of retinopathy. In retinal pigment epithelium (RPE), p62DNA administration slowed down development of the destructive alterations of RPE cells, including loss of regular hexagonal shape, hypertrophy, and multinucleation. In neuroretina, p62DNA prevented gliosis, retinal thinning, and significantly inhibited microglia/macrophages migration to the outer retina, prohibiting their subretinal accumulation. Taken together, our results suggest that the p62DNA has a strong retinoprotective effect in AMD.

Incomplete Retinal Pigment Epithelial and Outer Retinal Atrophy in Age-Related Macular Degeneration: Classification of Atrophy Meeting Report 4

PURPOSE

To describe the defining features of incomplete retinal pigment epithelium (RPE) and outer retinal atrophy (iRORA), a consensus term referring to the OCT-based anatomic changes often identified before the development of complete RPE and outer retinal atrophy (cRORA) in age-related macular degeneration (AMD). We provide descriptive OCT and histologic examples of disease progression.

DESIGN

Consensus meeting.

PARTICIPANTS

Panel of retina specialists, including retinal imaging experts, reading center leaders, and retinal histologists.

METHODS

As part of the Classification of Atrophy Meeting (CAM) program, an international group of experts analyzed and discussed longitudinal multimodal imaging of eyes with AMD. Consensus was reached on a classification system for OCT-based structural alterations that occurred before the development of atrophy secondary to AMD. New terms of iRORA and cRORA were defined. This report describes in detail the CAM consensus on iRORA.

MAIN OUTCOME MEASURES

Defining the term iRORA through OCT imaging and longitudinal cases showing progression of atrophy, with histologic correlates.

RESULTS

OCT was used in cases of early and intermediate AMD as the base imaging method to identify cases of iRORA. In the context of drusen, iRORA is defined on OCT as (1) a region of signal hypertransmission into the choroid, (2) a corresponding zone of attenuation or disruption of the RPE, and (3) evidence of overlying photoreceptor degeneration. The term iRORA should not be used when there is an RPE tear. Longitudinal studies confirmed the concept of progression from iRORA to cRORA.

CONCLUSIONS

An international consensus classification for OCT-defined anatomic features of iRORA are described and examples of longitudinal progression to cRORA are provided. The ability to identify these OCT changes reproducibly is essential to understand better the natural history of the disease, to identify high-risk signs of progression, and to study early interventions. Longitudinal data are required to quantify the implied risk of vision loss associated with these terms. The CAM classification provides initial definitions to enable these future endeavors, acknowledging that the classification will be refined as new data are generated.

HISTOLOGY OF GEOGRAPHIC ATROPHY SECONDARY TO AGE-RELATED MACULAR DEGENERATION: A Multilayer Approach

Supplemental Digital Content is Available in the Text.

High-resolution histology at the border of geographic atrophy (or complete retinal pigment epithelium and outer retinal atrophy) secondary to age-related macular degeneration reveals marked gliosis and near-total photoreceptor depletion, abundant extracellular deposits, and long-standing abnormalities of Bruch membrane and choriocapillaris, indicating severe and potentially irreversible tissue damage at this stage of the disease.

Purpose:

To systematically characterize histologic features of multiple chorioretinal layers in eyes with geographic atrophy, or complete retinal pigment epithelium (RPE) and outer retinal atrophy, secondary to age-related macular degeneration, including Henle fiber layer and outer nuclear layer; and to compare these changes to those in the underlying RPE-Bruch membrane—choriocapillaris complex and associated extracellular deposits.

Methods:

Geographic atrophy was delimited by the external limiting membrane (ELM) descent towards Bruch membrane. In 13 eyes, histologic phenotypes and/or thicknesses of Henle fiber layer, outer nuclear layer, underlying supporting tissues, and extracellular deposits at four defined locations on the non-atrophic and atrophic sides of the ELM descent were assessed and compared across other tissue layers, with generalized estimating equations and logit models.

Results:

On the non-atrophic side of the ELM descent, distinct Henle fiber layer and outer nuclear layer became dyslaminated, cone photoreceptor inner segment myoids shortened, photoreceptor nuclei and mitochondria translocated inward, and RPE was dysmorphic. On the atrophic side of the ELM descent, all measures of photoreceptor health declined to zero. Henle fiber layer/outer nuclear layer thickness halved, and only Müller cells remained, in the absence of photoreceptors. Sub-RPE deposits remained, Bruch membrane thinned, and choriocapillaris density decreased.

Conclusion:

The ELM descent sharply delimits an area of marked gliosis and near-total photoreceptor depletion clinically defined as Geographic atrophy (or outer retinal atrophy), indicating severe and potentially irreversible tissue damage. Degeneration of supporting tissues across this boundary is gradual, consistent with steady age-related change and suggesting that RPE and Müller cells subsequently respond to a threshold of stress. Novel clinical trial endpoints should be sought at age-related macular degeneration stages before intense gliosis and thick deposits impede therapeutic intervention.

Müller cells in pathological retinal angiogenesis

Müller cells are the major glial cells spanning the entire layer of the retina and maintaining retinal structure. Under pathological conditions, Müller cells are involved in retinal angiogenesis, a process of growing new blood vessels from pre-existing capillaries. In response to hypoxia, high glucose, and inflammation conditions, multiple signaling pathways are activated in Müller cells, followed by the increased production of proangiogenic factors including vascular endothelial growth factor, basic fibroblast growth factor, matrix metalloproteinases, Netrin-4, and angiopoietin-like 4. Expression of antiangiogenic factors is also downregulated in Müller cells. Besides, proliferation and dedifferentiation of Müller cells facilitates retinal angiogenesis. In this review, we summarized molecular mechanisms of Müller cells-related retinal angiogenesis. The potential of Müller cells as a therapeutic target for retinal angiogenesis was also discussed.

Subretinal pseudocyst: A novel optical coherence tomography finding in age-related macular degeneration

Purpose:

To report the presence of a new structural optical coherence tomography finding, namely, subretinal pseudocysts, in a patient affected by age-related macular degeneration.

Methods:

Case report including multimodal imaging discussion.

Case Report:

We report a case of a 77-year-old woman affected by age-related macular degeneration from 7 years. Best corrected visual acuity was counting fingers and 20/40 in the right and left eye, respectively. The left eye was affected by type 1 macular neovascularization treated by 34 intravitreal injections of anti-vascular endothelial growth factor (22 ranibizumab and 12 aflibercept injections). Interestingly, structural optical coherence tomography showed the persistence of a subretinal cystoid space (i.e. ‘subretinal pseudocyst’) after the last anti-vascular endothelial growth factor treatment, even in absence of other signs of exudation.

Conclusions:

Subretinal pseudocysts are a new structural optical coherence tomography entity. We reported for the first time the evidence that pseudocysts may develop in the subretinal space in a case of age-related macular degeneration.

Blood-retina barrier failure and vision loss in neuron-specific degeneration

Changes in neuronal activity alter blood flow to match energy demand with the supply of oxygen and nutrients. This functional hyperemia is maintained by interactions between neurons, vascular cells, and glia. However, how changing neuronal activity prevalent at the onset of neurodegenerative disease affects neurovascular elements is unclear. Here, in mice with photoreceptor degeneration, a model of neuron-specific dysfunction, we combined assessment of visual function, neurovascular unit structure, and the blood-retina barrier permeability. We found that the rod loss paralleled remodeling of the neurovascular unit, comprised of photoreceptors, retinal pigment epithelium, and Muller glia. When significant visual function was still present, blood flow became disrupted and blood-retina barrier began to fail, facilitating cone loss and vision decline. Thus, in contrast to the established view, vascular deficit in neuronal degeneration is not a late consequence of neuronal dysfunction, but is present early in the course of disease. These findings further establish the importance of vascular deficit and blood retina barrier function in neuron-specific loss, and highlight it as a target for early therapeutic intervention.

Ultrastructural analysis of submacular choriocapillaris and its transport systems in AMD and aged control eyes

The choriocapillaris is the source of nutrients and oxygen for photoreceptors, which consume more oxygen per gram of tissue than any other cell in the body. The purpose of this study was to evaluate and compare the ultrastructure of the choriocapillaris and its transport systems in patients with and without age-related macular degeneration (AMD). Ultrastructural changes were also evaluated in subjects that were homozygous for polymorphisms in high risk CFH alleles (Pure 1) only or homozygous only for high risk ARMS2/HTRA1 (Pure 10) alleles. Tissue samples were obtained from the macular region of forty male (n = 24) and female (n = 16) donor eyes and prepared for ultrastructural studies with transmission electron microscopy (TEM). The average age of the aged donors was 74 ± 7.2 (n = 30) and the young donors 31.7 ± 11.25 (n = 10). There was no significant difference in average ages between the adult groups. TEM images of the capillaries in the choriocapillaris (CC) were taken at 4,000X and 25,000X and used to measure the area of endothelial cell somas, the number of fenestrations, and area of caveolae within the endothelial cells per length of Bruchs membrane (BrMb). The Student t-test and Wilcoxon sum rank test were used to determine significant differences. There was no significant difference between young subjects and aged controls in any of the morphological criteria assessed. There was a significant decrease in the number of fenestrations/mm of BrMb in atrophic areas of GA eyes (p = 0.007) when compared with aged control eyes. A significant increase was found in the caveolae area as a percent of the endothelial cell soma of capillaries from GA subjects as compared with the controls (p = 0.03). Loss of capillary segments in choriocapillaris was also evident, especially in areas of geographic atrophy and CNV. In eyes from patients with sequence variations, the capillary endothelial cells often appeared degenerative and exhibited atypical fenestrations and pericytes covering the blood vessels. Subjects that were homozygous for polymorphisms in high risk CFH alleles only had more fenestrations/mm of BrMb than subjects that were homozygous only for high risk ARMS2/HTRA1 alleles (p = 0.04), while the latter had greater caveolae area/endothelial cell area than the former (p = 0.007). This study demonstrated an attenuation of CC and a significant decline in the two major transport systems in CC endothelial cells in AMD. This may contribute to drusen deposition, nutrient transport, and vision loss in AMD subjects.

Soft Drusen in Age-Related Macular Degeneration: Biology and Targeting Via the Oil Spill Strategies

AMD is a major cause of legal blindness in older adults approachable through multidisciplinary research involving human tissues and patients. AMD is a vascular-metabolic-inflammatory disease, in which two sets of extracellular deposits, soft drusen/basal linear deposit (BLinD) and subretinal drusenoid deposit (SDD), confer risk for end-stages of atrophy and neovascularization. Understanding how deposits form can lead to insights for new preventions and therapy. The topographic correspondence of BLinD and SDD with cones and rods, respectively, suggest newly realized exchange pathways among outer retinal cells and across Bruch's membrane and the subretinal space, in service of highly evolved, eye-specific physiology. This review focuses on soft drusen/BLinD, summarizing evidence that a major ultrastructural component is large apolipoprotein B,E-containing, cholesterol-rich lipoproteins secreted by the retinal pigment epithelium (RPE) that offload unneeded lipids of dietary and outer segment origin to create an atherosclerosis-like progression in the subRPE-basal lamina space. Clinical observations and an RPE cell culture system combine to suggest that soft drusen/BLinD form when secretions of functional RPE back up in the subRPE-basal lamina space by impaired egress across aged Bruch's membrane-choriocapillary endothelium. The soft drusen lifecycle includes growth, anterior migration of RPE atop drusen, then collapse, and atrophy. Proof-of-concept studies in humans and animal models suggest that targeting the “Oil Spill in Bruch's membrane” offers promise of treating a process in early AMD that underlies progression to both end-stages. A companion article addresses the antecedents of soft drusen within the biology of the macula.

An Acute Injury Model for the Phenotypic Characteristics of Geographic Atrophy

Purpose

Geographic atrophy (GA) is the late stage of non-neovascular age-related macular degeneration. A lack of animal models for GA has hampered treatment efforts. Presented herein is a rat model for GA using subretinal injection of sodium iodate (NaIO₃).

Methods

Rats were given subretinal injections of NaIO₃ (5 μg/μL) using a pico-injector. Fundus photographs and spectral domain optical coherent tomography scans were collected at 1, 3, 7, 14, and 28 days after injection, at which time rats were euthanized and eyes were enucleated. Eyes were either cryopreserved or dissected into retinal and choroidal flatmounts. Fluorescence immunohistochemistry was performed for retinal glial fibrillary acidic protein (activated Müller cells and astrocytes) and vimentin (Müller cells), as well as peanut agglutin lectin (photoreceptors) labeling. RPE/choroids were labeled for RPE65 and CD34. Images were collected on Zeiss confocal microscopes.

Results

Fundus photos, spectral domain optical coherent tomography, and RPE65 staining revealed well-demarcated areas with focal loss of RPE and photoreceptors in NaIO₃-treated rats. At 1 day after injection, RPE cells appeared normal. By 3 days, there was patchy RPE and photoreceptor loss in the injected area. RPE and photoreceptors were completely degenerated in the injected area by 7 days. A large subretinal glial membrane occupied the degenerated area. Choriocapillaris was highly attenuated in the injected area at 14 and 28 days.

Conclusions

The rat model reported herein mimics the photoreceptor cell loss, RPE atrophy, glial membrane formation, and choriocapillaris degeneration seen in GA. This model will be valuable for developing and testing drugs and progenitor cell regenerative therapies for GA.