Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography

Retinal structural alterations in patients with epilepsy taking antiepileptic drugs: A systematic review and meta-analysis of OCT findings

The impact of various neurodegenerative diseases on the retina has been investigated in recent years using optical coherence tomography (OCT). Epilepsy, classified as a neurodegenerative disorder, has been indicated to affect the structural integrity of the retina. Moreover, there is ongoing debate regarding the relative contribution of the disease pathogenesis and the consumption of anti-epileptic drugs (AEDs) to these retinal changes. The lack of systematic reviews has hindered our understanding of the true effects of epilepsy and AEDs on retinal health, as well as the efficacy of OCT in detecting these alterations. To comprehensively review the impact of epilepsy and AEDs on the structure of retina, we thoroughly searched the PubMed, EMBASE, and Web of Science databases to identify relevant articles published until July 7, 2024, and performed a meta-analysis. We updated our search in November, 2024. Random effect models have been used to calculate pooled effect estimates. Nineteen studies with a total number of 1851 eyes were identified. Adult patients showed significant reduction with respect of retinal nerve fiber layer (RNFL) thickness; average, as well as all quadrants. Significant reductions were also detected in all quadrants of ganglion cell complex (GCC). Conversely, average GCC and central macular thickness did not differ significantly between cases and controls. Additionally, in terms of various volume measurements in the retina, significant losses were observed in macular RNFL, ganglion cell-inner plexiform layer and total macula volumes in adult patients. In contrast, the inner nuclear layer volume remained comparable between the 2 groups. In pediatric patients with epilepsy receiving valproic acid, significant reductions was observed in the average RNFL thickness, as well as in the nasal and inferior quadrants; however, there were no significant changes in the thickness of the superior and temporal quadrants of RNFL, nor in foveal thickness. The analysis of pediatric patients receiving levetiracetam indicated no significant changes in retinal structural measurements across various RNFL categories, or in foveal thickness. This meta-analysis revealed the structural retinal alterations following AEDs administration in patients with epilepsy (PwE). OCT appears to be a reliable device that reflects retinal toxicity with AED consumption in PwE.

A Narrowband 635 nm Autofluorescence Peak in Albino Mouse Eyes Found With Multi-Modal Imaging Reveals the Presence of Protoporphyrin IX in the Choroid

Purpose

To investigate differences in fundus autofluorescence (AF) spectra of pigmented (C57Bl/6) and albino (Balb/c) mouse retinas.

Methods

AF spectra were measured with a scanning laser ophthalmoscope (SLO) with a high-resolution spectrometer. The action spectrum of a 635 nm AF "spike" in albino mice was measured to estimate the underlying absorption spectrum. Optical coherence tomography (OCT) and OCT angiography were used to determine the most likely depth location of the source of the AF feature.

Results

Two narrowband emission peaks centered at 635 nm and ∼705 nm were observed in the AF spectra of albino (but not pigmented) mouse eyes. The dual-peak emission spectrum of the albino eye was extracted by subtracting a broadband emission that was similar in pigmented and albino mice: the two peaks correspond to emission spectra peaks of protoporphyrin IX, an obligate precursor in the biosynthesis of heme and cytochrome c. The action spectrum of the prominent 635 nm emission component corresponded with the PPIX absorption spectrum. The spatial distribution of the 635 nm emission did not correspond to that of the retinal vasculature but had a pattern more consistent with a choroidal origin.

Conclusions

Our results reveal that substantial PPIX is present in the posterior tissues of albino (Balb/c) mouse eyes, and measurable with high-resolution spectral measurements, and suggest that the absence of the narrow band PPIX emission peaks in pigmented eyes arises at least in part from screening by RPE and choroidal melanin.

In Vivo Imaging of Cobalt-Induced Ocular Toxicity in a Mouse Model

Cobalt is a trace element, crucial for red blood cell formation and neurological function. Cobalt toxicity is often only diagnosed after severe manifestations, including visual impairment. We aimed to investigate whether optical coherence tomography (OCT) and magnetic resonance imaging (MRI) can effectively detect cobalt-induced ocular toxicity in a murine model. Five wild-type mice (WT, C57Bl6) received daily intraperitoneal cobalt chloride injections for 28 days with a dosage of 12.5 mg/kg. Another 5 WT mice served as controls. After 28 days, all mice underwent manganese contrast-enhanced MRI and OCT examinations. Macroscopic and histological analysis of the enucleated eyes were performed. MRI revealed an increased signal in the optic nerves of injected mice. Anterion OCT provided in vivo visualization of the entire eye, demonstrating incipient cataract formation in the cobalt-injected mice. Both Spectralis domain OCT and Anterion, followed by histological analyses, confirmed preserved retinal structure with decreased thickness in the cobalt-injected group, with only minor neuronal damage and cell loss. Optic nerve analysis demonstrated myelin loss and increased inflammation with high levels of reactive gliosis. This study demonstrates optic neuropathy induced by cobalt toxicity, as shown by increased optic nerve signal on MRI without significant retinopathy. Anterion OCT showed incipient cataracts in the anterior segment.

In Vivo Imaging of Rodent Retina in Retinal Disease

High-quality imaging of the retina is crucial to the diagnosis and monitoring of disease, as well as for evaluating the success of therapeutics in human patients and in preclinical animal models. Here, we describe the basic principles and methods for in vivo retinal imaging in rodents, including fundus imaging, fluorescein angiography, optical coherence tomography, fundus autofluorescence, and infrared imaging. After providing a concise overview of each method and detailing the retinal diseases and conditions that can be visualized through them, we will proceed to discuss the advantages and disadvantages of each approach. These protocols will facilitate the acquisition of optimal images for subsequent quantification and analysis. Additionally, a brief explanation will be given regarding the potential results and the clinical significance of the detected abnormalities.

SLC16A8 is a causal contributor to age-related macular degeneration risk

Age-related macular degeneration (AMD), a complex neurodegenerative disease, is a leading cause of visual impairment worldwide with a strong genetic component. Genetic studies have identified several loci, but few causal genes with functional characterization. Here we highlight multiple lines of evidence which show a causal role in AMD for SLC16A8, which encodes MCT3, a retinal pigment epithelium (RPE) specific lactate transporter. First, in an unbiased, genome-wide analysis of rare coding variants we show multiple SLC16A8 rare variants are associated with AMD risk, corroborating previous borderline significant reports from AMD rare variant studies. Second, we report a novel SLC16A8 mutation in a three-generation family with early onset macular degeneration. Finally, mis-expression in multiple model organisms shows functional and anatomic retinal consequences. This study highlights the important role for SLC16A8 and lactate regulation towards outer retina/RPE health and highlights a potential new therapeutic opportunity for the treatment of AMD.

In vivo volumetric analysis of retinal vascular hemodynamics in mice with spatio-temporal optical coherence tomography

Significance

Microcirculation and neurovascular coupling are important parameters to study in neurological and neuro-ophthalmic conditions. As the retina shares many similarities with the cerebral cortex and is optically accessible, a special focus is directed to assessing the chorioretinal structure, microvasculature, and hemodynamics of mice, a vital animal model for vision and neuroscience research.

Aim

We aim to introduce an optical imaging tool enabling in vivo volumetric mouse retinal monitoring of vascular hemodynamics with high temporal resolution.

Approach

We translated the spatio-temporal optical coherence tomography (STOC-T) technique into the field of small animal imaging by designing a new optical system that could compensate for the mouse eye refractive error. We also developed post-processing algorithms, notably for the assessment of (i) localized hemodynamics from the analysis of pulse wave-induced Doppler artifact modulation and (ii) retinal tissue displacement from phase-sensitive measurements.

Results

We acquired high-quality, in vivo volumetric mouse retina images at a rate of 113 Hz over a lateral field of view of ∼ 500    μ m . We presented high-resolution en face images of the retinal and choroidal structure and microvasculature from various layers, after digital aberration correction. We were able to measure the pulse wave velocity in capillaries of the outer plexiform layer with a mean speed of 0.35 mm/s and identified venous and arterial pulsation frequency and phase delay. We quantified the modulation amplitudes of tissue displacement near major vessels (with peaks of 150 nm), potentially carrying information about the biomechanical properties of the retinal layers involved. Last, we identified the delays between retinal displacements due to the passing of venous and arterial pulse waves.

Conclusions

The developed STOC-T system provides insights into the hemodynamics of the mouse retina and choroid that could be beneficial in the study of neurovascular coupling and vasculature and flow speed anomalies in neurological and neuro-ophthalmic conditions.

In vivo multi-contrast depth-resolved choroidal imaging of a mouse using polarization-diversity optical coherence tomography

The results of depth-resolved multi-contrast in vivo mouse choroidal imaging using a polarization-diversity optical coherence tomography (PD-OCT) system are presented. A selectively chosen depth of focus that was fine-tuned with a sensorless adaptive optics technique and a simple segmentation based on the degree of polarization uniformity signal visualizes the detailed features of a mouse choroid from the OCT angiography images. A comprehensive image analysis of the choroid revealed the distinctive pathological characteristics of the laser-induced choroidal neovascularization mouse.

Age-Related Retinal Layer Thickness Changes Measured by OCT in APPNL-F/NL-F Mice: Implications for Alzheimer's Disease

In Alzheimer's disease (AD), transgenic mouse models have established links between abnormalities in the retina and those in the brain. APPNL-F/NL-F is a murine, humanized AD model that replicates several pathological features observed in patients with AD. Research has focused on obtaining quantitative parameters from optical coherence tomography (OCT) in AD. The aim of this study was to analyze, in a transversal case-control study using manual retinal segmentation via SD-OCT, the changes occurring in the retinal layers of the APPNL/F-NF/L AD model in comparison to C57BL/6J mice (WT) at 6, 9, 12, 15, 17, and 20 months of age. The analysis focused on retinal thickness in RNFL-GCL, IPL, INL, OPL, and ONL based on the Early Treatment Diabetic Retinopathy Study (ETDRS) sectors. Both APPNL-F/NL-F-model and WT animals exhibited thickness changes at the time points studied. While WT showed significant changes in INL, OPL, and ONL, the AD model showed changes in all retinal layers analyzed. The APPNL-F/NL-F displayed significant thickness variations in the analyzed layers except for the IPL compared to related WT. These thickness changes closely resembled those found in humans during preclinical stages, as well as during mild and moderate AD stages, making this AD model behave more similarly to the disease in humans.

OCT Intensity of the Region between Outer Retina Band 2 and Band 3 as a Biomarker for Retinal Degeneration and Therapy

Optical coherence tomography (OCT) is widely used to probe retinal structure and function. This study investigated the outer retina band (ORB) pattern and reflective intensity for the region between bands 2 and 3 (Dip) in three mouse models of inherited retinal degeneration (Rs1KO, TTLL5KO, RPE65KO) and in human AMD patients from the A2A database. OCT images were manually graded, and reflectivity signals were used to calculate the Dip ratio. Qualitative analyses demonstrated the progressive merging band 2 and band 3 in all three mouse models, leading to a reduction in the Dip ratio compared to wildtype (WT) controls. Gene replacement therapy in Rs1KO mice reverted the ORB pattern to one resembling WT and increased the Dip ratio. The degree of anatomical rescue in these mice was highly correlated with level of transgenic RS1 expression and with the restoration of ERG b-wave amplitudes. While the inner retinal cavity was significantly enlarged in dark-adapted Rs1KO mice, the Dip ratio was not altered. A reduction of the Dip ratio was also detected in AMD patients compared with healthy controls and was also positively correlated with AMD severity on the AMD score. We propose that the ORB and Dip ratio can be used as non-invasive early biomarkers for retina health, which can be used to probe therapeutic gene expression and to evaluate the effectiveness of therapy.

The Mongolian gerbil as an advanced model to study cone system physiology

In this work, we introduce a diurnal rodent, the Mongolian gerbil (Meriones unguiculatus) (MG) as an alternative to study retinal cone system physiology and pathophysiology in mice. The cone system is of particular importance, as it provides high-acuity and color vision and its impairment in retinal disorders is thus especially disabling. Despite their nocturnal lifestyle, mice are currently the most popular animals to study cone-related diseases due to the high availability of genetically modified models. However, the potential for successful translation of any cone-related results is limited due to the substantial differences in retinal organization between mice and humans. Alternatively, there are diurnal rodents such as the MG with a higher retinal proportion of cones and a macula-like specialized region for improved visual resolution, the visual streak. The focus of this work was the evaluation of the MG's cone system functionality using full-field electroretinography (ERG), together with a morphological assessment of its retinal/visual streak organization via angiography, optical coherence tomography (OCT), and photoreceptor immunohistochemistry. We found that rod system responses in MGs were comparable or slightly inferior to mice, while in contrast, cone system responses were much larger, more sensitive, and also faster than those in the murine counterparts, and in addition, it was possible to record sizeable ON and OFF ERG components. Morphologically, MG cone photoreceptor opsins were evenly distributed throughout the retina, while mice show a dorsoventral M- and S-opsin gradient. Additionally, each cone expressed a single opsin, in contrast to the typical co-expression of opsins in mice. Particular attention was given to the visual streak region, featuring a higher density of cones, elongated cone and rod outer segments (OSs), and an increased thickness of the inner and outer retinal layers in comparison to peripheral regions. In summary, our data render the MG a supreme model to investigate cone system physiology, pathophysiology, and to validate potential therapeutic strategies in that context.

An innovative multi-modal retinal imaging system for in vivo retinal detection in small animals

This paper presents an innovative retinal imaging system tailored for in vivo fundus detection in small animals. This system integrates Scanning Laser Ophthalmoscopy (SLO) and optical Coherence Tomography (OCT) techniques, enabling the simultaneous generation of images from various modalities, including SLO reflectance, SLO fluorescein angiogram, OCT, and OCT angiogram. The existing multi-modal retinal imaging systems generally encounter limitations such as the inability to detect peripheral lesion areas attributed to small Field of View (FOV) design and susceptibility to sample motion due to slow data acquisition speed. To address these challenges, it's essential to underscore that this proposed system offers a range of notable advantages, including its compact design, the capacity for widefield imaging with a FOV of up to 100°, and a rapid OCT A-scan rate of 250 kHz, notably exceeding the capabilities of pre-existing multi-modal retinal imaging systems. Validation of the system involved imaging the eyes of normal wild-type mice and diseased mice afflicted with retinal detachment and choroidal neovascularization (CNV). The favorable imaging results demonstrate the system's reliability in identifying retinal lesions in small animals.

Mural Serum Response Factor (SRF) Deficiency Provides Insights into Retinal Vascular Functionality and Development

Serum response factor (SRF) controls the expression of muscle contraction and motility genes in mural cells (MCs) of the vasculature. In the retina, MC-SRF is important for correct angiogenesis during development and the continuing maintenance of the vascular tone. The purpose of this study was to provide further insights into the effects of MC SRF deficiency on the vasculature and function of the mature retina in SrfiMCKO mice that carry a MC-specific deletion of Srf. Retinal morphology and vascular integrity were analyzed in vivo via scanning laser ophthalmoscopy (SLO), angiography, and optical coherence tomography (OCT). Retinal function was evaluated with full-field electroretinography (ERG). We found that retinal blood vessels of these mutants exhibited different degrees of morphological and functional alterations. With increasing severity, we found vascular bulging, the formation of arteriovenous (AV) anastomoses, and ultimately, a retinal detachment (RD). The associated irregular retinal blood pressure and flow distribution eventually induced hypoxia, indicated by a negative ERG waveform shape. Further, the high frequency of interocular differences in the phenotype of individual SrfiMCKO mice points to a secondary nature of these developments far downstream of the genetic defect and rather dependent on the local retinal context.

Gene-agnostic approaches to treating inherited retinal degenerations

Most patients with inherited retinal degenerations (IRDs) have been waiting for treatments that are "just around the corner" for decades, with only a handful of seminal breakthroughs happening in recent years. Highlighting the difficulties in the quest for curative therapeutics, Luxturna required 16 years of development before finally obtaining United States Food and Drug Administration (FDA) approval and its international equivalents. IRDs are both genetically and phenotypically heterogeneous. While this diversity offers many opportunities for gene-by-gene precision medicine-based approaches, it also poses a significant challenge. For this reason, alternative (or parallel) strategies to identify more comprehensive, across-the-board therapeutics for the genetically and phenotypically diverse IRD patient population are very appealing. Even when gene-specific approaches may be available and become approved for use, many patients may have reached a disease stage whereby these approaches may no longer be viable. Thus, alternate visual preservation or restoration therapeutic approaches are needed at these stages. In this review, we underscore several gene-agnostic approaches that are being developed as therapeutics for IRDs. From retinal supplementation to stem cell transplantation, optogenetic therapy and retinal prosthetics, these strategies would bypass at least in part the need for treating every individual gene or mutation or provide an invaluable complement to them. By considering the diverse patient population and treatment strategies suited for different stages and patterns of retinal degeneration, gene agnostic approaches are very well poised to impact favorably outcomes and prognosis for IRD patients.

Retinal Phenotyping of a Murine Model of Lafora Disease

Lafora disease (LD) is a progressive neurologic disorder caused by biallelic pathogenic variants in EPM2A or EPM2B, leading to tissue accumulation of polyglucosan aggregates termed Lafora bodies (LBs). This study aimed to characterize the retinal phenotype in Epm2a−/− mice by examining knockout (KO; Epm2a−/−) and control (WT) littermates at two time points (10 and 14 months, respectively). In vivo exams included electroretinogram (ERG) testing, optical coherence tomography (OCT) and retinal photography. Ex vivo retinal testing included Periodic acid Schiff Diastase (PASD) staining, followed by imaging to assess and quantify LB deposition. There was no significant difference in any dark-adapted or light-adapted ERG parameters between KO and WT mice. The total retinal thickness was cFigure mparable between the groups and the retinal appearance was normal in both groups. On PASD staining, LBs were observed in KO mice within the inner and outer plexiform layers and in the inner nuclear layer. The average number of LBs within the inner plexiform layer in KO mice were 1743 ± 533 and 2615 ± 915 per mm2, at 10 and 14 months, respectively. This is the first study to characterize the retinal phenotype in an Epm2a−/− mouse model, demonstrating significant LB deposition in the bipolar cell nuclear layer and its synapses. This finding may be used to monitor the efficacy of experimental treatments in mouse models.

OCT and ERG Techniques in High-Throughput Phenotyping of Mouse Vision

The purpose of the study is to demonstrate coherent optical tomography and electroretinography techniques adopted from the human clinical practice to assess the morphology and function of the mouse retina in a high-throughput phenotyping environment. We present the normal range of wild-type C57Bl/6NCrl retinal parameters in six age groups between 10 and 100 weeks as well as examples of mild and severe pathologies resulting from knocking out a single protein-coding gene. We also show example data obtained by more detailed analysis or additional methods useful in eye research, for example, the angiography of a superficial and deep vascular complex. We discuss the feasibility of these techniques in conditions demanding a high-throughput approach such as the systemic phenotyping carried out by the International Mouse Phenotyping Consortium.

Deep phenotyping and lifetime trajectories reveal limited effects of longevity regulators on the aging process in C57BL/6J mice

Current concepts regarding the biology of aging are primarily based on studies aimed at identifying factors regulating lifespan. However, lifespan as a sole proxy measure for aging can be of limited value because it may be restricted by specific pathologies. Here, we employ large-scale phenotyping to analyze hundreds of markers in aging male C57BL/6J mice. For each phenotype, we establish lifetime profiles to determine when age-dependent change is first detectable relative to the young adult baseline. We examine key lifespan regulators (putative anti-aging interventions; PAAIs) for a possible countering of aging. Importantly, unlike most previous studies, we include in our study design young treated groups of animals, subjected to PAAIs prior to the onset of detectable age-dependent phenotypic change. Many PAAI effects influence phenotypes long before the onset of detectable age-dependent change, but, importantly, do not alter the rate of phenotypic change. Hence, these PAAIs have limited effects on aging.

Progressive retinal degeneration of rods and cones in a Bardet-Biedl syndrome type 10 mouse model

Bardet-Biedl syndrome (BBS) is a multi-organ autosomal-recessive disorder caused by mutations in at least 22 different genes. A constant feature is early-onset retinal degeneration leading to blindness. Among the most common forms is BBS type 10 (BBS10), which is caused by mutations in a gene encoding a chaperonin-like protein. To aid in developing treatments, we phenotyped a Bbs10 knockout (Bbs10-/-) mouse model. Analysis by optical coherence tomography (OCT), electroretinography (ERG) and a visually guided swim assay (VGSA) revealed a progressive degeneration (from P19 to 8 months of age) of the outer nuclear layer that is visible by OCT and histology. Cone ERG was absent from at least P30, at which time rod ERG was reduced to 74.4% of control levels; at 8 months, rod ERG was 2.3% of that of controls. VGSA demonstrated loss of functional vision at 9 months. These phenotypes progressed more rapidly than retinal degeneration in the Bbs1M390R/M390R knock-in mouse. This study defines endpoints for preclinical trials that can be utilized to detect a treatment effect in the Bbs10-/- mouse and extrapolated to human clinical trials.

Sodium butyrate-loaded nanoparticles coated with chitosan for the treatment of neovascularization in age-related macular degeneration: ocular biocompatibility and antiangiogenic activity

Sodium butyrate-loaded nanoparticles coated chitosan (NaBu-loaded nanoparticles/CS) were developed to treat the choroidal neovascularization in wet age-related macular degeneration (AMD). The nanoparticles were produced by double emulsification and solvent evaporation technique, optimized by experimental statistical design, characterized by analytical methods, investigated in terms of in vitro and in vivo ocular biocompatibility, and evaluated as an antiangiogenic system in vivo. The NaBu-loaded nanoparticles/CS were 311.1 ± 3.1 nm in diameter with a 0.208 ± 0.007 polydispersity index; had a +56.3 ± 2.6 mV zeta potential; showed a 92.3% NaBu encapsulation efficiency; and sustained the drug release over 35 days. The NaBu-loaded nanoparticles/CS showed no toxicity to human retinal pigment epithelium cells (ARPE-19 cells); was not irritant to the chorioallantoic membrane (CAM); did not interfere in the integrity of the retinal layers of rat's eyes, as detected by the Optical Coherence Tomography and histopathology; and inhibited the angiogenesis in CAM assay. The NaBu-loaded nanoparticles/CS could be a therapeutic alternative to limit the neovascularization in AMD.

Subcellular Comparison of Visible-Light Optical Coherence Tomography and Electron Microscopy in the Mouse Outer Retina

Purpose

We employed in vivo, 1.0-µm axial resolution visible-light optical coherence tomography (OCT) and ex vivo electron microscopy (EM) to investigate three subcellular features in the mouse outer retina: reflectivity oscillations inner to band 1 (study 1); hyperreflective band 2, attributed to the ellipsoid zone or inner segment/outer segment (IS/OS) junction (study 2); and the hyperreflective retinal pigment epithelium (RPE) within band 4 (study 3).

Methods

Pigmented (C57BL/6J, n = 10) and albino (BALB/cJ, n = 3) mice were imaged in vivo. Enucleated eyes were processed for light and electron microscopy. Using well-accepted reference surfaces, we compared micrometer-scale axial reflectivity of visible-light OCT with subcellular organization, as revealed by 9449 annotated EM organelles and features across four pigmented eyes.

Results

In study 1, outer nuclear layer reflectivity peaks coincided with valleys in heterochromatin clump density (-0.34 ± 2.27 µm limits of agreement [LoA]). In study 2, band 2 depth on OCT and IS/OS junction depth on EM agreed (-0.57 ± 0.76 µm LoA), with both having similar distributions. In study 3, RPE electron dense organelle distribution did not agree with reflectivity in C57BL/6J mice, with OCT measures of RPE thickness exceeding those of EM (2.09 ± 0.89 µm LoA). Finally, RPE thickness increased with age in pigmented mice (slope = 0.056 µm/mo; P = 6.8 × 10-7).

Conclusions

Visible-light OCT bands arise from subcellular organization, enabling new measurements in mice. Quantitative OCT-EM comparisons may be confounded by hydration level, particularly in the OS and RPE. Caution is warranted in generalizing results to other species.

Mural Cell SRF Controls Pericyte Migration, Vessel Patterning and Blood Flow

Pericytes and vascular smooth muscle cells, collectively known as mural cells, are recruited through PDGFB (platelet-derived growth factor B)-PDGFRB (platelet-derived growth factor receptor beta) signaling. MCs are essential for vascular integrity, and their loss has been associated with numerous diseases. Most of this knowledge is based on studies in which MCs are insufficiently recruited or fully absent upon inducible ablation. In contrast, little is known about the physiological consequences that result from impairment of specific MC functions. Here, we characterize the role of the transcription factor SRF (serum response factor) in MCs and study its function in developmental and pathological contexts.

Sodium-Iodate Injection Can Replicate Retinal Degenerative Disease Stages in Pigmented Mice and Rats: Non-Invasive Follow-Up Using OCT and ERG

Purpose: The lack of suitable animal models for (dry) age-related macular degeneration (AMD) has hampered therapeutic research into the disease, so far. In this study, pigmented rats and mice were systematically injected with various doses of sodium iodate (SI). After injection, the retinal structure and visual function were non-invasively characterized over time to obtain in-depth data on the suitability of these models for studying experimental therapies for retinal degenerative diseases, such as dry AMD. Methods: SI was injected into the tail vein (i.v.) using a series of doses (0–70 mg/kg) in adolescent C57BL/6J mice and Brown Norway rats. The retinal structure and function were assessed non-invasively at baseline (day 1) and at several time points (1–3, 5, and 10-weeks) post-injection by scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and electroretinography (ERG). Results: After the SI injection, retinal degeneration in mice and rats yielded similar results. The lowest dose (10 mg/kg) resulted in non-detectable structural or functional effects. An injection with 20 mg/kg SI did not result in an evident retinal degeneration as judged from the OCT data. In contrast, the ERG responses were temporarily decreased but returned to baseline within two-weeks. Higher doses (30, 40, 50, and 70 mg/kg) resulted in moderate to severe structural RPE and retinal injury and decreased the ERG amplitudes, indicating visual impairment in both mice and rat strains. Conclusions: After the SI injections, we observed dose-dependent structural and functional pathological effects on the retinal pigment epithelium (RPE) and retina in the pigmented mouse and rat strains that were used in this study. Similar effects were observed in both species. In particular, a dose of 30 mg/kg seems to be suitable for future studies on developing experimental therapies. These relatively easily induced non-inherited models may serve as useful tools for evaluating novel therapies for RPE-related retinal degenerations, such as AMD.

A Splicing Mutation in Slc4a5 Results in Retinal Detachment and Retinal Pigment Epithelium Dysfunction

Fluid and solute transporters of the retinal pigment epithelium (RPE) are core components of the outer blood-retinal barrier. Characterizing these transporters and their role in retinal homeostasis may provide insights into ocular function and disease. Here, we describe RPE defects in tvrm77 mice, which exhibit hypopigmented patches in the central retina. Mapping and nucleotide sequencing of tvrm77 mice revealed a disrupted 5' splice donor sequence in Slc4a5, a sodium bicarbonate cotransporter gene. Slc4a5 expression was reduced 19.7-fold in tvrm77 RPE relative to controls, and alternative splice variants were detected. SLC4A5 was localized to the Golgi apparatus of cultured human RPE cells and in apical and basal membranes. Fundus imaging, optical coherence tomography, microscopy, and electroretinography (ERG) of tvrm77 mice revealed retinal detachment, hypopigmented patches corresponding to neovascular lesions, and retinal folds. Detachment worsened and outer nuclear layer thickness decreased with age. ERG a- and b-wave response amplitudes were initially normal but declined in older mice. The direct current ERG fast oscillation and light peak were reduced in amplitude at all ages, whereas other RPE-associated responses were unaffected. These results link a new Slc4a5 mutation to subretinal fluid accumulation and altered light-evoked RPE electrophysiological responses, suggesting that SLC4A5 functions at the outer blood-retinal barrier.

Volumetric directional optical coherence tomography

Photoreceptor loss and resultant thinning of the outer nuclear layer (ONL) is an important pathological feature of retinal degenerations and may serve as a useful imaging biomarker for age-related macular degeneration. However, the demarcation between the ONL and the adjacent Henle's fiber layer (HFL) is difficult to visualize with standard optical coherence tomography (OCT). A dedicated OCT system that can precisely control and continuously and synchronously update the imaging beam entry points during scanning has not been realized yet. In this paper, we introduce a novel imaging technology, Volumetric Directional OCT (VD-OCT), which can dynamically adjust the incident beam on the pupil without manual adjustment during a volumetric OCT scan. We also implement a customized spoke-circular scanning pattern to observe the appearance of HFL with sufficient optical contrast in continuous cross-sectional scans through the entire volume. The application of VD-OCT for retinal imaging to exploit directional reflectivity properties of tissue layers has the potential to allow for early identification of retinal diseases.

Morphometric and Microstructural Changes During Murine Retinal Development Characterized Using In Vivo Optical Coherence Tomography

Purpose

The purpose of this study was to develop an in vivo optical coherence tomography (OCT) system capable of imaging the developing mouse retina and its associated morphometric and microstructural changes.

Methods

Thirty-four wild-type mice (129S1/SvlmJ) were anesthetized and imaged between postnatal (P) day 7 and P21. OCT instrumentation was developed to optimize signal intensity and image quality. Semi-automatic segmentation tools were developed to quantify the retinal thickness of the nerve fiber layer (NFL), inner plexiform layer (IPL), inner nuclear layer (INL), and the outer retinal layers (ORL), in addition to the total retina. The retinal maturation was characterized by comparing layer thicknesses between consecutive time points.

Results

From P7 to P10, the IPL increased significantly, consistent with retinal synaptogenesis. From P10 to P12, the IPL and ORL also increased, which is coherent with synaptic connectivity and photoreceptor maturation. In contrast, during these periods, the INL decreased significantly, consistent with cellular densification and selective apoptotic “pruning” of the tissue during nuclear migration. Thereafter from P12 to P21, the INL continued to thin (significantly from P17 to P21) whereas the other layers remained unchanged. No time-dependent changes were observed in the NFL. Overall, changes in the total retina were attributed to those in the IPL, INL, and ORL. Regions of the retina adjacent to the optic nerve head were thinner than distal regions during maturation.

Conclusions

Changes in retinal layer thickness are consistent with retinal developmental mechanisms. Accordingly, this report opens new horizons in using our system in the mouse to characterize longitudinally developmental digressions in models of human diseases.

In vivo imaging of the inner retinal layer structure in mice after eye-opening using visible-light optical coherence tomography

The growth of the mouse eye and retina after birth is a dynamic, highly regulated process. In this study, we applied visible-light optical coherence tomography (vis-OCT), a non-invasive imaging technique, to examine developing retinal layer structures after eye-opening. We introduced a resampled circumpapillary B-scan averaging technique to improve the inter-layer contrast, enabling retinal layer thickness measurements as early as postnatal day 13 (P13) - right after eye-opening. We confirmed vis-OCT measurements using ex vivo confocal microscopy of retinal sections at different ages. Our results demonstrate that vis-OCT can visualize the developmental murine retinal layer structure in vivo, which offers us new opportunities to better characterize the pathological alterations in mouse models of developmental eye diseases.

The TGFβ/Notch axis facilitates Müller cell-to-epithelial transition to ultimately form a chronic glial scar

Background

Contrasting with zebrafish, retinal regeneration from Müller cells (MCs) is largely limited in mammals, where they undergo reactive gliosis that consist of a hypertrophic response and ultimately results in vision loss. Transforming growth factor β (TGFβ) is essential for wound healing, including both scar formation and regeneration. However, targeting TGFβ may affect other physiological mechanisms, owing its pleiotropic nature. The regulation of various cellular activities by TGFβ relies on its interaction with other pathways including Notch. Here, we explore the interplay of TGFβ with Notch and how this regulates MC response to injury in zebrafish and mice. Furthermore, we aimed to characterize potential similarities between murine and human MCs during chronic reactive gliosis.

Methods

Focal damage to photoreceptors was induced with a 532 nm diode laser in TgBAC (gfap:gfap-GFP) zebrafish (ZF) and B6-Tg (Rlbp1-GFP) mice. Transcriptomics, immunofluorescence, and flow cytometry were employed for a comparative analysis of MC response to laser-induced injury between ZF and mouse. The laser-induced injury was paired with pharmacological treatments to inhibit either Notch (DAPT) or TGFβ (Pirfenidone) or TGFβ/Notch interplay (SIS3). To determine if the murine laser-induced injury model translates to the human system, we compared the ensuing MC response to human donors with early retinal degeneration.

Results

Investigations into injury-induced changes in murine MCs revealed TGFβ/Notch interplay during reactive gliosis. We found that TGFβ1/2 and Notch1/2 interact via Smad3 to reprogram murine MCs towards an epithelial lineage and ultimately to form a glial scar. Similar to what we observed in mice, we confirmed the epithelial phenotype of human Müller cells during gliotic response.

Conclusion

The study indicates a pivotal role for TGFβ/Notch interplay in tuning MC stemness during injury response and provides novel insights into the remodeling mechanism during retinal degenerative diseases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00482-z.

Quantitative Assessment of Experimental Ocular Inflammatory Disease

Ocular inflammation imposes a high medical burden on patients and substantial costs on the health-care systems that mange these often chronic and debilitating diseases. Many clinical phenotypes are recognized and classifying the severity of inflammation in an eye with uveitis is an ongoing challenge. With the widespread application of optical coherence tomography in the clinic has come the impetus for more robust methods to compare disease between different patients and different treatment centers. Models can recapitulate many of the features seen in the clinic, but until recently the quality of imaging available has lagged that applied in humans. In the model experimental autoimmune uveitis (EAU), we highlight three linked clinical states that produce retinal vulnerability to inflammation, all different from healthy tissue, but distinct from each other. Deploying longitudinal, multimodal imaging approaches can be coupled to analysis in the tissue of changes in architecture, cell content and function. This can enrich our understanding of pathology, increase the sensitivity with which the impacts of therapeutic interventions are assessed and address questions of tissue regeneration and repair. Modern image processing, including the application of artificial intelligence, in the context of such models of disease can lay a foundation for new approaches to monitoring tissue health.

Non-invasive multimodal imaging of Diabetic Retinopathy: A survey on treatment methods and Nanotheranostics

Diabetes Retinopathy (DR) is one of the most prominent microvascular complications of diabetes. It is one of the pre-eminent causes for vision impairment followed by blindness among the working-age population worldwide. The de facto cause for DR remains challenging, despite several efforts made to unveil the mechanism underlying the pathology of DR. There is quite less availability of the low cost pre-emptive theranostic imaging tools in terms of in-depth resolution, due to the multiple factors involved in the etiology of DR. This review work comprehensively explores the various reports and research works on all perspectives of diabetic retinopathy (DR), and its mechanism. It also discusses various advanced non-destructive imaging modalities, current, and future treatment approaches. Further, the application of various nanoparticle-based drug delivery strategies used for the treatment of DR are also discussed. In a nutshell, the present review work bolsters the pursuit of the development of an advanced non-invasive optical imaging modal with a nano-theranostic approach for the future diagnosis and treatment of DR and its associated ocular complications.

Multi-layer Shack-Hartmann wavefront sensing in the point source regime

The Shack-Hartmann wavefront sensor (SHWS) is often operated under the assumption that the sensed light can be described by a single wavefront. In biological tissues and other multi-layered samples, secondary wavefronts from axially and/or transversely displaced regions can lead to artifactual aberrations. Here, we evaluate these artifactual aberrations in a simulated ophthalmic SHWS by modeling the beacons that would be generated by a two-layer retina in human and mouse eyes. Then, we propose formulae for calculating a minimum SHWS centroid integration area to mitigate these aberrations by an order of magnitude, potentially benefiting SHWS-based metrology and adaptive optics systems such as those used for retinal imaging and microscopy.

Increased episcleral venous pressure in a mouse model of circumlimbal suture induced ocular hypertension

PURPOSE

To investigate changes in aqueous humor dynamics during intraocular pressure (IOP) elevation induced by circumlimbal suture in mice.

METHODS

Ocular hypertension (OHT) was induced by applying a circumlimbal suture behind the limbus in male adult C57BL6/J mice. In the OHT group, the suture was left in place for an average of 8 weeks (n = 10, OHT group). In the sham control group the suture was cut at 2 days (n = 9, sham group) and in the naïve control group (n = 5) no suture was implanted. IOP was measured at baseline across 3 days, 1 h post-suture implantation, and at the chronic endpoint. Anterior segments were assessed using optical coherence tomography (OCT). Episcleral venous pressure (EVP), total outflow facility (C), uveoscleral outflow (Fu) and aqueous humor flow rate (Fin) were determined using a constant-flow infusion model.

RESULTS

All aqueous dynamic and chronic IOP outcome measures showed no difference between sham and naïve controls (p > 0.05) and thus these groups were combined into a single control group. IOP was elevated in OHT group compared with controls (p < 0.01). Chronic suture implantation did not change pupil size, anterior chamber depth or iridocorneal angles (p > 0.05). EVP was significantly higher in OHT eyes compared to control eyes (p < 0.01). There was no statistical difference in C, Fu and Fin between groups (p > 0.05). A significant linear correlation was found between IOP and EVP (R² = 0.35, p = 0.001).

CONCLUSIONS

Circumlimbal suture implantation in mouse eyes results in chronic IOP elevation without angle closure. Chronic IOP elevation is likely to reflect higher EVP.

In vivo retinal imaging in translational regenerative research

Regenerative translational studies must include a longitudinal assessment of the changes in retinal structure and function that occur as part of the natural history of the disease and those that result from the studied intervention. Traditionally, retinal structural changes have been evaluated by histological analysis which necessitates sacrificing the animals. In this review, we describe key imaging approaches such as fundus imaging, optical coherence tomography (OCT), OCT-angiography, adaptive optics (AO), and confocal scanning laser ophthalmoscopy (cSLO) that enable noninvasive, non-contact, and fast in vivo imaging of the posterior segment. These imaging technologies substantially reduce the number of animals needed and enable progression analysis and longitudinal follow-up in individual animals for accurate assessment of disease natural history, effects of interventions and acute changes. We also describe the benefits and limitations of each technology, as well as outline possible future directions that can be taken in translational retinal imaging studies.

Noninvasive Imaging of Cone Ablation and Regeneration in Zebrafish

Purpose

To observe and characterize cone degeneration and regeneration in a selective metronidazole-mediated ablation model of ultraviolet-sensitive (UV) cones in zebrafish using in vivo optical coherence tomography (OCT) imaging.

Methods

Twenty-six sws1:nfsB-mCherry;sws2:eGFP zebrafish were imaged with OCT, treated with metronidazole to selectively kill UV cones, and imaged at 1, 3, 7, 14, 28, or 56 days after ablation. Regions 200 × 200 µm were cropped from volume OCT scans to count individual UV cones before and after ablation. Fish eyes were fixed, and immunofluorescence staining was used to corroborate cone density measured from OCT and to track monocyte response.

Results

Histology shows significant loss of UV cones after metronidazole treatment with a slight increase in observable blue cone density one day after treatment (Kruskal, Wallis, P = 0.0061) and no significant change in blue cones at all other timepoints. Regenerated UV cones measured from OCT show significantly lower density than pre-cone-ablation at 14, 28, and 56 days after ablation (analysis of variance, P < 0.01, P < 0.0001, P < 0.0001, respectively, 15.9% of expected nonablated levels). Histology shows significant changes to monocyte morphology (mixed-effects analysis, P < 0.0001) and retinal position (mixed-effects analysis, P < 0.0001).

Conclusions

OCT can be used to observe loss of individual cones selectively ablated by metronidazole prodrug activation and to quantify UV cone loss and regeneration in zebrafish. OCT images also show transient changes to the blue cone mosaic and inner retinal layers that occur concomitantly with selective UV cone ablation.

Translational Relevance

Profiling cone degeneration and regeneration using in vivo imaging enables experiments that may lead to a better understanding of cone regeneration in vertebrates.

An anchoring molecule increases intravitreal retention of antibody-based therapeutics used in the treatment of ocular diseases

Intravitreal delivery of antibody-based therapeutics has revolutionized the treatment of intraocular vascular diseases involving the retina and choroid. Unfortunately, limited durability requires frequent retreatment placing an enormous burden on patients. We sought to solve this problem with a novel approach that uses an anchoring molecule characterized by two key molecular properties: (1) non-covalent binding to an antibody-based therapeutic, and (2) retention in the vitreous cavity. As an initial proof-of-principle, we chose an anchoring molecule composed of agarose microbeads functionalized with an Fc-binding domain. Bevacizumab was chosen as the antibody-based therapeutic. In vitro experiments demonstrated that bevacizumab was maximally bound to this anchoring molecule within 1 h, and was competitively released upon exposure to either polyclonal human (p < 0.0001) or rat (p = 0.0017) immunoglobulins. In silico modeling predicted prolonged intravitreal retention of an antibody-based therapeutic in the presence of this anchoring molecule, which was confirmed by in vivo experiments with this initial anchoring molecule in rats. This anchoring molecule increased the intraocular half-life of bevacizumab from 5.8 days to over 18 days and maintained therapeutic concentrations for over 80 days. Despite showing no evidence of direct cellular toxicity, this anchoring molecule collected in the anterior vitreous, partially obscuring retinal visualization and eliciting a mild chronic microglial/macrophage inflammatory response. These studies provide a plausible approach to the development of novel non-covalent methods of binding, retention, and release of antibody-based therapeutics in the vitreous.

A new rat model of treatment-naive quiescent choroidal neovascularization induced by human VEGF165 overexpression

Vascular endothelial growth factor (VEGF) is a crucial stimulator for choroidal neovascularization (CNV). Our aim was to develop a reproducible and valid treatment-naive quiescent CNV (i.e. without signs of exudation and with normal visual acuity) rat model by subretinal injection of an adeno-associated virus (AAV)-VEGFA165 vector. The CNV development was longitudinally followed up in vivo by scanning laser ophthalmoscopy/optical coherence tomography, fluorescein and Indocyanine Green angiographies and ex vivo by electron microscopy (EM) and immunohistochemistry. In total, 57 eyes were analysed. In vivo, a quiescent CNV was observed in 93% of the eyes 6 weeks post-transduction. In EM, CNV vessels with few fenestrations, multi-layered basement membranes and bifurcation of endothelial cells were observed sharing the human CNV features. Human VEGF overexpression, multi-layered retinal pigment epithelium (RPE) (RPE65) and macrophages/activated microglia (Iba1) were also detected. In addition, 19 CNV eyes were treated for up to 3 weeks with bevacizumab. The retinal and CNV lesion thickness decreased significantly in bevacizumab-treated CNV eyes compared with untreated CNV eyes 1 week after the treatment. In conclusion, our experimental CNV resembles those seen in patients suffering from treatment-naive quiescent CNV in wet age-related macular degeneration (AMD), and responds to short-term treatment with bevacizumab. Our new model can, therefore, be used to test the long-term effect of new drugs targeting CNV under precisely-defined conditions.

Measurement of Diurnal Variation in Rod Outer Segment Length In Vivo in Mice With the OCT Optoretinogram

Purpose

To investigate diurnal variation in the length of mouse rod outer segments in vivo.

Methods

The lengths of rod inner and outer segments (RIS, ROS) of dark-adapted albino mice maintained on a 12-hour dark:12-hour light cycle with light onset 7 AM were measured at prescribed times (6:30 AM, 11 AM, 3:30 PM) during the diurnal cycle with optical coherence tomography (OCT), taking advantage of increased visibility, after a brief bleaching exposure, of the bands corresponding to RIS/ROS boundaries and ROS tips (ROST).

Results

Deconvolution of OCT depth profiles resolved two backscatter bands located 7.4 ± 0.1 and 10.8 ± 0.2 µm (mean ± SEM) proximal to Bruch's membrane (BrM). These bands were identified with histology as arising from the apical surface of RPE and ROST, respectively. The average length of dark-adapted ROS at 6:30 AM was 17.7 ± 0.8 µm. By 11 AM, the average ROS length had decreased by 10% to 15.9 ± 0.7 µm. After 11 AM, the ROS length increased steadily at an average rate of 0.12 µm/h, returning to baseline length by 23.5 hours in the cycle.

Conclusions

The diurnal variation in ROS length measured in these experiments is consistent with prior histological investigations showing that rodent rod discs are phagocytosed by the RPE maximally over several hours around the time of normal light onset. The rate of recovery of ROS to baseline length before normal light onset is consistent with the hypothesis that disc membrane synthesis is fairly constant over the diurnal cycle.

Assessing the anterior visual pathway in optic neuritis: recent experimental and clinical aspects

PURPOSE OF REVIEW

Multiple sclerosis (MS) and related autoimmune disorders of the central nervous system such as neuromyelitis optica spectrum disorders (NMOSD) are characterized by chronic disability resulting from autoimmune neuroinflammation, with demyelination, astrocyte damage, impaired axonal transmission and neuroaxonal loss. Novel therapeutics stopping or reversing the progression of disability are still urgently warranted. This review addresses research on optic neuritis in preclinical experimental models and their translation to clinical trials.

RECENT FINDINGS

Optic neuritis can be used as paradigm for an MS relapse which can serve to evaluate the efficacy of novel therapeutics in clinical trials with a reasonable duration and cohort size. The advantage is the linear structure of the visual pathway allowing the assessment of visual function and retinal structure as highly sensitive outcome parameters. Experimental autoimmune encephalomyelitis is an inducible, inflammatory and demyelinating central nervous system disease extensively used as animal model of MS. Optic neuritis is part of the clinicopathological manifestations in a number of experimental autoimmune encephalomyelitis models. These have gained increasing interest for studies evaluating neuroprotective and/or remyelinating substances as longitudinal, visual and retinal readouts have become available.

SUMMARY

Translation of preclinical experiments, evaluating neuroprotective or remyelinating therapeutics to clinical studies is challenging. In-vivo readouts like optical coherence tomography, offers the possibility to transfer experimental study designs to clinical optic neuritis trials.

Interpretation of OCT and OCTA images from a histological approach: Clinical and experimental implications

Optical coherence tomography (OCT) and OCT angiography (OCTA) have been a technological breakthrough in the diagnosis, treatment, and follow-up of many retinal diseases, thanks to its resolution and its ability to inform of the retinal state in seconds, which gives relevant information about retinal degeneration. In this review, we present an immunohistochemical description of the human and mice retina and we correlate it with the OCT bands in health and pathological conditions. Here, we propose an interpretation of the four outer hyperreflective OCT bands with a correspondence to retinal histology: the first and innermost band as the external limiting membrane (ELM), the second band as the cone ellipsoid zone (EZ), the third band as the outer segment tips phagocytosed by the pigment epithelium (PhaZ), and the fourth band as the mitochondria in the basal portion of the RPE (RPEmitZ). The integrity of these bands would reflect the health of photoreceptors and retinal pigment epithelium. Moreover, we describe how the vascular plexuses vary in different regions of the healthy human and mice retina, using OCTA and immunohistochemistry. In humans, four, three, two or one plexuses can be observed depending on the distance from the fovea. Also, specific structures such as vascular loops in the intermediate capillary plexus, or spider-like structures of interconnected capillaries in the deep capillary plexus are found. In mice, three vascular plexuses occupy the whole retina, except in the most peripheral retina where only two plexuses are found. These morphological issues should be considered when assessing a pathology, as some retinal diseases are associated with structural changes in blood vessels. Therefore, the analysis of OCT bands and OCTA vascular plexuses may be complementary for the diagnosis and prognosis of retinal degenerative processes, useful to assess therapeutic approaches, and it is usually correlated to visual acuity.

Monitoring retinal changes with optical coherence tomography predicts neuronal loss in experimental autoimmune encephalomyelitis

Background

Retinal optical coherence tomography (OCT) is a clinical and research tool in multiple sclerosis, where it has shown significant retinal nerve fiber (RNFL) and ganglion cell (RGC) layer thinning, while postmortem studies have reported RGC loss. Although retinal pathology in experimental autoimmune encephalomyelitis (EAE) has been described, comparative OCT studies among EAE models are scarce. Furthermore, the best practices for the implementation of OCT in the EAE lab, especially with afoveate animals like rodents, remain undefined. We aimed to describe the dynamics of retinal injury in different mouse EAE models and outline the optimal experimental conditions, scan protocols, and analysis methods, comparing these to histology to confirm the pathological underpinnings.

Methods

Using spectral-domain OCT, we analyzed the test-retest and the inter-rater reliability of volume, peripapillary, and combined horizontal and vertical line scans. We then monitored the thickness of the retinal layers in different EAE models: in wild-type (WT) C57Bl/6J mice immunized with myelin oligodendrocyte glycoprotein peptide (MOG_35–55) or with bovine myelin basic protein (MBP), in TCR^2D2 mice immunized with MOG_35–55, and in SJL/J mice immunized with myelin proteolipid lipoprotein (PLP_139–151). Strain-matched control mice were sham-immunized. RGC density was counted on retinal flatmounts at the end of each experiment.

Results

Volume scans centered on the optic disc showed the best reliability. Retinal changes during EAE were localized in the inner retinal layers (IRLs, the combination of the RNFL and the ganglion cell plus the inner plexiform layers). In WT, MOG_35–55 EAE, progressive thinning of IRL started rapidly after EAE onset, with 1/3 of total loss occurring during the initial 2 months. IRL thinning was associated with the degree of RGC loss and the severity of EAE. Sham-immunized SJL/J mice showed progressive IRL atrophy, which was accentuated in PLP-immunized mice. MOG_35–55-immunized TCR^2D2 mice showed severe EAE and retinal thinning. MBP immunization led to very mild disease without significant retinopathy.

Conclusions

Retinal neuroaxonal damage develops quickly during EAE. Changes in retinal thickness mirror neuronal loss and clinical severity. Monitoring of the IRL thickness after immunization against MOG_35–55 in C57Bl/6J mice seems the most convenient model to study retinal neurodegeneration in EAE.

Macular thickness measurements of healthy, naïve cynomolgus monkeys assessed with spectral-domain optical coherence tomography (SD-OCT)

The purpose of this study was to measure central macular thickness in an unprecedented number of cynomolgus monkeys. Macular thickness was measured with Heidelberg spectral-domain OCT in 320 eyes of healthy and treatment-naïve cynomolgus monkeys (80 males and 80 females). The macula was successfully measured in all 320 eyes. Macular thickness was not significantly different between the sexes. The mean central macular thickness was 244 μm (+/- 21 μm). Macular thicknesses in the quadrants were 327 +/-17 μm (temporal inner), 339 +/- 17 μm (inferior inner), 341 +/- 14 μm (superior inner), 341 +/-18 μm (nasal inner), and 299 +/- 20 μm (temporal outer), 320 +/- 16 μm (superior outer), 332 +/-23 μm (inferior outer), and 337 +/-18 μm (nasal outer). Highly significant differences between the nasal and temporal quadrants were detected. This study successfully demonstrated the feasibility of retinal thickness measurements in healthy cynomolgus monkeys. The present findings indicate that the macula is thicker in cynomolgus monkeys than in humans and provide important normative data for future studies.

Development and optimisation of an animal model for the study of ganglion cells in degenerative diseases of the retina and optic nerve

INTRODUCTION

Multiple sclerosis is an autoimmune, chronic and inflammatory disease of the central nervous system with axonal demyelination, gliosis and neurodegeneration. It is considered a frequent cause of neurological disability in young adults. In this work, an Experimental Autoimmune Encephalomyelitis (EAE) model was optimised by injecting a myelin oligodendrocyte glycoprotein (MOG_35-55). The ophthalmological effects were studied, as well as its use as an experimental model in other studies of retinal ganglion cell degeneration (RGC) and optic nerve (ON).

MATERIAL AND METHODS

The study included 16 mice of 10 weeks that were placed into 2 study groups: a control group of 10 animals and another group of 6 animals with EAE that were injected with MOG_35-55. The animals of the EAE model were monitored using motor disability scales. The retinas and optic nerves were processed for morphological examination by optical microscopy and ultrastructure studies.

RESULTS

The animal models presented with motor symptoms of spinal cord injury, with the first symptoms appearing between the 7th and 19th day post-injection, with a maximum disability mean of 3.5 points. In the retina, the mean RGC in the EAE group was 0.0891μm, compared with 0.1678μm of the control group (p=.0003). The ON was strongly affected with reactive gliosis, increased axonal damage and decreased density axonal (control group 0.38038 axons/μm² versus EAE group 0.16 axons/μm², p=.00032).

CONCLUSIONS

In this work an animal model of EAE has been characterised and detailed for the study of demyelinating alterations in the retina and the ON. Its characteristics make it an excellent tool for the study of neurodegenerative ophthalmic diseases.

A retinal model of cerebral malaria

Malaria is a causative factor in about 500.000 deaths each year world-wide. Cerebral malaria is a particularly severe complication of this disease and thus associated with an exceedingly high mortality. Malaria retinopathy is an ocular manifestation often associated with cerebral malaria, and presumably shares a substantial part of its pathophysiology. Here, we describe that indeed murine malaria retinopathy reproduced the main hallmarks of the corresponding human disease. In the living animal, we were able to follow the circulation and cellular localization of malaria parasites transgenically labelled with GFP via non-invasive in vivo retinal imaging. We found that malaria parasites cross the blood-retinal-barrier and infiltrate the neuroretina, concomitant with an extensive, irreversible, and long-lasting retinal neurodegeneration. Furthermore, anti-malarial treatment with dihydroartemisinin strongly diminished the load of circulating parasites but resolved the symptoms of the retinopathy only in part. In summary, we introduce here a novel preclinical model for human cerebral malaria that is much more directly accessible for studies into disease pathophysiology and development of novel treatment approaches. In vivo retinal imaging may furthermore serve as a valuable tool for the early diagnosis of the human disease.

A Population Study of Common Ocular Abnormalities in C57BL/6N rd8 Mice

Purpose

The purpose of this study was to quantify the frequency and severity of ocular abnormalities affecting wild-type C57BL/6N mice, the most common strain used worldwide for the creation of single-gene knockouts.

Methods

A total of 2773 animals (5546 eyes) were examined at one colony at UC Davis and in three more colonies at the Institut Clinique de la Souris in Strasbourg, France. Mice were examined at 15 to 16 weeks postnatal age by performing anterior segment biomicroscopy, posterior segment examination by indirect ophthalmoscopy, intraocular pressure measurement, and optical coherence tomography of anterior and posterior segment structures.

Results

Common ocular findings in the C57BL/6N strain included corneal deposits (3%), increased optical density of the anterior lens capsule (67%), punctate nuclear cataracts (98%), vitreous crystalline deposits (61%), hyaloid vascular remnant (6%), and retinal dysplasia attributed to the rd8 mutation (58%). Interestingly, retinal dysplasia was more common in male mice in all four breeding colonies evaluated in this study. The thickness of ocular tissues and compartments were measured by spectral-domain optical coherence tomography, including the central cornea, anterior chamber, vitreous, and retinal layers. Intraocular pressure was measured by rebound tonometry.

Conclusions

Ocular abnormalities are common in anterior and posterior segments of the C57BL/6N mouse, the most common background on which single-gene knockout mice have been made. It is important that vision scientists understand the extent and variability of ocular findings associated with this particular genetic background of mice.

Phenotyping of Mouse Models with OCT

Optical coherence tomography (OCT) is an invaluable technique to perform noninvasive retinal imaging in small animal models such as mice. It provides virtual cross sections that correlate well with histomorphometric data with the advantage that multiple iterative measurements can be acquired in timeline analyses to detect dynamic changes and reduce the number of animals needed per study.

Optic nerve head width and retinal nerve fiber layer changes are proper indexes for validating the successful induction of experimental anterior ischemic optic neuropathy

Reproducible skills are essential for successful induction of a rat model of anterior ischemic optic neuropathy (rAION). We established an in vivo validation index by measuring the natural course of optic nerve head (ONH) width and retinal nerve fiber layer (RNFL) thickness in the rAION model using optical coherence tomography (OCT). The rAION model was induced by photodynamic operations. We measured the ONH width, RNFL, Inner Plexiform layer (IPL) and Ganglion cell complex (GCC) thickness in the acute stage (<3 days), subacute stage (day-7 to day-14) and later stage (day-14 to day-28) post-infarct by OCT. Retinal layers were measured by hematoxylin and eosin stain (HE) to confirm the OCT findings. The RGCs survival rate was determined by retrograde Fluoro-gold labeling, and the visual function was assessed with flash visual-evoked potentials (FVEPs) 4 weeks post-infarct. We observed significant thinning in GCC, IPL, and RNFL at day-14 and day-28 but only RNFL showed significant thinning between day-14 and day-28. The ONH showed significant swelling in the acute stage which correlated at a greater extent with RNFL than GCC and IPL. Further RNFL correlated at a greater extent at with GCC than IPL. HE-stained retina cross sections also showed IPL and RNFL thinning, which further confirmed our OCT findings. The RGC density and P1-N2 amplitude were significantly reduced in rAION. Our data suggest that Swelling, reduction of swelling, and atrophy of RNFL in acute, sub-acute, and later stage, respectively and ONH swelling in the acute stage are essential events for confirming the successful induction of rAION.

A Small Molecule TrkB Neurotrophin Receptor Partial Agonist as Possible Treatment for Experimental Nonarteritic Anterior Ischemic Optic Neuropathy

PURPOSE

Brain-derived neurotrophic factor (BDNF) and activation of its high affinity receptor tropomyosin kinase (Trk) B promote retinal ganglion cells (RGCs) survival following injury. In this study, we tested the effects of LM22A-4, a small molecule TrkB receptor-specific partial agonist, on RGC survival in vitro and in experimental nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in those older than 50 years.

METHODS

We assessed drug effects on immunopanned, cultured RGCs and calculated RGC survival and assessed TrkB receptor activation by mitogen-activated protein (MAP) kinase translocation. To assess effects in vivo, we induced murine AION and treated the animals with one intravitreal injection and three-week systemic treatment. We measured drug effects using serial spectral-domain optical coherence tomography (OCT) and quantified retinal Brn3A+ RGC density three weeks after ischemia.

RESULTS

In vitro, LM22A-4 significantly increased the survival of cultured RGCs at day 2 (95% CI control: 8.4-13.6; LM22A-4: 23.7-30.3; BDNF: 24.3-29.9; P ≤ 0.0001), similar to the effect of the endogenous TrkB receptor ligand BDNF. There was also significant nuclear and cytoplasmic translocation of MAP kinase (95% CI control: 0.9-6.8; LM22A-4: 38.8-84.4; BDNF: 64.0-93.0; P = 0.0002), a known downstream event of TrkB receptor activation. Following AION, LM22A-4 treatment led to significant preservation of the ganglion cell complex (95% CI: AION-PBS: 66.8-70.7%; AION-LM22A-4: 70.0-73.1; P = 0.03) and total retinal thickness (95% CI: AION-PBS: 185-196%; AION-LM22A-4: 195-203; P = 0.002) as measured by OCT compared with non-treated eyes. There was also significant rescue of the Brn3A+ RGC density on morphometric analysis of whole mount retinae (95% CI control: 2360-2629; AION-PBS: 1647-2008 cells/mm2; AION-LM22A-4: 1958-2216 cells/mm2; P = 0.02).

CONCLUSIONS

TrkB receptor partial agonist LM22A-4 promoted survival of cultured RGCs in vitro by TrkB receptor activation, and treatment in vivo led to increased survival of RGCs after optic nerve ischemia, providing support that LM22A-4 may be effective therapy to treat ischemic optic neuropathy.

ABBREVIATIONS

AION: anterior ischemic optic neuropathy, BDNF: Brain-derived neurotrophic factor, GCC: ganglion cell complex, MAP: mitogen-activated protein, OCT: spectral-domain optical coherence tomography, OD: right eye, ON: optic nerve, ONH: optic nerve head, OS: left eye, RGC: retinal ganglion cell; Trk: tropomyosin kinase.

Assessment of Outer Retinal Remodeling in the Hibernating 13-Lined Ground Squirrel

Purpose

We examined outer retinal remodeling of the euthermic and torpid cone-dominant 13-lined ground squirrel (13-LGS) retina using optical coherence tomography (OCT) imaging and histology.

Methods

Retinas and corneas of living 13-LGSs were imaged during euthermic and torpid physiological states using OCT. Retinal layer thickness was measured at the visual streak from registered and averaged vertical B-scans. Following OCT, some retinas were collected immediately for postmortem histologic comparison using light microscopy, immunofluorescence, or transmission electron microscopy.

Results

Compared to OCT images from euthermic retinae, OCT images of torpid retinae revealed significantly thicker inner and outer nuclear layers, as well as increases in the distances between outer retinal reflectivity bands 1 and 2, and bands 3 and 4. A significant decrease in the distance between bands 2 and 3 also was seen, alongside significant thinning of the choriocapillaris and choroid. OCT image quality was reduced in torpid eyes, partly due to significant thickening of the corneal stroma during this state.

Conclusions

The torpid retina of the hibernating 13-LGS undergoes structural changes that can be detected by OCT imaging. Comparisons between in vivo OCT and ex vivo histomorphometry may offer insight to the origin of hyperreflective OCT bands within the outer retina of the cone-dominant 13-LGS.

Cystoid edema, neovascularization and inflammatory processes in the murine Norrin-deficient retina

Mutations in the Norrin (NDP) gene cause severe developmental blood vessel defects in the retina leading to congenital blindness. In the retina of Ndph-knockout mice only the superficial capillary network develops. Here, a detailed characterization of this mouse model at late stages of the disease using in vivo retinal imaging revealed cystoid structures that closely resemble the ovoid cysts in the inner nuclear layer of the human retina with cystoid macular edema (CME). In human CME an involvement of Müller glia cells is hypothesized. In Ndph-knockout retinae we could demonstrate that activated Müller cells were located around and within these cystoid spaces. In addition, we observed extensive activation of retinal microglia and development of neovascularization. Furthermore, ex vivo analyses detected extravasation of monocytic cells suggesting a breakdown of the blood retina barrier. Thus, we could demonstrate that also in the developmental retinal vascular pathology present in the Ndph-knockout mouse inflammatory processes are active and may contribute to further retinal degeneration. This observation delivers a new perspective for curative treatments of retinal vasculopathies. Modulation of inflammatory responses might reduce the symptoms and improve visual acuity in these diseases.