Restoring vision

Visual Cortical Thickness Increases with Prolonged Artificial Vision Restoration

The Argus II retinal prosthesis restores visual perception to late blind patients. It has been shown that structural changes occur in the brain due to late-onset blindness, including cortical thinning in visual regions of the brain. Following vision restoration, it is not yet known whether these visual regions are reinvigorated and regain a normal cortical thickness or retain the diminished thickness from blindness. We evaluated the cortical thicknesses of ten Argus II Retinal Prostheses patients, ten blind patients, and thirteen sighted participants. The Argus II patients on average had a thicker left Cuneus Cortex and Lateral Occipital Cortex relative to the blind patients. The duration of the Argus II use (time since implant in active users) significantly partially correlated with thicker visual cortical regions in the left hemisphere. Furthermore, in the two case studies (scanned before and after implantation), the patient with longer device use (44.5 months) had an increase in the cortical thickness of visual regions, whereas the shorter-using patient did not (6.5 months). Finally, a third case, scanned at three time points post-implantation, showed an increase in cortical thickness in the Lateral Occipital Cortex between 43.5 and 57 months, which was maintained even after 3 years of disuse (106 months). Overall, the Argus II patients' cortical thickness was on average significantly rejuvenated in two higher visual regions and, patients using the implant for a longer duration had thicker visual regions. This research raises the possibility of structural plasticity reversing visual cortical atrophy in late-blind patients with prolonged vision restoration.

Electrophysiological Analysis of Retinal Organoid Development Using 3D Microelectrodes of Liquid Metals

Despite of the substantial potential of human-derived retinal organoids, the degeneration of retinal ganglion cells (RGCs) during maturation limits their utility in assessing the functionality of later-born retinal cell subtypes. Additionally, conventional analyses primarily rely on fluorescent emissions, which limits the detection of actual cell functionality while risking damage to the 3D cytoarchitecture of organoids. Here, an electrophysiological analysis is presented to monitor RGC development in early to mid-stage retinal organoids, and compare distinct features with fully-mature mouse retina. This approach utilizes high-resolution 3D printing of liquid-metal microelectrodes, enabling precise targeting of specific inner retinal layers within organoids. The adaptable distribution and softness of these microelectrodes facilitate the spatiotemporal recording of inner retinal signals. This study not only demonstrates the functional properties of RGCs in retinal organoid development but also provides insights into their synaptic connectivity, reminiscent of fetal native retinas. Further comparison with fully-mature mouse retina in vivo verifies the organoid features, highlighting the potential of early-stage retinal organoids in biomedical research.

Research progress of photo-crosslink hydrogels in ophthalmology: A comprehensive review focus on the applications

Hydrogel presents a three-dimensional polymer network with high water content. Over the past decade, hydrogel has developed from static material to intelligent material with controllable response. Various stimuli are involved in the formation of hydrogel network, among which photo-stimulation has attracted wide attention due to the advantages of controllable conditions, which has a good application prospect in the treatment of ophthalmic diseases. This paper reviews the application of photo-crosslink hydrogels in ophthalmology, focusing on the types of photo-crosslink hydrogels and their applications in ophthalmology, including drug delivery, tissue engineering and 3D printing. In addition, the limitations and future prospects of photo-crosslink hydrogels are also provided.

Automated quantification of photoreceptor outer segments in developing and degenerating retinas on microscopy images across scales

The functionality of photoreceptors, rods, and cones is highly dependent on their outer segments (POS), a cellular compartment containing highly organized membranous structures that generate biochemical signals from incident light. While POS formation and degeneration are qualitatively assessed on microscopy images, reliable methodology for quantitative analyses is still limited. Here, we developed methods to quantify POS (QuaPOS) maturation and quality on retinal sections using automated image analyses. POS formation was examined during the development and in adulthood of wild-type mice via light microscopy (LM) and transmission electron microscopy (TEM). To quantify the number, size, shape, and fluorescence intensity of POS, retinal cryosections were immunostained for the cone POS marker S-opsin. Fluorescence images were used to train the robust classifier QuaPOS-LM based on supervised machine learning for automated image segmentation. Characteristic features of segmentation results were extracted to quantify the maturation of cone POS. Subsequently, this quantification method was applied to characterize POS degeneration in "cone photoreceptor function loss 1" mice. TEM images were used to establish the ultrastructural quantification method QuaPOS-TEM for the alignment of POS membranes. Images were analyzed using a custom-written MATLAB code to extract the orientation of membranes from the image gradient and their alignment (coherency). This analysis was used to quantify the POS morphology of wild-type and two inherited retinal degeneration ("retinal degeneration 19" and "rhodopsin knock-out") mouse lines. Both automated analysis technologies provided robust characterization and quantification of POS based on LM or TEM images. Automated image segmentation by the classifier QuaPOS-LM and analysis of the orientation of membrane stacks by QuaPOS-TEM using fluorescent or TEM images allowed quantitative evaluation of POS formation and quality. The assessments showed an increase in POS number, volume, and membrane coherency during wild-type postnatal development, while a decrease in all three observables was detected in different retinal degeneration mouse models. All the code used for the presented analysis is open source, including example datasets to reproduce the findings. Hence, the QuaPOS quantification methods are useful for in-depth characterization of POS on retinal sections in developmental studies, for disease modeling, or after therapeutic interventions affecting photoreceptors.

Theoretical prediction of broadband ambient light optogenetic vision restoration with ChRmine and its mutants

Vision restoration is one of the most promising applications of optogenetics. However, it is limited due to the poor-sensitivity, slow-kinetics and narrow band absorption spectra of opsins. Here, a detailed theoretical study of retinal ganglion neurons (RGNs) expressed with ChRmine, ReaChR, CoChR, CatCh and their mutants, with near monochromatic LEDs, and broadband sunlight, halogen lamp, RGB LED light, and pure white light sources has been presented. All the opsins exhibit improved light sensitivity and larger photocurrent on illuminating with broadband light sources compared to narrow band LEDs. ChRmine allows firing at ambient sunlight (1.5 nW/mm2) and pure white light (1.2 nW/mm2), which is lowest among the opsins considered. The broadband activation spectrum of ChRmine and its mutants is also useful to restore color sensitivity. Although ChRmine exhibits slower turn-off kinetics with broadband light, high-fidelity spikes can be evoked upto 50 Hz. This limit extends upto 80 Hz with the improved hsChRmine mutant although it requires double the irradiance compared to ChRmine. The present study shows that ChRmine and its mutants allow activation of RGNs with ambient light which is useful for goggle-free white light optogenetic retinal prostheses with improved quality of restored vision.

Development and Validation of a Novel Mobility Test for Rod-Cone Dystrophies: From Reality to Virtual Reality

PURPOSE

To validate a novel mobility test (MOST, MObility Standardized Test) and performance outcomes in real (RL) and virtual (VR) environments to be used for interventional clinical studies in order to characterize vision impairment in rod-cone dystrophies, also known as retinitis pigmentosa (RP).

DESIGN

Prospective, interventional, noninvasive, reliability and validity analysis.

METHODS

We designed MOST to be used in both VR and RL and conducted 3 experimental studies with 89 participants to (1) validate the difficulty of the mobility courses (15 controls), (2) determine the optimal number of light levels and training trials (14 participants with RP), and (3) validate the reproducibility (test-retest), reliability (VR/RL), sensitivity, and construct/content validity of the test (30 participants with RP and 30 controls). A comprehensive ophthalmologic examination was performed in all subjects. Outcomes of interest included MOST performance score, visual acuity, contrast sensitivity, dark adaptation thresholds, visual field parameters, and correlation between the performance score and visual function.

RESULTS

The mobility courses exhibited statistically similar difficulty, and 5 trials are sufficient to control for the learning effect. MOST is highly reproducible (test-retest correlations >0.98) and reliable (correlations VR/RL = 0.98). MOST achieved a discrimination between participants with RP and controls (accuracy >95%) and between early and late stages of the disease (82.3% accuracy). The performance score is correlated with visual function parameter (0.57-0.94).

CONCLUSION

MOST is a validated mobility test, with the controlled learning effect, excellent reproducibility, and high agreement between RL and VR conditions, as well as sensitivity and specificity to measure disease progression and therapeutic benefit in rod-cone dystrophies.

Development of a simplified human embryonic stem cell-based retinal pre-organoid model for toxicity evaluations of common pollutants

OBJECTIVE

To explore the retinal toxicity of pharmaceuticals and personal care products (PPCPs), flame retardants, bisphenols, phthalates, and polycyclic aromatic hydrocarbons (PAHs) on human retinal progenitor cells (RPCs) and retinal pigment epithelial (RPE) cells, which are the primary cell types at the early stages of retinal development, vital for subsequent functional cell type differentiation, and closely related to retinal diseases.

MATERIALS AND METHODS

After 23 days of differentiation, human embryonic stem cell (hESC)-based retinal pre-organoids, containing RPCs and RPE cells, were exposed to 10, 100, and 1000 nM pesticides (butachlor, terbutryn, imidacloprid, deltamethrin, pendimethalin, and carbaryl), flame retardants (PFOS, TBBPA, DBDPE, and TDCIPP), PPCPs (climbazole and BHT), and other typical pollutants (phenanthrene, DCHP, and BPA) for seven days. Then, mRNA expression changes were monitored and compared.

RESULTS

(1) The selected pollutants did not show strong effects at environmental and human-relevant concentrations, although the effects of flame retardants were more potent than those of other categories of chemicals. Surprisingly, some pollutants with distinct structures showed similar adverse effects. (2) Exposure to pollutants induced different degrees of cell detachment, probably due to alterations in extracellular matrix and/or cell adhesion.

CONCLUSIONS

In this study, we established a retinal pre-organoid model suitable for evaluating multiple pollutants' effects, and pointed out the potential retinal toxicity of flame retardants, among other pollutants. Nevertheless, the potential mechanisms of toxicity and the effects on cell detachment are still unclear and deserve further exploration. Additionally, this model holds promise for screening interventions aimed at mitigating the detrimental effects of these pollutants.

Assessment of visual function in blind mice and monkeys with subretinally implanted nanowire arrays as artificial photoreceptors

Retinal prostheses could restore image-forming vision in conditions of photoreceptor degeneration. However, contrast sensitivity and visual acuity are often insufficient. Here we report the performance, in mice and monkeys with induced photoreceptor degeneration, of subretinally implanted gold-nanoparticle-coated titania nanowire arrays providing a spatial resolution of 77.5 μm and a temporal resolution of 3.92 Hz in ex vivo retinas (as determined by patch-clamp recording of retinal ganglion cells). In blind mice, the arrays allowed for the detection of drifting gratings and flashing objects at light-intensity thresholds of 15.70-18.09 μW mm-2, and offered visual acuities of 0.3-0.4 cycles per degree, as determined by recordings of visually evoked potentials and optomotor-response tests. In monkeys, the arrays were stable for 54 weeks, allowed for the detection of a 10-μW mm-2 beam of light (0.5° in beam angle) in visually guided saccade experiments, and induced plastic changes in the primary visual cortex, as indicated by long-term in vivo calcium imaging. Nanomaterials as artificial photoreceptors may ameliorate visual deficits in patients with photoreceptor degeneration.

Optogenetic activation of visual thalamus generates artificial visual percepts

The lateral geniculate nucleus (LGN), a retinotopic relay center where visual inputs from the retina are processed and relayed to the visual cortex, has been proposed as a potential target for artificial vision. At present, it is unknown whether optogenetic LGN stimulation is sufficient to elicit behaviorally relevant percepts, and the properties of LGN neural responses relevant for artificial vision have not been thoroughly characterized. Here, we demonstrate that tree shrews pretrained on a visual detection task can detect optogenetic LGN activation using an AAV2-CamKIIα-ChR2 construct and readily generalize from visual to optogenetic detection. Simultaneous recordings of LGN spiking activity and primary visual cortex (V1) local field potentials (LFPs) during optogenetic LGN stimulation show that LGN neurons reliably follow optogenetic stimulation at frequencies up to 60 Hz and uncovered a striking phase locking between the V1 LFP and the evoked spiking activity in LGN. These phase relationships were maintained over a broad range of LGN stimulation frequencies, up to 80 Hz, with spike field coherence values favoring higher frequencies, indicating the ability to relay temporally precise information to V1 using light activation of the LGN. Finally, V1 LFP responses showed sensitivity values to LGN optogenetic activation that were similar to the animal's behavioral performance. Taken together, our findings confirm the LGN as a potential target for visual prosthetics in a highly visual mammal closely related to primates.

Establishing Functional Retina in a Dish: Progress and Promises of Induced Pluripotent Stem Cell-Based Retinal Neuron Differentiation

The human eye plays a critical role in vision perception, but various retinal degenerative diseases such as retinitis pigmentosa (RP), glaucoma, and age-related macular degeneration (AMD) can lead to vision loss or blindness. Although progress has been made in understanding retinal development and in clinical research, current treatments remain inadequate for curing or reversing these degenerative conditions. Animal models have limited relevance to humans, and obtaining human eye tissue samples is challenging due to ethical and legal considerations. Consequently, researchers have turned to stem cell-based approaches, specifically induced pluripotent stem cells (iPSCs), to generate distinct retinal cell populations and develop cell replacement therapies. iPSCs offer a novel platform for studying the key stages of human retinogenesis and disease-specific mechanisms. Stem cell technology has facilitated the production of diverse retinal cell types, including retinal ganglion cells (RGCs) and photoreceptors, and the development of retinal organoids has emerged as a valuable in vitro tool for investigating retinal neuron differentiation and modeling retinal diseases. This review focuses on the protocols, culture conditions, and techniques employed in differentiating retinal neurons from iPSCs. Furthermore, it emphasizes the significance of molecular and functional validation of the differentiated cells.

Inducible nonhuman primate models of retinal degeneration for testing end-stage therapies

The anatomical differences between the retinas of humans and most animal models pose a challenge for testing novel therapies. Nonhuman primate (NHP) retina is anatomically closest to the human retina. However, there is a lack of relevant NHP models of retinal degeneration (RD) suitable for preclinical studies. To address this unmet need, we generated three distinct inducible cynomolgus macaque models of RD. We developed two genetically targeted strategies using optogenetics and CRISPR-Cas9 to ablate rods and mimic rod-cone dystrophy. In addition, we created an acute model by physical separation of the photoreceptors and retinal pigment epithelium using a polymer patch. Among the three models, the CRISPR-Cas9-based approach was the most advantageous model in view of recapitulating disease-specific features and its ease of implementation. The acute model, however, resulted in the fastest degeneration, making it the most relevant model for testing end-stage vision restoration therapies such as stem cell transplantation.

Bio-Inspired Design of Superconducting Spiking Neuron and Synapse

The imitative modelling of processes in the brain of living beings is an ambitious task. However, advances in the complexity of existing hardware brain models are limited by their low speed and high energy consumption. A superconducting circuit with Josephson junctions closely mimics the neuronal membrane with channels involved in the operation of the sodium-potassium pump. The dynamic processes in such a system are characterised by a duration of picoseconds and an energy level of attojoules. In this work, two superconducting models of a biological neuron are studied. New modes of their operation are identified, including the so-called bursting mode, which plays an important role in biological neural networks. The possibility of switching between different modes in situ is shown, providing the possibility of dynamic control of the system. A synaptic connection that mimics the short-term potentiation of a biological synapse is developed and demonstrated. Finally, the simplest two-neuron chain comprising the proposed bio-inspired components is simulated, and the prospects of superconducting hardware biosimilars are briefly discussed.

MAP4Ks inhibition promotes retinal neuron regeneration from Müller glia in adult mice

Mammalian Müller glia (MG) possess limited regenerative capacities. However, the intrinsic capacity of mammalian MG to transdifferentiate to generate mature neurons without transgenic manipulations remains speculative. Here we show that MAP4K4, MAP4K6 and MAP4K7, which are conserved Misshapen subfamily of ste20 kinases homologs, repress YAP activity in mammalian MG and therefore restrict their ability to be reprogrammed. However, by treating with a small molecule inhibitor of MAP4K4/6/7, mouse MG regain their ability to proliferate and enter into a retinal progenitor cell (RPC)-like state after NMDA-induced retinal damage; such plasticity was lost in YAP knockout MG. Moreover, spontaneous trans-differentiation of MG into retinal neurons expressing both amacrine and retinal ganglion cell (RGC) markers occurs after inhibitor withdrawal. Taken together, these findings suggest that MAP4Ks block the reprogramming capacity of MG in a YAP-dependent manner in adult mammals, which provides a novel avenue for the pharmaceutical induction of retinal regeneration in vivo.

Attitudes of potential recipients toward emerging visual prosthesis technologies

With the advent of multiple visual prosthesis devices to treat blindness, the question of how potential patients view such interventions becomes important in order to understand the levels of expectation and acceptance, and the perceived risk-reward balance across the different device approaches. Building on previous work on single device approaches done with blind individuals in Chicago and Detroit, USA, Melbourne, Australia, and Bejing, China, we investigated attitudes in blind individuals in Athens, Greece with coverage expanded to three of the contemporary approaches, Retinal, Thalamic, and Cortical. We presented an informational lecture on the approaches, had potential participants fill out a preliminary Questionnaire 1, then organized selected subjects into focus groups for guided discussion on visual prostheses, and finally had these subjects fill out a more detailed Questionnaire 2. We report here the first quantitative data that compares multiple prosthesis approaches. Our primary findings are that for these potential patients, perceived risk continues to outweigh perceived benefits, with the Retinal approach having the least negative overall impression and the Cortical approach the most negative. Concerns about the quality of restored vision were primary. Factors that drove the choice of hypothetical participation in a clinical trial were age and years of blindness. Secondary factors focused on positive clinical outcomes. The focus groups served to swing the impressions of each approach from neutrality toward the extremes of a Likert scale, and shifted the overall willingness to participate in a clinical trial from neutral to negative. These results, coupled with informal assessment of audience questions after the informational lecture, suggest that a substantial improvement in performance over currently available devices will be necessary before visual prostheses gain wide acceptance.

Chronic stability of a neuroprosthesis comprising multiple adjacent Utah arrays in monkeys

Objective. Electrical stimulation of visual cortex via a neuroprosthesis induces the perception of dots of light ('phosphenes'), potentially allowing recognition of simple shapes even after decades of blindness. However, restoration of functional vision requires large numbers of electrodes, and chronic, clinical implantation of intracortical electrodes in the visual cortex has only been achieved using devices of up to 96 channels. We evaluated the efficacy and stability of a 1024-channel neuroprosthesis system in non-human primates (NHPs) over more than 3 years to assess its suitability for long-term vision restoration.Approach.We implanted 16 microelectrode arrays (Utah arrays) consisting of 8 × 8 electrodes with iridium oxide tips in the primary visual cortex (V1) and visual area 4 (V4) of two sighted macaques. We monitored the animals' health and measured electrode impedances and neuronal signal quality by calculating signal-to-noise ratios of visually driven neuronal activity, peak-to-peak voltages of the waveforms of action potentials, and the number of channels with high-amplitude signals. We delivered cortical microstimulation and determined the minimum current that could be perceived, monitoring the number of channels that successfully yielded phosphenes. We also examined the influence of the implant on a visual task after 2-3 years of implantation and determined the integrity of the brain tissue with a histological analysis 3-3.5 years post-implantation.Main results. The monkeys remained healthy throughout the implantation period and the device retained its mechanical integrity and electrical conductivity. However, we observed decreasing signal quality with time, declining numbers of phosphene-evoking electrodes, decreases in electrode impedances, and impaired performance on a visual task at visual field locations corresponding to implanted cortical regions. Current thresholds increased with time in one of the two animals. The histological analysis revealed encapsulation of arrays and cortical degeneration. Scanning electron microscopy on one array revealed degradation of IrOxcoating and higher impedances for electrodes with broken tips.Significance. Long-term implantation of a high-channel-count device in NHP visual cortex was accompanied by deformation of cortical tissue and decreased stimulation efficacy and signal quality over time. We conclude that improvements in device biocompatibility and/or refinement of implantation techniques are needed before future clinical use is feasible.

Postsynaptic neuronal activity promotes regeneration of retinal axons

The wiring of visual circuits requires that retinal neurons functionally connect to specific brain targets, a process that involves activity-dependent signaling between retinal axons and their postsynaptic targets. Vision loss in various ophthalmological and neurological diseases is caused by damage to the connections from the eye to the brain. How postsynaptic brain targets influence retinal ganglion cell (RGC) axon regeneration and functional reconnection with the brain targets remains poorly understood. Here, we established a paradigm in which the enhancement of neural activity in the distal optic pathway, where the postsynaptic visual target neurons reside, promotes RGC axon regeneration and target reinnervation and leads to the rescue of optomotor function. Furthermore, selective activation of retinorecipient neuron subsets is sufficient to promote RGC axon regeneration. Our findings reveal a key role for postsynaptic neuronal activity in the repair of neural circuits and highlight the potential to restore damaged sensory inputs via proper brain stimulation.

Pollution effects on retinal health: A review on current methodologies and findings

In our daily life, we are exposed to numerous industrial chemicals that may be harmful to the retina, which is a delicate and sensitive part of our eyes. This could lead to irreversible changes and cause retinal diseases or blindness. Current retinal environmental health studies primarily utilize animal models, isolated mammalian retinas, animal- or human-derived retinal cells, and retinal organoids, to address both pre- and postnatal exposure. However, as there is limited toxicological information available for specific populations, human induced pluripotent stem cell (hiPSC)-induced models could be effective tools to supplement such data. In order to obtain more comprehensive and reliable toxicological information, we need more appropriate models, novel evaluation methods, and computational technologies to develop portable equipment. This review mainly focused on current toxicology models with particular emphasis on retinal organoids, and it looks forward to future models, analytical methods, and equipment that can efficiently and accurately evaluate retinal toxicity.

The Mediterranean Diet and Age-Related Eye Diseases: A Systematic Review

The Mediterranean diet (MD) is a healthy diet pattern that can prevent chronic age-related diseases, especially age-related eye diseases (AREDs) including cataract, glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR) and dry eye syndrome (DES). In this study, we systematically reviewed studies in the literature that had reported associations between adherence to the MD and the five above-mentioned AREDs. Randomized controlled trials as well as prospective and retrospective observational studies were included; 1164 studies were identified, of which 1, 2, 9, 2 and 4 studies met our eligibility criteria for cataract, glaucoma, AMD, DR, and DES, respectively. According to these studies, higher MD adherence was associated with reduced risks of incident DR, incident AMD and progression to late AMD, but whether early and neovascular AMD could be alleviated remained to be debated. The results regarding the effects of the MD on DES were mixed, with three studies reporting an associations between MD and decreased severity or incidence of DES, whereas one study reported the opposite. No significant associations were observed between the MD and cataract or glaucoma. Generally, convincing evidence suggested a protective effect of the MD against AMD and DR. However, the evidence for cataract, glaucoma, and DES was less conclusive, and high-quality studies are needed for comprehensive evaluations of the potential benefits of MD on these eye diseases.

Nano-based eye drop: Topical and noninvasive therapy for ocular diseases

Eye drops are the most accessible therapy for ocular diseases, while inevitably suffering from their lower bioavailability which highly restricts the treatment efficacy. The introduction of nanotechnology has attracted considerable interest as it has advantages over conventional ones such as prolonged ocular surface retention time and enhanced ocular barrier penetrating properties, and achieving higher bioavailability and improved treatment efficacy. This review describes various ocular diseases treated with eye drops as well as the physiological and anatomical ocular barriers faced with through drug administration. It also summarizes the recent advances regarding the utilization of nanotechnology in developing eye drops, and how to optimize the nanocarrier-based ocular drug delivery systems. The prospective future research directions for nano-based eye drops are also discussed here.

Photoreceptor Cell Replacement Using Pluripotent Stem Cells: Current Knowledge and Remaining Questions

Retinal degeneration is an increasing global burden without cure for the majority of patients. Once retinal cells have degenerated, vision is permanently lost. Different strategies have been developed in recent years to prevent retinal degeneration or to restore sight (e.g., gene therapy, cell therapy, and electronic implants). Herein, we present current treatment strategies with a focus on cell therapy for photoreceptor replacement using human pluripotent stem cells. We will describe the state of the art and discuss obstacles and limitations observed in preclinical animal models as well as future directions to improve graft integration and functionality.

Sox11b regulates the migration and fate determination of Müller glia-derived progenitors during retina regeneration in zebrafish

The transcription factor Sox11 plays important roles in retinal neurogenesis during vertebrate eye development. However, its function in retina regeneration remains elusive. Here we report that Sox11b, a zebrafish Sox11 homolog, regulates the migration and fate determination of Müller glia-derived progenitors (MGPCs) in an adult zebrafish model of mechanical retinal injury. Following a stab injury, the expression of Sox11b was induced in proliferating MGPCs in the retina. Sox11b knockdown did not affect MGPC formation at 4 days post-injury, although the nuclear morphology and subsequent radial migration of MGPCs were altered. At 7 days post-injury, Sox11b knockdown resulted in an increased proportion of MGPCs in the inner retina and a decreased proportion of MGPCs in the outer nuclear layer, compared with controls. Furthermore, Sox11b knockdown led to reduced photoreceptor regeneration, while it increased the numbers of newborn amacrines and retinal ganglion cells. Finally, quantitative polymerase chain reaction analysis revealed that Sox11b regulated the expression of Notch signaling components in the retina, and Notch inhibition partially recapitulated the Sox11b knockdown phenotype, indicating that Notch signaling functions downstream of Sox11b. Our findings imply that Sox11b plays key roles in MGPC migration and fate determination during retina regeneration in zebrafish, which may have critical implications for future explorations of retinal repair in mammals.

Network Biology and Medicine to Rescue: Applications for Retinal Disease Mechanisms and Therapy

Inherited retinal degenerations (IRDs) are clinically and genetically heterogenous blinding diseases that manifest through dysfunction of target cells, photoreceptors, and retinal pigment epithelium (RPE) in the retina. Despite knowledge of numerous underlying genetic defects, current therapeutic approaches, including gene centric applications, have had limited success, thereby asserting the need of new directions for basic and translational research. Human diseases have commonalities that can be represented in a network form, called diseasome, which captures relationships among disease genes, proteins, metabolites, and patient meta-data. Clinical and genetic information of IRDs suggest shared relationships among pathobiological factors, making these a model case for network medicine. Characterization of the diseasome would considerably improve our understanding of retinal pathologies and permit better design of targeted therapies for disrupted regions within the integrated disease network. Network medicine in synergy with the ongoing artificial intelligence revolution can boost therapeutic developments, especially gene agnostic treatment opportunities.

Structural and functional distinctions of co-resident microglia and monocyte-derived macrophages after retinal degeneration

BACKGROUND

Both resident microglia and invading peripheral immune cells can respond to injury and degeneration in the central nervous system. However, after dead and dying neurons have been cleared and homeostasis is re-established, it is unknown whether resident immune cells fully resume normal functions and to what degree the peripheral immune cells take up residence.

METHODS

Using flow cytometry, in vivo retinal imaging, immunohistochemistry, and single-cell mRNA sequencing, we assess resident microglia and monocyte-derived macrophages in the retina during and after the loss of photoreceptors in the Arr1^-/- mouse model of inducible degeneration.

RESULTS

We find that photoreceptor loss results in a small, sustained increase in mononuclear phagocytes and, after degeneration wanes, these cells re-establish a spatial mosaic reminiscent of healthy retinas. Transcriptomic analysis revealed the population remained unusually heterogeneous, with several subpopulations expressing gene patterns consistent with mildly activated phenotypes. Roughly a third of "new resident" cells expressed markers traditionally associated with both microglial and monocytic lineages, making their etiology ambiguous. Using an inducible Cre-based fluorescent lineage tracing paradigm to confirm the origins of new resident immune cells, we found approximately equal numbers of microglia and monocyte-derived macrophages after degeneration had subsided. In vivo retinal imaging and immunohistochemical analysis showed that both subpopulations remained functionally responsive to sites of local damage, though on average the monocyte-derived cells had less morphological complexity, expressed higher levels of MHCII, and had less migratory activity than the native resident population.

CONCLUSIONS

Monocytic cells that infiltrate the retina during degeneration differentiate into monocyte-derived macrophages that can remain in the retina long-term. These monocyte-derived macrophages adopt ramified morphologies and microglia-like gene expression. However, they remain distinguishable in morphology and gene expression from resident microglia and appear to differ functionally, showing less responsiveness to subsequent retinal injuries. These findings support the idea that persistent changes in the local immune population that occur in response to cell loss in aging and progressive retinal diseases may include the establishment of subpopulations of bone marrow-derived cells whose ability to respond to subsequent insults wanes over time.

Towards aSmart Bionic Eye: AI-powered artificial vision for the treatment of incurable blindness

Objective.How can we return a functional form of sight to people who are living with incurable blindness? Despite recent advances in the development of visual neuroprostheses, the quality of current prosthetic vision is still rudimentary and does not differ much across different device technologies.Approach.Rather than aiming to represent the visual scene as naturally as possible, aSmart Bionic Eyecould provide visual augmentations through the means of artificial intelligence-based scene understanding, tailored to specific real-world tasks that are known to affect the quality of life of people who are blind, such as face recognition, outdoor navigation, and self-care.Main results.Complementary to existing research aiming to restore natural vision, we propose a patient-centered approach to incorporate deep learning-based visual augmentations into the next generation of devices.Significance.The ability of a visual prosthesis to support everyday tasks might make the difference between abandoned technology and a widely adopted next-generation neuroprosthetic device.

Ex Vivo Integration of Human Stem Retinal Ganglion Cells into the Mouse Retina

Cell replacement therapies may be key in achieving functional recovery in neurodegenerative optic neuropathies diseases such as glaucoma. One strategy that holds promise in this regard is the use of human embryonic stem cell and induced pluripotent stem-derived retinal ganglion cells (hRGCs). Previous hRGC transplantation studies have shown modest success. This is in part due to the low survival and integration of the transplanted cells in the host retina. The field is further challenged by mixed assays and outcome measurements that probe and determine transplantation success. Thefore, we have devised a transplantation assay involving hRGCs and mouse retina explants that bypasses physical barriers imposed by retinal membranes. We show that hRGC neurites and somas are capable of invading mouse explants with a subset of hRGC neurites being guided by mouse RGC axons. Neonatal mouse retina explants, and to a lesser extent, adult explants, promote hRGC integrity and neurite outgrowth. Using this assay, we tested whether suppmenting cultures with brain derived neurotrophic factor (BDNF) and the adenylate cyclase activator, forskolin, enhances hRGC neurite integration, neurite outgrowth, and integrity. We show that supplementing cultures with a combination BDNF and forskolin strongly favors hRGC integrity, increasing neurite outgrowth and complexity as well as the invasion of mouse explants. The transplantation assay presented here is a practical tool for investigating strategies for testing and optimizing the integration of donor cells into host tissues.

Homeostatic plasticity in the retina

Vision begins in the retina, whose intricate neural circuits extract salient features of the environment from the light entering our eyes. Neurodegenerative diseases of the retina (e.g., inherited retinal degenerations, age-related macular degeneration, and glaucoma) impair vision and cause blindness in a growing number of people worldwide. Increasing evidence indicates that homeostatic plasticity (i.e., the drive of a neural system to stabilize its function) can, in principle, preserve retinal function in the face of major perturbations, including neurodegeneration. Here, we review the circumstances and events that trigger homeostatic plasticity in the retina during development, sensory experience, and disease. We discuss the diverse mechanisms that cooperate to compensate and the set points and outcomes that homeostatic retinal plasticity stabilizes. Finally, we summarize the opportunities and challenges for unlocking the therapeutic potential of homeostatic plasticity. Homeostatic plasticity is fundamental to understanding retinal development and function and could be an important tool in the fight to preserve and restore vision.

All-optical inter-layers functional connectivity investigation in the mouse retina

We developed a multi-unit microscope for all-optical inter-layers circuits interrogation. The system performs two-photon (2P) functional imaging and 2P multiplexed holographic optogenetics at axially distinct planes. We demonstrated the capability of the system to map, in the mouse retina, the functional connectivity between rod bipolar cells (RBCs) and ganglion cells (GCs) by activating single or defined groups of RBCs while recording the evoked response in the GC layer with cell-type specificity and single-cell resolution. We then used a logistic model to probe the functional connectivity between cell types by deriving the "cellular receptive field" describing how RBCs impact each GC type. With the capability to simultaneously image and control neuronal activity at axially distinct planes, the system enables a precise interrogation of multi-layered circuits. Understanding this information transfer is a promising avenue to dissect complex neural circuits and understand the neural basis of computations.

Flexible ultrasound-induced retinal stimulating piezo-arrays for biomimetic visual prostheses

Electronic visual prostheses, or biomimetic eyes, have shown the feasibility of restoring functional vision in the blind through electrical pulses to initiate neural responses artificially. However, existing visual prostheses predominantly use wired connections or electromagnetic waves for powering and data telemetry, which raises safety concerns or couples inefficiently to miniaturized implant units. Here, we present a flexible ultrasound-induced retinal stimulating piezo-array that can offer an alternative wireless artificial retinal prosthesis approach for evoking visual percepts in blind individuals. The device integrates a two-dimensional piezo-array with 32-pixel stimulating electrodes in a flexible printed circuit board. Each piezo-element can be ultrasonically and individually activated, thus, spatially reconfigurable electronic patterns can be dynamically applied via programmable ultrasound beamlines. As a proof of concept, we demonstrate the ultrasound-induced pattern reconstruction in ex vivo murine retinal tissue, showing the potential of this approach to restore functional, life-enhancing vision in people living with blindness.

The Transcriptome Profile of Retinal Pigment Epithelium and Müller Cell Lines Protected by Risuteganib Against Hydrogen Peroxide Stress

Purpose:

Oxidative stress contributes to the pathogenesis of vision-impairing diseases. In the retina, retinal pigment epithelium (RPE) and Müller cells support neuronal homeostasis, but also contribute to pathological development under stressed conditions. Recent studies found that the investigational drug risuteganib (RSG) has a good safety profile, provided protection in experimental models, and improved visual acuity in patients. The present in vitro study evaluated the effects of RSG in RPE and Müller cell lines stressed with the oxidant hydrogen peroxide (H₂O₂).

Methods:

Human RPE (ARPE-19) and Müller (MIO-M1) cell lines were treated with various combinations of RSG and H₂O₂. Trypan blue assay was used to investigate the effect of compounds on cell viability. Gene expression was measured using RNA sequencing to identify regulated genes and the biological processes and pathways involved.

Results:

Trypan blue assay found RSG pre-treatment significantly protected against H₂O₂-induced cell death in ARPE-19 and MIO-M1 cells. Transcriptome analysis found H₂O₂ regulated genes in several disease-relevant biological processes, including cell adhesion, migration, death, and proliferation; ECM organization; angiogenesis; metabolism; and immune system processes. RSG pre-treatment modulated these gene expression profiles in the opposite direction of H₂O₂. Pathway analysis found genes in integrin, AP-1, and syndecan signaling pathways were regulated. Expression of selected RSG-regulated genes was validated using qRT-PCR.

Conclusions:

RSG protected cultured human RPE and Müller cell lines against H₂O₂-induced cell death and mitigated the associated transcriptome changes in biological processes and pathways relevant to the pathogenesis of retinal diseases. These results demonstrate RSG reduced oxidative stress-induced toxicity in two retinal cell lines with potential relevance to the treatment of human diseases.

Context-dependent effects of inflammation on retina regeneration

Inflammation is required for the proliferation of Müller glia (MG) into multipotent progenitors (MGPCs) in the injured fish and avian retinas. However, its function in retina regeneration has not been fully understood. Here we investigated the role of inflammation in three different retinal regeneration paradigms in zebrafish (stab-injury, NMDA-injury and insulin treatment). We first show that different types of immune cells and levels of inflammatory cytokines were found in the retinas of these paradigms. Though zymosan injection alone was insufficient to induce MG proliferation in the uninjured retina, immune suppression significantly inhibited MGPC formation in all three paradigms. Enhancing inflammation promoted MGPC formation after stab-injury, while exhibiting a context-dependent role in the NMDA or insulin models. We further show that proper levels of inflammation promoted MG reprogramming and cell cycle re-entry after stab- or NMDA-injury, but excessive inflammation also suppressed MG proliferation in the latter model. Finally, inflammation differentially affected neuronal regeneration in various injury paradigms. Our study reveals the complex and context-dependent role of inflammation during retinal repair in fish and suggests accurate inflammation management may be crucial for successful retina regeneration in mammals.

Full-field sensitivity threshold and the relation to the oxygen metabolic retinal function in retinitis pigmentosa

PURPOSE

The aim of our study was to evaluate retinal function with white light dark-adapted full-field sensitivity threshold (FST) and find possible correlations with metabolic function measured with retinal oximetry (RO) in patients with retinitis pigmentosa (RP).

METHODS

In this prospective observational study (BASEC 2020-00,122), FST and RO measurements were performed on 66 RP eyes (33 subjects, 12♀ 21♂) aged between 18 and 80 years (mean 43.2 years); all eyes were graded for disease severity. Main outcome parameters were white FST thresholds using the Diagnosys Espion system with the ColorDomeTM LED full-field stimulator (Diagnosys LLC, Lowell, MA) as well as the main RO parameters: the mean arterial (A-SO₂; %), venular (V-SO₂; %) oxygen saturation, their difference (A-V SO₂; %), and the corresponding mean diameters of the peripapillary retinal arterioles (D-A; μm) and venules (D-V; μm) recorded with the oxygen saturation tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). In addition, semi-automated kinetic perimetry (V4e, III4e, I4e, III3e isopters, Octopus 900®, Haag-Streit AG Bern, Switzerland) was performed and included in the linear mixed-effects models analysis calculated with SPSS®.

RESULTS

Neither the oxygen saturation parameters (p > 0.21) nor the D-A and D-V (p > 0.13) showed significant correlations with the FST. However, when compared systematically with the visual field (VF) areas of the different isopters, RO parameters V-SO₂ (p = 0.024) and A-V SO₂ (p < 0.02) showed significant correlations. Furthermore, both V-SO₂ and A-V SO₂ showed gradual changes with more pronounced impairment in oxygen metabolic function in advanced stages of RP when analyzed in subgroups of disease severity grades.

CONCLUSION

In contrast to standardized VF parameters, white dark-adapted FST appears not to correlate with retinal oxygen metabolic function measured with RO in patients with RP, suggesting that the two examinations may capture unrelated aspects of the retinal pathological process. However, RO showed a significant association with standardized VF testing parameters and may, therefore, offer an alternative outcome measure for interventional trials.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood–retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Retinal Organoids and Retinal Prostheses: An Overview

Despite the progress of modern medicine in the last decades, millions of people diagnosed with retinal dystrophies (RDs), such as retinitis pigmentosa, or age-related diseases, such as age-related macular degeneration, are suffering from severe visual impairment or even legal blindness. On the one hand, the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) and the progress of three-dimensional (3D) retinal organoids (ROs) technology provide a great opportunity to study, understand, and even treat retinal diseases. On the other hand, research advances in the field of electronic retinal prosthesis using inorganic photovoltaic polymers and the emergence of organic semiconductors represent an encouraging therapeutical strategy to restore vision to patients at the late onset of the disease. This review will provide an overview of the latest advancement in both fields. We first describe the retina and the photoreceptors, briefly mention the most used RD animal models, then focus on the latest RO differentiation protocols, carry out an overview of the current technology on inorganic and organic retinal prostheses to restore vision, and finally summarize the potential utility and applications of ROs.

Visual-tactile shape perception in the visually restored with artificial vision

Retinal prostheses partially restore vision to late blind patients with retinitis pigmentosa through electrical stimulation of still-viable retinal ganglion cells. We investigated whether the late blind can perform visual–tactile shape matching following the partial restoration of vision via retinal prostheses after decades of blindness.

We tested for visual–visual, tactile–tactile, and visual–tactile two-dimensional shape matching with six Argus II retinal prosthesis patients, ten sighted controls, and eight sighted controls with simulated ultra-low vision. In the Argus II patients, the visual–visual shape matching performance was significantly greater than chance. Although the visual–tactile shape matching performance of the Argus II patients was not significantly greater than chance, it was significantly higher with longer duration of prosthesis use. The sighted controls using natural vision and the sighted controls with simulated ultra-low vision both performed the visual–visual and visual–tactile shape matching tasks significantly more accurately than the Argus II patients. The tactile–tactile matching was not significantly different between the Argus II patients and sighted controls with or without simulated ultra-low vision.

These results show that experienced retinal prosthesis patients can match shapes across the senses and integrate artificial vision with somatosensation. The correlation of retinal prosthesis patients’ crossmodal shape matching performance with the duration of device use supports the value of experience to crossmodal shape learning. These crossmodal shape matching results in Argus II patients are the first step toward understanding crossmodal perception after artificial visual restoration.

Multiomics analyses reveal early metabolic imbalance and mitochondrial stress in neonatal photoreceptors leading to cell death in Pde6brd1/rd1 mouse model of retinal degeneration

Retinal diseases exhibit extensive genetic heterogeneity and complex etiology with varying onset and severity. Mutations in over 200 genes can lead to photoreceptor dysfunction and/or cell death in retinal neurodegeneration. To deduce molecular pathways that initiate and/or drive cell death, we adopted a temporal multiomics approach and examined molecular and cellular events in newborn and developing photoreceptors before the onset of degeneration in a widely-used Pde6brd1/rd1 (rd1) mouse, a model of autosomal recessive retinitis pigmentosa caused by PDE6B mutations. Transcriptome profiling of neonatal and developing rods from the rd1 retina revealed early downregulation of genes associated with anabolic pathways and energy metabolism. Quantitative proteomics of rd1 retina showed early changes in calcium signaling and oxidative phosphorylation, with specific partial bypass of complex I electron transfer, which precede the onset of cell death. Concurrently, we detected alterations in central carbon metabolism, including dysregulation of components associated with glycolysis, pentose phosphate and purine biosynthesis. Ex vivo assays of oxygen consumption and transmission electron microscopy validated early and progressive mitochondrial stress and abnormalities in mitochondrial structure and function of rd1 rods. These data uncover mitochondrial overactivation and related metabolic alterations as determinants of early pathology and implicate aberrant calcium signaling as an initiator of higher mitochondrial stress. Our studies thus provide a mechanistic framework with mitochondrial damage and metabolic disruptions as early drivers of photoreceptor cell death in retinal degeneration.

CD82 protects against glaucomatous axonal transport deficits via mTORC1 activation in mice

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive optic nerve degeneration and retinal ganglion cell loss. Axonal transport deficits have been demonstrated to be the earliest crucial pathophysiological changes underlying axonal degeneration in glaucoma. Here, we explored the role of the tetraspanin superfamily member CD82 in an acute ocular hypertension model. We found a transient downregulation of CD82 after acute IOP elevation, with parallel emergence of axonal transport deficits. The overexpression of CD82 with an AAV2/9 vector in the mouse retina improved optic nerve axonal transport and ameliorated subsequent axon degeneration. Moreover, the CD82 overexpression stimulated optic nerve regeneration and restored vision in a mouse optic nerve crush model. CD82 exerted a protective effect through the upregulation of TRAF2, which is an E3 ubiquitin ligase, and activated mTORC1 through K63-linked ubiquitylation and intracellular repositioning of Raptor. Therefore, our study offers deeper insight into the tetraspanin superfamily and demonstrates a potential neuroprotective strategy in glaucoma treatment.

Learning to see again: Perceptual learning of simulated abnormal on- off-cell population responses in sighted individuals

Many forms of artificial sight recovery, such as electronic implants and optogenetic proteins, generally cause simultaneous, rather than complementary firing of on- and off-center retinal cells. Here, using virtual patients—sighted individuals viewing distorted input—we examine whether plasticity might compensate for abnormal neuronal population responses. Five participants were dichoptically presented with a combination of original and contrast-reversed images. Each image (I) and its contrast-reverse (Iʹ) was filtered using a radial checkerboard (F) in Fourier space and its inverse (Fʹ). [I * F′] + [Iʹ * F] was presented to one eye, and [I * F] + [Iʹ * F′] was presented to the other, such that regions of the image that produced on-center responses in one eye produced off-center responses in the other eye, and vice versa. Participants continuously improved in a naturalistic object discrimination task over 20 one-hour sessions. Pre-training and post-training tests suggest that performance improvements were due to two learning processes: learning to recognize objects with reduced visual information and learning to suppress contrast-reversed image information in a non–eye-selective manner. These results suggest that, with training, it may be possible to adapt to the unnatural on- and off-cell population responses produced by electronic and optogenetic sight recovery technologies.

Retinal pigment epithelium 65 kDa protein (RPE65): An update

Vertebrate vision critically depends on an 11-cis-retinoid renewal system known as the visual cycle. At the heart of this metabolic pathway is an enzyme known as retinal pigment epithelium 65 kDa protein (RPE65), which catalyzes an unusual, possibly biochemically unique, reaction consisting of a coupled all-trans-retinyl ester hydrolysis and alkene geometric isomerization to produce 11-cis-retinol. Early work on this isomerohydrolase demonstrated its membership to the carotenoid cleavage dioxygenase superfamily and its essentiality for 11-cis-retinal production in the vertebrate retina. Three independent studies published in 2005 established RPE65 as the actual isomerohydrolase instead of a retinoid-binding protein as previously believed. Since the last devoted review of RPE65 enzymology appeared in this journal, major advances have been made in a number of areas including our understanding of the mechanistic details of RPE65 isomerohydrolase activity, its phylogenetic origins, the relationship of its membrane binding affinity to its catalytic activity, its role in visual chromophore production for rods and cones, its modulation by macromolecules and small molecules, and the involvement of RPE65 mutations in the development of retinal diseases. In this article, I will review these areas of progress with the goal of integrating results from the varied experimental approaches to provide a comprehensive picture of RPE65 biochemistry. Key outstanding questions that may prove to be fruitful future research pursuits will also be highlighted.

The Progression of Stargardt Disease Using Volumetric Hill of Vision Analyses Over 24 Months: ProgStar Report No.15

PURPOSE

To report the yearly rate of change in macular function in patients with Stargardt disease type 1 (STGD1) over 24 months and to establish a new volumetric visual function index for use in clinical trials investigating the efficacy on retinal sensitivity.

METHODS

Design: International, multicenter, prospective cohort study with 5 study visits every 6 months over 24 months.

PARTICIPANTS

A total of 233 individuals with genetically confirmed STGD1 (≥1 disease-causing ABCA4 variant).

MAIN OUTCOME MEASURES

The total volume (V_TOT) beneath the sensitivity surface of a 3-D model of the hill of vision and mean sensitivity (MS) derived from mesopic microperimetry performed with a white stimulus. Changes of V_TOT over time and its correlation with the ABCA4 genotype and baseline features.

RESULTS

At baseline, 440 eyes (233 patients) with a mean (SD) age of 33.7 (15.0) years, mean (SD) visual acuity of 46.08 (16.03) ETDRS letters were analyzed with an average V_TOT of 0.91 decibel-steradian (dB-sr) and an MS of 10.73 dB. The overall mean rate of decrease in sensitivity [95% confidence interval] was 0.077 [0.064, 0.090] dB-sr/y for V_TOT and 0.87 [0.72, 1.02] dB/year for MS. The progression rate of V_TOT depended on baseline visual function (0.029 dB-sr/year for low and 0.120 dB-sr/year for high baseline V_TOT; P < .001) and exhibited a difference in the first vs second year of follow-up (0.065 dB-sr/year vs 0.089 dB-sr/year, respectively; P < .001). The absence of pigmentary abnormalities of the retinal pigment epithelium at baseline was found to be associated with a faster progression rate (P < .001), whereas a significant association with the genotype was not detected (P = .7).

CONCLUSION

In STGD1, both microperimetric outcomes demonstrate statistically significant and clinically meaningful changes after relatively short follow-up periods. Volumetric modeling may be useful in future interventional clinical trials that aim to improve retinal sensitivity or to slow down its decline and for structure-function correlations.

Assessing Photoreceptor Status in Retinal Dystrophies: From High-Resolution Imaging to Functional Vision

Purpose

To describe the value of integrating phenotype/genotype data, disease staging, and evaluation of functional vision in patient-centered management of retinal dystrophies.

Methods

(1) Cross-sectional structure-function and retrospective longitudinal studies to assess the correlations between standard fundus autofluorescence (FAF), optical coherence tomography, visual acuity (VA), and perimetry (visual field [VF]) examinations to evaluate photoreceptor functional loss in a cohort of patients with rod-cone dystrophy (RCD); (2) flood-illumination adaptive optics (FIAO) imaging focusing on photoreceptor misalignment and orientation of outer segments; and (3) evaluation of the impact of visual impairment in daily life activities, based on functional (visual and mobility) vision assessment in a naturalistic environment in visually impaired subjects with RCD and subjects treated with Luxturna^Ⓡ for RPE65-related Leber congenital amaurosis before and after therapy.

Results

The results of the cross-sectional transversal study showed that (1) VA and macular sensitivity were weakly correlated with the structural variables; and (2) functional impairment (VF) was correlated with reduction of anatomical markers of photoreceptor structure and increased width of autofluorescent ring. The dimensions of the ring of increased FAF evolved faster. Other criteria that differed among groups were the lengths of the ellipsoid zone, the external limiting membrane, and the foveal thickness. FIAO revealed a variety of phenotypes: paradoxical visibility of foveal cones; heterogeneous brightness of cones; dim, inner segment–like, and RPE-like mosaic. Directional illumination by varying orientation of incident light (Stiles-Crawford effect) and the amount of side illumination (gaze-dependent imaging) affected photoreceptor visibility. Mobility assessment under different lighting conditions showed correlation with VF, VA, contrast sensitivity (CS), and dark adaptation, with different predictive values depending on mobility study paradigms and illumination level. At high illumination level (235 lux), VF was a predictor for all mobility performance models. Under low illumination (1 and 2 lux), VF was the most significant predictor of mobility performance variables, while CS best explained the number of collisions and segments. In subjects treated with Luxturna^Ⓡ, a very favorable impact on travel speed and reduction in the number of collisions, especially at low luminance, was observable 6 months following injection, in both children and adults.

Conclusions

Our results suggest the benefit of development and implementation of quantitative and reproducible tools to evaluate the status of photoreceptors and the impact of both visual impairment and novel therapies in real-life conditions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Mapping Visual Field Defects With fMRI - Impact of Approach and Experimental Conditions

Current initiatives to restore vision emphasize the need for objective assessments of visual field (VF) defects as pursued with functional magnetic resonance imaging (fMRI) approaches. Here, we compared population receptive field (pRF) mapping-based VF reconstructions to an fMRI method that uses more robust visual stimulation (on-off block design) in combination with individualized anatomy-driven retinotopic atlas-information (atlas-based VF). We investigated participants with sizable peripheral VF-deficits due to advanced glaucoma (n = 4) or retinitis pigmentosa (RP; n = 2) and controls (n = 6) with simulated scotoma. We obtained (1) standard automated perimetry (SAP) data as reference VFs and 3T fMRI data for (2) pRF-mapping [8-direction bar stimulus, fixation color change task] and (3) block-design full-field stimulation [8-direction drifting contrast patterns during (a) passive viewing (PV) and (b) one-back-task (OBT; reporting successions of identical motion directions) to probe the impact of previously reported task-related unspecific visual cortex activations]. Correspondence measures between the SAP and fMRI-based VFs were accuracy, assisted by sensitivity and specificity. We found an accuracy of pRF-based VF from V1 in patients [median: 0.62] that was similar to previous reports and increased by adding V2 and V3 to the analysis [0.74]. In comparison to the pRF-based VF, equivalent accuracies were obtained for the atlas-based VF for both PV [0.67] and, unexpectedly, the OBT [0.59], where, however, unspecific cortical activations were reflected by a reduction in sensitivity [0.71 (PV) and 0.35 (OBT)]. In conclusion, in patients with peripheral VF-defects, we demonstrate that previous fMRI procedures to obtain VF-estimates might be enhanced by: (1) pooling V1-V3 to enhance accuracy; (2) reporting sensitivity and specificity measures to increase transparency of the VF-reconstruction metric; (3) applying atlas-based procedures, if pRF-based VFs are not available or difficult to obtain; and (4) giving, counter-intuitively, preference to PV. These findings are expected to provide guidance to overcome current limitations of translating fMRI-based methods to a clinical work-up.

Inducible Pluripotent Stem Cells to Model and Treat Inherited Degenerative Diseases of the Outer Retina: 3D-Organoids Limitations and Bioengineering Solutions

Inherited retinal degenerations (IRD) affecting either photoreceptors or pigment epithelial cells cause progressive visual loss and severe disability, up to complete blindness. Retinal organoids (ROs) technologies opened up the development of human inducible pluripotent stem cells (hiPSC) for disease modeling and replacement therapies. However, hiPSC-derived ROs applications to IRD presently display limited maturation and functionality, with most photoreceptors lacking well-developed outer segments (OS) and light responsiveness comparable to their adult retinal counterparts. In this review, we address for the first time the microenvironment where OS mature, i.e., the subretinal space (SRS), and discuss SRS role in photoreceptors metabolic reprogramming required for OS generation. We also address bioengineering issues to improve culture systems proficiency to promote OS maturation in hiPSC-derived ROs. This issue is crucial, as satisfying the demanding metabolic needs of photoreceptors may unleash hiPSC-derived ROs full potential for disease modeling, drug development, and replacement therapies.

Impact of Photoreceptor Loss on Retinal Circuitry

Our sense of sight relies on photoreceptors, which transduce photons into the nervous system's electrochemical interpretation of the visual world. These precious photoreceptors can be disrupted by disease, injury, and aging. Once photoreceptors start to die, but before blindness occurs, the remaining retinal circuitry can withstand, mask, or exacerbate the photoreceptor deficit and potentially be receptive to newfound therapies for vision restoration. To maximize the retina's receptivity to therapy, one must understand the conditions that influence the state of the remaining retina. In this review, we provide an overview of the retina's structure and function in health and disease. We analyze a collection of observations on photoreceptor disruption and generate a predictive model to identify parameters that influence the retina's response. Finally, we speculate on whether the retina, with its remarkable capacity to function over light levels spanning nine orders of magnitude, uses these same adaptational mechanisms to withstand and perhaps mask photoreceptor loss.

Functional Dynamics of Deafferented Early Visual Cortex in Glaucoma

In advanced retinitis pigmentosa with retinal lesions, the lesion projection zone (LPZ) in the early visual cortex can be driven during visual tasks, while it remains unresponsive during passive viewing. We tested whether this finding translates to advanced glaucoma, a major cause of acquired blindness. During visual stimulation, 3T fMRI scans were acquired for participants with advanced glaucoma (n = 4; age range: 51–72) and compared to two reference groups, i.e., advanced retinitis pigmentosa (n = 3; age range: 46–78) and age-matched healthy controls with simulated defects (n = 7). The participants viewed grating patterns drifting in 8 directions (12 s) alternating with uniform gray (12 s), either during passive viewing (PV), i.e., central fixation, or during a one-back task (OBT), i.e., reports of succeeding identical motion directions. As another reference, a fixation-dot task condition was included. Only in glaucoma and retinitis pigmentosa but not in controls, fMRI-responses in the lesion projection zone (LPZ) of V1 shifted from negative for PV to positive for OBT (p = 0.024 and p = 0.012, respectively). In glaucoma, these effects also reached significance in V3 (p = 0.006), while in V2 there was a non-significant trend (p = 0.069). The general absence of positive responses in the LPZ during PV underscores the lack of early visual cortex bottom-up plasticity for acquired visual field defects in humans. Trends in our exploratory analysis suggesting the task-dependent LPZ responses to be inversely related to visual field loss, indicate the benefit of patient stratification strategies in future studies with greater sample sizes. We conclude that top-down mechanisms associated with task-elicited demands rather than visual cortex remapping appear to shape LPZ responses not only in retinitis pigmentosa, but also in glaucoma. These insights are of critical importance for the development of schemes for treatment and rehabilitation in glaucoma and beyond.

Theoretical analysis of optogenetic spiking with ChRmine, bReaChES and CsChrimson-expressing neurons for retinal prostheses

Objective.Optogenetics has emerged as a promising technique for neural prosthetics, especially retinal prostheses, with unprecedented spatiotemporal resolution. Newly discovered opsins with high light sensitivity and fast temporal kinetics can provide sufficient temporal resolution at safe light powers and overcome the limitations of presently used opsins. It is also important to formulate accurate mathematical models for optogenetic retinal prostheses, which can facilitate optimization of photostimulation factors to improve the performance.Approach.A detailed theoretical analysis of optogenetic excitation of model retinal ganglion neurons (RGNs) and hippocampal neurons expressed with already tested opsins for retinal prostheses, namely, ChR2, ReaChR and ChrimsonR, and also with recently discovered potent opsins CsChrimson, bReaChES and ChRmine, was carried out.Main results.Under continuous illumination, ChRmine-expressing RGNs begin to respond at very low irradiances ∼10^-4mW mm^-2, and evoke firing upto ∼280 Hz, highest among other opsin-expressing RGNs, at 10^-2mW mm^-2. Under pulsed illumination at randomized photon fluxes, ChRmine-expressing RGNs respond to changes in pulse to pulse irradiances upto four logs, although very bright pulses >10¹⁴photons mm^-2s^-1block firing in these neurons. The minimum irradiance threshold for ChRmine-expressing RGNs is lower by two orders of magnitude, whereas, the first spike latency in ChRmine-expressing RGNs is shorter by an order of magnitude, alongwith stable latency of subsequest spikes compared to others. Further, a good set of photostimulation parameters were determined to achieve high-frequency control with single spike resolution at minimal power. Although ChrimsonR enables spiking upto 100 Hz in RGNs, it requires very high irradiances. ChRmine provides control at light powers that are two orders of magnitude smaller than that required with experimentally studied opsins, while maintaining single spike temporal resolution upto 40 Hz.Significance.The present study highlights the importance of ChRmine as a potential opsin for optogenetic retinal prostheses.

Partial recovery of visual function in a blind patient after optogenetic therapy

Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases. Retinitis pigmentosa is a neurodegenerative eye disease where loss of photoreceptors can lead to complete blindness. In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding ChrimsonR with light stimulation via engineered goggles. The goggles detect local changes in light intensity and project corresponding light pulses onto the retina in real time to activate optogenetically transduced retinal ganglion cells. The patient perceived, located, counted and touched different objects using the vector-treated eye alone while wearing the goggles. During visual perception, multichannel electroencephalographic recordings revealed object-related activity above the visual cortex. The patient could not visually detect any objects before injection with or without the goggles or after injection without the goggles. This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.

Utility of red-light ultrafast optogenetic stimulation of the auditory pathway

Optogenetic stimulation of spiral ganglion neurons (SGNs) in the ear provides a future alternative to electrical stimulation used in current cochlear implants. Here, we employed fast and very fast variants of the red-light-activated channelrhodopsin (ChR) Chrimson (f-Chrimson and vf-Chrimson) to study their utility for optogenetic stimulation of SGNs in mice. The light requirements were higher for vf-Chrimson than for f-Chrimson, even when optimizing membrane expression of vf-Chrimson by adding potassium channel trafficking sequences. Optogenetic time and intensity coding by single putative SGNs were compared with coding of acoustic clicks. vf-Chrimson enabled putative SGNs to fire at near-physiological rates with good temporal precision up to 250 Hz of stimulation. The dynamic range of SGN spike rate coding upon optogenetic stimulation was narrower than for acoustic clicks but larger than reported for electrical stimulation. The dynamic range of spike timing, on the other hand, was more comparable for optogenetic and acoustic stimulation. In conclusion, f-Chrimson and vf-Chrimson are promising candidates for optogenetic stimulation of SGNs in auditory research and future cochlear implants.

Challenging Safety and Efficacy of Retinal Gene Therapies by Retinogenesis

Gene-expression programs modulated by transcription factors (TFs) mediate key developmental events. Here, we show that the synthetic transcriptional repressor (TR; ZF6-DB), designed to treat Rhodopsin-mediated autosomal dominant retinitis pigmentosa (RHO-adRP), does not perturb murine retinal development, while maintaining its ability to block Rho expression transcriptionally. To express ZF6-DB into the developing retina, we pursued two approaches, (i) the retinal delivery (somatic expression) of ZF6-DB by Adeno-associated virus (AAV) vector (AAV-ZF6-DB) gene transfer during retinogenesis and (ii) the generation of a transgenic mouse (germ-line transmission, TR-ZF6-DB). Somatic and transgenic expression of ZF6-DB during retinogenesis does not affect retinal function of wild-type mice. The P347S mouse model of RHO-adRP, subretinally injected with AAV-ZF6-DB, or crossed with TR-ZF6-DB or shows retinal morphological and functional recovery. We propose the use of developmental transitions as an effective mode to challenge the safety of retinal gene therapies operating at genome, transcriptional, and transcript levels.

[Neuro-computational approaches for objective assessment of visual function]

BACKGROUND

Retinal pathologies affect the structure and function of post-retinal visual pathways. These post-retinal alterations bear the potential to obstruct the aim of innovative retinal treatment to restore visual function.

OBJECTIVE

Current developments in the field of neuroimaging and the associated neurocomputational approaches enable a detailed assessment of this interrelationship. As a consequence, they open up the possibility to anticipate the success of treatment.

METHODS

This review article demonstrates how innovations particularly in magnetic resonance imaging (MRI)-based anatomical, functional, and diffusion imaging can guide visual pathway assessments that are relevant for ophthalmological applications.

RESULTS

Specific examples of retinal and visual pathway pathologies in the context of a detailed analysis of the visual pathway are described.

CONCLUSION

A concept is introduced of how to translate the meaningful but technically and computationally challenging neuroimaging procedures into a clinical setting in order to effectively connect these procedures to innovative treatment approaches.