Visual prostheses: the enabling technology to give sight to the blind

Quantifying visual acuity for pre-clinical testing of visual prostheses

Objective.Visual prostheses currently restore only limited vision. More research and pre-clinical work are required to improve the devices and stimulation strategies that are used to induce neural activity that results in visual perception. Evaluation of candidate strategies and devices requires an objective way to convert measured and modelled patterns of neural activity into a quantitative measure of visual acuity.Approach.This study presents an approach that compares evoked patterns of neural activation with target and reference patterns. A d-prime measure of discriminability determines whether the evoked neural activation pattern is sufficient to discriminate between the target and reference patterns and thus provides a quantified level of visual perception in the clinical Snellen and MAR scales. The magnitude of the resulting value was demonstrated using scaled standardized 'C' and 'E' optotypes.Main results.The approach was used to assess the visual acuity provided by two alternative stimulation strategies applied to simulated retinal implants with different electrode pitch configurations and differently sized spreads of neural activity. It was found that when there is substantial overlap in neural activity generated by different electrodes, an estimate of acuity based only upon electrode pitch is incorrect; our proposed method gives an accurate result in both circumstances.Significance.Quantification of visual acuity using this approach in pre-clinical development will allow for more rapid and accurate prototyping of improved devices and neural stimulation strategies.

2D Semiconductor Based Flexible Photoresponsive Ring Oscillators for Artificial Vision Pixels

Artificial retina implantation provides an effective and feasible attempt for vision recovery in addition to retinal transplantation. The most advanced artificial retinas ever developed based on silicon technology are rigid and thus less compatible with the biosystem. Here we demonstrate flexible photoresponsive ring oscillators (PROs) based on the 2D semiconductor MoS2 for artificial retinas. Under natural light illuminations, arrayed PROs on flexible substrates serving as vision pixels can efficiently output light-intensity-dependent electrical pulses that are processable and transmittable in the human visual nerve system. Such PROs can work under low supply voltages below 1 V with a record-low power consumption, e.g. only 12.4 nW at a light intensity of 10 mW/cm2, decreased by ∼500 times compared with that of the state-of-the-art silicon devices. Such flexible artificial retinas with a simple device structure, high light-to-signal conversion efficiency, ultralow power consumption, and high tunability provide an alternative prosthesis for further clinical trials.

Object recognition and localization enhancement in visual prostheses: a real-time mixed reality simulation

Blindness is a main threat that affects the daily life activities of any human. Visual prostheses have been introduced to provide artificial vision to the blind with the aim of allowing them to restore confidence and independence. In this article, we propose an approach that involves four image enhancement techniques to facilitate object recognition and localization for visual prostheses users. These techniques are clip art representation of the objects, edge sharpening, corner enhancement and electrode dropout handling. The proposed techniques are tested in a real-time mixed reality simulation environment that mimics vision perceived by visual prostheses users. Twelve experiments were conducted to measure the performance of the participants in object recognition and localization. The experiments involved single objects, multiple objects and navigation. To evaluate the performance of the participants in objects recognition, we measure their recognition time, recognition accuracy and confidence level. For object localization, two metrics were used to measure the performance of the participants which are the grasping attempt time and the grasping accuracy. The results demonstrate that using all enhancement techniques simultaneously gives higher accuracy, higher confidence level and less time for recognizing and grasping objects in comparison to not applying the enhancement techniques or applying pair-wise combinations of them. Visual prostheses could benefit from the proposed approach to provide users with an enhanced perception.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Head-mounted digital metamorphopsia suppression as a countermeasure for macular-related visual distortions for prolonged spaceflight missions and terrestrial health

During long-duration spaceflight, astronauts are exposed to various risks including spaceflight-associated neuro-ocular syndrome, which serves as a risk to astronaut vision and a potential physiological barrier to future spaceflight. When considering exploration missions that may expose astronauts to longer periods of microgravity, radiation exposure, and natural aging processes during spaceflight, more severe changes to functional vision may occur. The macula plays a critical role in central vision and disruptions to this key area in the eye may compromise functional vision and mission performance. In this article, we describe the development of a countermeasure technique to digitally suppress monocular central visual distortion with head-mounted display technology. We report early validation studies with this noninvasive countermeasure in individuals with simulated metamorphopsia. When worn by these individuals, this emerging wearable countermeasure technology has demonstrated a suppression of monocular visual distortion. We describe the considerations and further directions of this head-mounted technology for both astronauts and aging individuals on Earth.

Improving the spatial resolution of artificial vision using midget retinal ganglion cell populations modelled at the human fovea

OBJECTIVE

Retinal prostheses seek to create artificial vision by stimulating surviving retinal neurons of patients with profound vision impairment. Notwithstanding tremendous research efforts, the performance of all implants tested to date has remained rudimentary, incapable of overcoming the threshold for legal blindness. To maximize the perceptual efficacy of retinal prostheses, a device must be capable of controlling retinal neurons with greater spatiotemporal precision. Most studies of retinal stimulation were derived from either non-primate species or the peripheral primate retina. We investigated if artificial stimulation could leverage the high spatial resolution afforded by the neural substrates at the primate fovea and surrounding regions to achieve improved percept qualities.

APPROACH

We began by developing a new computational model capable of generating anatomically accurate retinal ganglion cell (RGC) populations within the human central retina. Next, multiple RGC populations across the central retina were stimulated in-silico to compare clinical and recently proposed neurostimulation configurations based on their ability to improve perceptual efficacy and reduce activation thresholds.

MAIN RESULTS

Our model uniquely upholds eccentricity-dependent characteristics such as RGC density and dendritic field diameter, whilst incorporating anatomically accurate features such as axon projection and three-dimensional RGC layering, features often forgone in favor of reduced computational complexity. Following epiretinal stimulation, the RGCs in our model produced response patterns in shapes akin to the complex percepts reported in clinical trials. Our results also demonstrated that even within the neuron-dense central retina, epiretinal stimulation using a multi-return hexapolar electrode arrangement could reliably achieve spatially focused RGC activation and could achieve single-cell excitation in 74% of all tested locations.

SIGNIFICANCE

This study establishes an anatomically accurate three-dimensional model of the human central retina and demonstrates the potential for an epiretinal hexapolar configuration to achieve consistent, spatially confined retinal responses, even within the neuron-dense foveal region. Our results promote the prospect and optimization of higher spatial resolution in future epiretinal implants.

End-to-end optimization of prosthetic vision

Neural prosthetics may provide a promising solution to restore visual perception in some forms of blindness. The restored prosthetic percept is rudimentary compared to normal vision and can be optimized with a variety of image preprocessing techniques to maximize relevant information transfer. Extracting the most useful features from a visual scene is a nontrivial task and optimal preprocessing choices strongly depend on the context. Despite rapid advancements in deep learning, research currently faces a difficult challenge in finding a general and automated preprocessing strategy that can be tailored to specific tasks or user requirements. In this paper, we present a novel deep learning approach that explicitly addresses this issue by optimizing the entire process of phosphene generation in an end-to-end fashion. The proposed model is based on a deep auto-encoder architecture and includes a highly adjustable simulation module of prosthetic vision. In computational validation experiments, we show that such an approach is able to automatically find a task-specific stimulation protocol. The results of these proof-of-principle experiments illustrate the potential of end-to-end optimization for prosthetic vision. The presented approach is highly modular and our approach could be extended to automated dynamic optimization of prosthetic vision for everyday tasks, given any specific constraints, accommodating individual requirements of the end-user.

Real-world indoor mobility with simulated prosthetic vision: The benefits and feasibility of contour-based scene simplification at different phosphene resolutions

Neuroprosthetic implants are a promising technology for restoring some form of vision in people with visual impairments via electrical neurostimulation in the visual pathway. Although an artificially generated prosthetic percept is relatively limited compared with normal vision, it may provide some elementary perception of the surroundings, re-enabling daily living functionality. For mobility in particular, various studies have investigated the benefits of visual neuroprosthetics in a simulated prosthetic vision paradigm with varying outcomes. The previous literature suggests that scene simplification via image processing, and particularly contour extraction, may potentially improve the mobility performance in a virtual environment. In the current simulation study with sighted participants, we explore both the theoretically attainable benefits of strict scene simplification in an indoor environment by controlling the environmental complexity, as well as the practically achieved improvement with a deep learning-based surface boundary detection implementation compared with traditional edge detection. A simulated electrode resolution of 26 × 26 was found to provide sufficient information for mobility in a simple environment. Our results suggest that, for a lower number of implanted electrodes, the removal of background textures and within-surface gradients may be beneficial in theory. However, the deep learning-based implementation for surface boundary detection did not improve mobility performance in the current study. Furthermore, our findings indicate that, for a greater number of electrodes, the removal of within-surface gradients and background textures may deteriorate, rather than improve, mobility. Therefore, finding a balanced amount of scene simplification requires a careful tradeoff between informativity and interpretability that may depend on the number of implanted electrodes.

New Era of Electroceuticals: Clinically Driven Smart Implantable Electronic Devices Moving towards Precision Therapy

In the name of electroceuticals, bioelectronic devices have transformed and become essential for dealing with all physiological responses. This significant advancement is attributable to its interdisciplinary nature from engineering and sciences and also the progress in micro and nanotechnologies. Undoubtedly, in the future, bioelectronics would lead in such a way that diagnosing and treating patients' diseases is more efficient. In this context, we have reviewed the current advancement of implantable medical electronics (electroceuticals) with their immense potential advantages. Specifically, the article discusses pacemakers, neural stimulation, artificial retinae, and vagus nerve stimulation, their micro/nanoscale features, and material aspects as value addition. Over the past years, most researchers have only focused on the electroceuticals metamorphically transforming from a concept to a device stage to positively impact the therapeutic outcomes. Herein, the article discusses the smart implants' development challenges and opportunities, electromagnetic field effects, and their potential consequences, which will be useful for developing a reliable and qualified smart electroceutical implant for targeted clinical use. Finally, this review article highlights the importance of wirelessly supplying the necessary power and wirelessly triggering functional electronic circuits with ultra-low power consumption and multi-functional advantages such as monitoring and treating the disease in real-time.

Modern concepts of bionic vision

Loss of vision is a pressing medical and social problem leading to profound disability, loss of ability to work, serious alterations in the psycho-emotional state, and a decline of the quality of life. When conservative or surgical treatment can not help restore vision, the use of visual prosthesis - bionic eye - can be an effective solution. This review covers the main modern approaches to the development of visual prosthetic systems. Analysis of publications revealed that there are several main approaches to visual prosthesis differing primarily by the anatomical structure targeted for stimulation in order to activate visual sensations. The most significant among them are retinal prostheses, optic nerve stimulation, and cortical visual prostheses. Currently, retinal prostheses such as ARGUS II demonstrate the most successful results, since the stimulation of the surviving neural structures of the retina is a relatively easy task, but their field of application is limited to diseases associated with pathological changes in photoreceptors. The development of cortical visual prostheses is more difficult, but in the future they may allow using more stimulation channels to obtain a more detailed visual perception. In addition, cortical visual prostheses are universal, as they do not require preservation of any structures of the visual organ, only the primary visual cortex.

Low vision rehabilitation for better quality of life in visually impaired adults

BACKGROUND

Low vision rehabilitation aims to optimise the use of residual vision after severe vision loss, but also aims to teach skills in order to improve visual functioning in daily life. Other aims include helping people to adapt to permanent vision loss and improving psychosocial functioning. These skills promote independence and active participation in society. Low vision rehabilitation should ultimately improve quality of life (QOL) for people who have visual impairment.

OBJECTIVES

To assess the effectiveness of low vision rehabilitation interventions on health-related QOL (HRQOL), vision-related QOL (VRQOL) or visual functioning and other closely related patient-reported outcomes in visually impaired adults.

SEARCH METHODS

We searched relevant electronic databases and trials registers up to 18 September 2019.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) investigating HRQOL, VRQOL and related outcomes of adults, with an irreversible visual impairment (World Health Organization criteria). We included studies that compared rehabilitation interventions with active or inactive control.

DATA COLLECTION AND ANALYSIS

We used standard methods expected by Cochrane. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 44 studies (73 reports) conducted in North America, Australia, Europe and Asia. Considering the clinical diversity of low vision rehabilitation interventions, the studies were categorised into four groups of related intervention types (and by comparator): (1) psychological therapies and/or group programmes, (2) methods of enhancing vision, (3) multidisciplinary rehabilitation programmes, (4) other programmes. Comparators were no care or waiting list as an inactive control group, usual care or other active control group. Participants included in the reported studies were mainly older adults with visual impairment or blindness, often as a result of age-related macular degeneration (AMD). Study settings were often hospitals or low vision rehabilitation services. Effects were measured at the short-term (six months or less) in most studies. Not all studies reported on funding, but those who did were supported by public or non-profit funders (N = 31), except for two studies. Compared to inactive comparators, we found very low-certainty evidence of no beneficial effects on HRQOL that was imprecisely estimated for psychological therapies and/or group programmes (SMD 0.26, 95% CI -0.28 to 0.80; participants = 183; studies = 1) and an imprecise estimate suggesting little or no effect of multidisciplinary rehabilitation programmes (SMD -0.08, 95% CI -0.37 to 0.21; participants = 183; studies = 2; I2 = 0%); no data were available for methods of enhancing vision or other programmes. Regarding VRQOL, we found low- or very low-certainty evidence of imprecisely estimated benefit with psychological therapies and/or group programmes (SMD -0.23, 95% CI -0.53 to 0.08; studies = 2; I2 = 24%) and methods of enhancing vision (SMD -0.19, 95% CI -0.54 to 0.15; participants = 262; studies = 5; I2 = 34%). Two studies using multidisciplinary rehabilitation programmes showed beneficial but inconsistent results, of which one study, which was at low risk of bias and used intensive rehabilitation, recorded a very large and significant effect (SMD: -1.64, 95% CI -2.05 to -1.24), and the other a small and uncertain effect (SMD -0.42, 95%: -0.90 to 0.07). Compared to active comparators, we found very low-certainty evidence of small or no beneficial effects on HRQOL that were imprecisely estimated with psychological therapies and/or group programmes including no difference (SMD -0.09, 95% CI -0.39 to 0.20; participants = 600; studies = 4; I2 = 67%). We also found very low-certainty evidence of small or no beneficial effects with methods of enhancing vision, that were imprecisely estimated (SMD -0.09, 95% CI -0.28 to 0.09; participants = 443; studies = 2; I2 = 0%) and multidisciplinary rehabilitation programmes (SMD -0.10, 95% CI -0.31 to 0.12; participants = 375; studies = 2; I2 = 0%). Concerning VRQOL, low-certainty evidence of small or no beneficial effects that were imprecisely estimated, was found with psychological therapies and/or group programmes (SMD -0.11, 95% CI -0.24 to 0.01; participants = 1245; studies = 7; I2 = 19%) and moderate-certainty evidence of small effects with methods of enhancing vision (SMD -0.24, 95% CI -0.40 to -0.08; participants = 660; studies = 7; I2 = 16%). No additional benefit was found with multidisciplinary rehabilitation programmes (SMD 0.01, 95% CI -0.18 to 0.20; participants = 464; studies = 3; I2 = 0%; low-certainty evidence). Among secondary outcomes, very low-certainty evidence of a significant and large, but imprecisely estimated benefit on self-efficacy or self-esteem was found for psychological therapies and/or group programmes versus waiting list or no care (SMD -0.85, 95% CI -1.48 to -0.22; participants = 456; studies = 5; I2 = 91%). In addition, very low-certainty evidence of a significant and large estimated benefit on depression was found for psychological therapies and/or group programmes versus waiting list or no care (SMD -1.23, 95% CI -2.18 to -0.28; participants = 456; studies = 5; I2 = 94%), and moderate-certainty evidence of a small benefit versus usual care (SMD -0.14, 95% CI -0.25 to -0.04; participants = 1334; studies = 9; I2 = 0%). ln the few studies in which (serious) adverse events were reported, these seemed unrelated to low vision rehabilitation.

AUTHORS' CONCLUSIONS

In this Cochrane Review, no evidence of benefit was found of diverse types of low vision rehabilitation interventions on HRQOL. We found low- and moderate-certainty evidence, respectively, of a small benefit on VRQOL in studies comparing psychological therapies or methods for enhancing vision with active comparators. The type of rehabilitation varied among studies, even within intervention groups, but benefits were detected even if compared to active control groups. Studies were conducted on adults with visual impairment mainly of older age, living in high-income countries and often having AMD. Most of the included studies on low vision rehabilitation had a short follow-up, Despite these limitations, the consistent direction of the effects in this review towards benefit justifies further research activities of better methodological quality including longer maintenance effects and costs of several types of low vision rehabilitation. Research on the working mechanisms of components of rehabilitation interventions in different settings, including low-income countries, is also needed.

Overvoltage Protection Circuits for Ultrasonically Powered Implantable Microsystems

This paper presents a novel overvoltage protection technique for ultrasonically powered microsystems. The proposed idea benefits from voltage-current characteristics of the piezoelectric harvesters, and limits the amplitude of the harvested signal by regulating the current consumption of the system. For this purpose, a low-area low-power overvoltage regulator is proposed, analyzed and simulated in transistor level in standard TSMC 0.18μm CMOS technology occupying a silicon area of 285μm². Furthermore, to avoid unnecessary power consumption of the overvoltage regulator, it is proposed to take advantage of an ultrasonic burst detection block to deactivate the regulator in the absence of ultrasonic waves. According to our simulation results, the quiescent power consumption of the proposed circuit in the presence and absence of ultrasonic waves are 37 and 3μW respectively, and the minimum phase margin of the negative feedback loop is 68 degree.

Human enhancement: Genetic engineering and evolution

Genetic engineering opens new possibilities for biomedical enhancement requiring ethical, societal and practical considerations to evaluate its implications for human biology, human evolution and our natural environment. In this Commentary, we consider human enhancement, and in particular, we explore genetic enhancement in an evolutionary context. In summarizing key open questions, we highlight the importance of acknowledging multiple effects (pleiotropy) and complex epigenetic interactions among genotype, phenotype and ecology, and the need to consider the unit of impact not only to the human body but also to human populations and their natural environment (systems biology). We also propose that a practicable distinction between ‘therapy’ and ‘enhancement’ may need to be drawn and effectively implemented in future regulations. Overall, we suggest that it is essential for ethical, philosophical and policy discussions on human enhancement to consider the empirical evidence provided by evolutionary biology, developmental biology and other disciplines.

Lay Summary: This Commentary explores genetic enhancement in an evolutionary context. We highlight the multiple effects associated with germline heritable genetic intervention, the need to consider the unit of impact to human populations and their natural environment, and propose that a practicable distinction between ‘therapy’ and ‘enhancement’ is needed.

Design of an Integrated Subretinal Implant using Cellular Neural Networks for Binary Image Generation in a 130 nm BiCMOS Process

Blindness caused by the eye diseases Retinitis-Pigmentosa and Age-Related-Macular-Degeneration leads to a degeneration of the photoreceptor layer while postsynaptic cells mostly stay intact. In this Paper a new concept for retinal implants is proposed. Instead of converting the incident light to a gray-scale picture with corresponding continuous-value stimulation levels, we here suggest to produce a binary image picture that only highlight edges in order to stimulate the retina solely at points which belong to an edge. An integrated test circuit is designed with a 130 nm BiCMOS process by using cellular neural networks for binary image generation. The circuit yields a simulated maximum rated power consumption of 2.61 mW for a 1000 information processing cells.

Validation and Safety of Visual Restoration by Ectopic Expression of Human Melanopsin in Retinal Ganglion Cells

To study whether ectopic human melanopsin (hMel) in retinal ganglion cells (RGCs) could restore the visual function in end-stage retinal degeneration, AAV2/8-CMV-hMel/FYP was injected into the intravitreal space of Royal College of Surgeons (RCS) rats. It was observed that ectopic hMel/yellow fluorescent protein (YFP) was dominantly expressed in the RGCs of the RCS rat retinae. At 30-45 days after administration of AAV2/8-CMV-hMel/FYP in RCS rats, the flash visual evoked potentials and behavioral results demonstrated that visual function was significantly improved compared to that in the control group, while no improvement in flash electroretinography was observed at this time point. To translate this potential therapeutic approach to the clinic, the safety of viral vectors in the retinae of normal macaques was then studied, and the expression profile of exogenous hMel with/without internal limiting membrane peeling was compared before viral vector administration. The data revealed that there was no significant difference in the number of RGCs containing exogenous hMel/YFP between the two groups. Whole-cell patch-clamp recordings demonstrated that the hMel/YFP-positive RGCs of the macaque retinae reacted to the intense light stimulation, generating inward currents and action potentials. This result confirms that the ectopic hMel expressed in RGCs is functional. Moreover, the introduction of AAV2/8-CMV-hMel/FYP does not cause detectable pathological effects. Thus, this study suggests that AAV2/8-CMV-hMel/FYP administration without internal limiting membrane peeling is safe and feasible for efficient transduction and provides therapeutic benefits to restore the visual function of patients suffering photoreceptor loss.

Novel Long-acting Pharmacotherapy for Exudative Age Related Macular Degeneration

Exudative age-related macular degeneration (AMD) is a major indication for the administration of intravitreal injections of anti-VEGF agents, which have been established as a very effective pharmacotherapy for this disease. However, treatment with anti-VEGF agents requires several patient visits for monitoring and treatment. Strategies for achieving a longer duration of pharmacological action are currently being developed. These include the development of longer-acting drugs, and of novel technologies to increase the duration of action of administered agents. This manuscript will review the novel drugs and technologies currently being developed for achieving a longer-action pharmacotherapy for exudative AMD.

Nonhuman Primate Studies to Advance Vision Science and Prevent Blindness

Most primate behavior is dependent on high acuity vision. Optimal visual performance in primates depends heavily upon frontally placed eyes, retinal specializations, and binocular vision. To see an object clearly its image must be placed on or near the fovea of each eye. The oculomotor system is responsible for maintaining precise eye alignment during fixation and generating eye movements to track moving targets. The visual system of nonhuman primates has a similar anatomical organization and functional capability to that of humans. This allows results obtained in nonhuman primates to be applied to humans. The visual and oculomotor systems of primates are immature at birth and sensitive to the quality of binocular visual and eye movement experience during the first months of life. Disruption of postnatal experience can lead to problems in eye alignment (strabismus), amblyopia, unsteady gaze (nystagmus), and defective eye movements. Recent studies in nonhuman primates have begun to discover the neural mechanisms associated with these conditions. In addition, genetic defects that target the retina can lead to blindness. A variety of approaches including gene therapy, stem cell treatment, neuroprosthetics, and optogenetics are currently being used to restore function associated with retinal diseases. Nonhuman primates often provide the best animal model for advancing fundamental knowledge and developing new treatments and cures for blinding diseases.

Toward the Art of Robotic-assisted Vitreoretinal Surgery

New technological progress in robotics has brought many beneficial clinical applications. Currently, computer integrated robotic surgery has gained clinical acceptance for several surgical procedures. Robotically assisted eye surgery is envisaged as a promising solution to overcome the shortcomings inherent to conventional surgical procedures as in vitreoretinal surgeries. Robotics by its high precision and fine mechanical control can improve dexterity, cancel tremor, and allow highly precise remote surgical capability, delicate vitreoretinal manipulation capabilities. Combined with magnified three-dimensional imaging of the surgical site, it can enhance surgical precision. Tele-manipulation can provide the ability for tele-surgery or haptic feedback of forces generated by the manipulation of intraocular tissues. It presents new solutions for some sight-threatening conditions such as retinal vein cannulation where, due to physiological limitations of the surgeon's hand, the procedure cannot be adequately performed. In this paper, we provide an overview of the research and advances in robotically assisted vitreoretinal eye surgery. Additionally the barriers to the integration of this method in the field of ocular surgery are summarized. Finally, we discuss the possible applications of the method in the area of vitreoretinal surgery.

Retinitis Pigmentosa: Progress and Perspective

Retinitis pigmentosa is the most common form of hereditary retinal degeneration causing blindness. Great progress has been made in the identification of the causative genes. Gene diagnosis will soon become an affordable routine clinical test because of the wide application of next-generation sequencing. Gene-based therapy provides hope for curing the disease. Investigation into the molecular pathways from mutation to rod cell death may reveal targets for developing new treatment. Related progress with existing systematic review is briefly summarized so that readers may find the relevant references for in-depth reading. Future trends in the study of retinitis pigmentosa are also discussed.

The Treatment Paradigm for the Implantable Miniature Telescope

Advanced or end-stage age-related macular degeneration (AMD) results in significant visual impairment and a substantially reduced quality of life for patients. Therapeutic options for people with bilateral moderate or profound vision loss caused by end-stage AMD are limited. Although medical treatment capable of reversing the functional vision loss that results from end-stage AMD is non-existent, there are now treatments that can reverse some of that functional vision loss, including the implantable miniature telescope (IMT). This review article discusses the science behind the IMT, evaluates the data from clinical studies, and weighs the pros and cons of the technology.

Versatile Stimulation Back-End With Programmable Exponential Current Pulse Shapes for a Retinal Visual Prosthesis

This paper reports on the design, implementation, and test of a stimulation back-end, for an implantable retinal prosthesis. In addition to traditional rectangular pulse shapes, the circuit features biphasic stimulation pulses with both rising and falling exponential shapes, whose time constants are digitally programmable. A class-B second generation current conveyor is used as a wide-swing, high-output-resistance stimulation current driver, delivering stimulation current pulses of up to ±96 μA to the target tissue. Duration of the generated current pulses is programmable within the range of 100 μs to 3 ms. Current-mode digital-to-analog converters (DACs) are used to program the amplitudes of the stimulation pulses. Fabricated using the IBM 130 nm process, the circuit consumes 1.5×1.5 mm² of silicon area. According to the measurements, the DACs exhibit DNL and INL of 0.23 LSB and 0.364 LSB, respectively. Experimental results indicate that the stimuli generator meets expected requirements when connected to electrode-tissue impedance of as high as 25 k Ω. Maximum power consumption of the proposed design is 3.4 mW when delivering biphasic rectangular pulses to the target load. A charge pump block is in charge of the upconversion of the standard 1.2-V supply voltage to ±3.3V.

Retinal Remodeling: Concerns, Emerging Remedies and Future Prospects

Deafferentation results not only in sensory loss, but also in a variety of alterations in the postsynaptic circuitry. These alterations may have detrimental impact on potential treatment strategies. Progressive loss of photoreceptors in retinal degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration, leads to several changes in the remnant retinal circuitry. Müller glial cells undergo hypertrophy and form a glial seal. The second- and third-order retinal neurons undergo morphological, biochemical and physiological alterations. A result of these alterations is that retinal ganglion cells (RGCs), the output neurons of the retina, become hyperactive and exhibit spontaneous, oscillatory bursts of spikes. This aberrant electrical activity degrades the signal-to-noise ratio in RGC responses, and thus the quality of information they transmit to the brain. These changes in the remnant retina, collectively termed “retinal remodeling”, pose challenges for genetic, cellular and bionic approaches to restore vision. It is therefore crucial to understand the nature of retinal remodeling, how it affects the ability of remnant retina to respond to novel therapeutic strategies, and how to ameliorate its effects. In this article, we discuss these topics, and suggest that the pathological state of the retinal output following photoreceptor loss is reversible, and therefore, amenable to restorative strategies.