Improvements for recording retinal function with Microelectrode Arrays.

A microelectrode array (MEA) is a configuration of multiple electrodes that enables the concurrent targeting of multiple sites for extracellular recording and stimulation. By utilizing light pulses or electrical stimulations, MEA recordings unveil the complex patterns of electrical activities that arise from the signaling processes within the retinal network. Here, we present a stepwise approach for using microelectrode arrays (MEAs) for recording action potentials from the mouse retina in response to electrical and light stimuli. We provide detailed techniques accompanied by description of a custom optical system, example recordings, troubleshooting guidelines, and data processing methods including spike sorting and code resources for analyzing light and electrical responses. The comprehensive nature of this paper aims to guide researchers in utilizing MEAs effectively for investigating retinal functionality. In particular, it can be easy to have a MEA experiment fail, but hard to identify the source of the failure. This paper is meant to demystify that process. It includes:•A description of MEA setup, recording, and spike data validation.•A troubleshooting guide for common failure modes in MEA recordings from mouse retina.•Spike detection and sorting to precisely extract distinctive action potential.

Classification of pseudocalcium visual responses from mouse retinal ganglion cells.

Recently, a detailed catalog of 32 retinal ganglion cell (RGC) visual response patterns in mouse has emerged. However, the 10,000 samples required for this catalog-based on fluorescent signals from a calcium indicator dye-are much harder to acquire from the extracellular spike train recordings underlying our bionic vision research. Therefore, we sought to convert spike trains into pseudocalcium signals so that our data could be directly matched to the 32 predefined, calcium signal-based groups. A microelectrode array (MEA) was used to record spike trains from mouse RGCs of 29 retinas. Visual stimuli were adapted from the Baden et al. study; including moving bars, full-field contrast and temporal frequency chirps, and black-white and UV-green color flashes. Spike train histograms were converted into pseudocalcium traces with an OGB-1 convolution kernel. Response features were extracted using sparse principal components analysis to match each RGC to one of the 32 RGC groups. These responses mapped onto of the 32 previously described groups; however, some of the groups remained unmatched. Thus, adaptation of the Baden et al. methodology for MEA recordings of spike trains instead of calcium recordings was partially successful. Different classification methods, however, will be needed to define clear RGC groups from MEA data for our bionic vision research. Nevertheless, others may pursue a pseudocalcium approach to reconcile spike trains with calcium signals. This work will help to guide them on the limitations and potential pitfalls of such an approach.

Retinal dystrophies with bull's-eye maculopathy along with negative ERGs.

PURPOSE: The aim of this study was to examine the ophthalmological characteristics and genotypes of patients with congenital retinal pathologies, who display a bull's-eye maculopathy in the fundus, along with a negative scotopic electroretinogram. METHODS: We analysed the results of five patients showing both a bull's-eye maculopathy, as well as a negative scotopic ERG evoked by a bright flash. Their median age was 39 years (range 11-63 years): three males and two females. All underwent a comprehensive examination with determination of distant visual acuity (ETDRS) and recording of the full-field ERG (scotopic and photopic). Fundus, OCT, and FAF images were obtained, the kinetic visual field was determined, and colour vision (D-15) was tested in most patients. Targeted gene panel sequencing was performed on peripheral blood. RESULTS: One patient carried a homozygous ABCA4 mutation and an additional heterozygous variant in CRX. Two of the five patients were shown to have a heterozygous mutation in the CRX gene, one of whom had an additional heterozygous ABCA4 mutation. Two patients had the common heterozygous mutation c.2413G>A;p.Arg838His in GUCY2D. In all of the patients, there was a reduction in the amplitude of the b-wave with a regular a-wave amplitude in the scotopic bright-flash ERG. CONCLUSIONS: The five patients with bull's-eye maculopathy along with a negative ERG had differing genotypes. Mutations were found in the CRX gene (2 patients), the ABCA4 gene (1 patient), and the GUCY2D gene (2 patients).

A case of X-linked retinoschisis with atypical fundus appearance.

PURPOSE: Mutations in the RS1 gene are known to cause retinoschisis, an X-linked hereditary retinal degeneration. Here, we present a case of atypical retinoschisis with clinical findings of retinoschisis and retinitis pigmentosa. METHODS: This report is an observational case report. The detailed ophthalmological examinations included visual field determination, multimodal imaging and electrophysiological recordings. Targeted next-generation sequencing of a retinal disease gene panel was performed. RESULTS: The 55-year-old male, highly hyperopic patient, presented with a best-corrected Snellen visual acuity of 20/100 in the right eye and 20/400 in the left eye. In the kinetic visual field, there was a superior scotoma, as well as a ring scotoma in the inferior hemisphere in the right eye and a concentric visual field constriction to 10° in the left eye. Funduscopy revealed marked pigmentary changes (i.e. bone spicules) in the mid-periphery bilaterally and symmetrically, as well as two small intra-retinal haemorrhages in the left eye. Full-field electroretinography recordings showed extinguished rod and cone responses. Diagnostic-genetic testing revealed a hemizygous missense mutation in the RS1 gene (c.305G > A; p.Arg102Gln) was identified. CONCLUSION: We present a case of atypical retinoschisis with clinical findings of retinitis pigmentosa.

Hypotrichosis with cone-rod dystrophy in a patient with cadherin 3 (CDH3) mutation.

PURPOSE: To investigate a very rare case of hypotrichosis with cone-rod dystrophy caused by a P-cadherin CDH3 mutation. METHODS: A 16-year-old Syrian girl was examined at age 9 and 14 years with an ophthalmological examination, fundus imaging, OCT and electrophysiological recordings (ERG and PERG). A disease-targeted gene panel sequencing was performed. RESULTS: Fundus images showed pigmentations at the posterior eye pole to the mid periphery, as well as vessel tortuosity. OCT images revealed a loss of the outer retinal segments and IS/OS in the central macula. The scotopic and photopic ERGs showed moderately reduced amplitudes at age 9 years that became severely reduced at age of 14 years. The PERG was undetectable at age 9 years. In color vision testing, protan-deutan confusion errors occurred. Gene panel analysis revealed one homozygous mutation in CDH3 (c.1508G>A; p.Arg503His). CONCLUSION: This case shows that a CDH3 mutation besides macula dystrophy can cause widespread cone-rod dystrophy with hypotrichosis without any other pathology besides hypoplastic nails. This points to a common pathway of hair growth and photoreceptor development that can be disturbed by a CDH3 mutation (c.1508G>A; p.Arg503His) located in the EC4 repeat region of the gene.

Spike-triggered average electrical stimuli as input filters for bionic vision-a perspective.

Bionic retinal implants are gaining acceptance in the treatment of blindness from degenerative diseases including retinitis pigmentosa and macular degeneration. OBJECTIVE: A current obstacle to the improved performance of such implants is the difficulty of comparing the results of disparate experiments. Another obstacle is the current difficulty in selectively activating the many different retinal ganglion cell types that are used as separate pathways for visual information to the brain. APPROACH: To address these obstacles, we propose a modelling framework based on white noise stimulation and reverse correlation. In this perspective, we first outline early developments in visual retinal physiology leading up to the implementation of white noise stimuli and spike-triggered averaging. We then review recent efforts to adapt the white noise method for electrical stimulation of the retina and some of the nuances of this approach. MAIN RESULTS: Based on such white noise methods, we describe a modelling framework whereby the effect of any arbitrary electrical stimulus on a ganglion cell's neural code can be better understood. SIGNIFICANCE: This framework should additionally disentangle the effects of stimulation on photoreceptor, bipolar cell and retinal ganglion cell-ultimately supporting selective stimulation of specific ganglion cell types for a more nuanced bionic retinal implant. Finally, we point to upcoming considerations in this rapidly developing domain of research.

Correspondence between visual and electrical input filters of ON and OFF mouse retinal ganglion cells.

OBJECTIVE: Over the past two decades retinal prostheses have made major strides in restoring functional vision to patients blinded by diseases such as retinitis pigmentosa. Presently, implants use single pulses to activate the retina. Though this stimulation paradigm has proved beneficial to patients, an unresolved problem is the inability to selectively stimulate the on and off visual pathways. To this end our goal was to test, using white noise, voltage-controlled, cathodic, monophasic pulse stimulation, whether different retinal ganglion cell (RGC) types in the wild type retina have different electrical input filters. This is an important precursor to addressing pathway-selective stimulation. APPROACH: Using full-field visual flash and electrical and visual Gaussian noise stimulation, combined with the technique of spike-triggered averaging (STA), we calculate the electrical and visual input filters for different types of RGCs (classified as on, off or on-off based on their response to the flash stimuli). MAIN RESULTS: Examining the STAs, we found that the spiking activity of on cells during electrical stimulation correlates with a decrease in the voltage magnitude preceding a spike, while the spiking activity of off cells correlates with an increase in the voltage preceding a spike. No electrical preference was found for on-off cells. Comparing STAs of wild type and rd10 mice revealed narrower electrical STA deflections with shorter latencies in rd10. SIGNIFICANCE: This study is the first comparison of visual cell types and their corresponding temporal electrical input filters in the retina. The altered input filters in degenerated rd10 retinas are consistent with photoreceptor stimulation underlying visual type-specific electrical STA shapes in wild type retina. It is therefore conceivable that existing implants could target partially degenerated photoreceptors that have only lost their outer segments, but not somas, to selectively activate the on and off visual pathways.

The importance of electrode position in visual electrophysiology.

PURPOSE: The DTL fibre electrode is commonly used to record the electric potentials elicited by stimulation of the retina. Two positions are commonly used: it is placed either on the cornea along the lower lid or in the conjunctival fornix. The PERG and OPs have previously been examined and compared under both conditions. The aim of this study was to examine the ERG, flicker response and on-off responses with differing electrode positions. METHODS: Before recruitment, all subjects underwent an ophthalmological examination. We enrolled 13 normal control subjects into the study aged 13-64 years, all with a visual acuity of ≥1.0. We recorded scotopic and photopic ERGs, flicker and on-off responses, for both electrode positions. On the first day, one eye had the electrode placed on the cornea along the lower lid and the other eye had it positioned in the conjunctival sac. On a second day, the recordings were repeated with the alternative electrode placements. RESULTS: ERG, on-off and flicker responses were all smaller by between 20 and 25% when the DTL electrode was positioned in the conjunctival sac, compared to when it was positioned on the cornea, as did the scatter in the data points. This indicates that there is no advantage clinically for one or the other placement. CONCLUSIONS: Our results confirm other reports examining the effect of electrode position on electrophysiological potentials. When recording with the DTL electrode, it is important to ensure that it is placed at the same position in repeat recordings or in multicentre trials and that it is stable and does not move during recording.

[Transcorneal electrical stimulation in primary open angle glaucoma]. / Transkorneale Elektrostimulation bei primärem Offenwinkelglaukom.

Recently, reports have been published on the effectiveness of electrical stimulation in patients and experimental animal models with neurodegenerative ocular diseases. Our study included 14 patients with primary open angle glaucoma (POAG), who were randomized into one of three groups with 0% (sham, n = 5), 66% (n = 5) or 150% (n = 4) of their individual electrical phosphene thresholds. Patients were treated with transcorneal electrical stimulation (TES) for 30 min once a week for 6 consecutive weeks. Outcome measures of our study were the detection of possible adverse events and efficacy of TES using DTL electrodes in subjective and objective parameters of visual function under treatment. TES was tolerated well and no serious adverse events were registered relating to the treatment. One single adverse event was registered as appearance of an optic disc hemorrhage of a sham-stimulated eye. In summary, one significant increase of intra-ocular pressure in the 66% group was observed in comparison to the sham group (p = 0.04), without significant differences compared to the 150% group (both sham vs. 150% group and 66% vs. 150% group). This difference (mean difference compared to baseline of -2.33 mm Hg for the sham group and +0.97 mm Hg for the 66% group; REML) was not clinical meaningful. All other findings, including results of the visual field, were not statistically significant different between groups. It was shown that TES using DTL electrodes did not trigger adverse or serious adverse events in the stimulated groups in patients with POAG. Patients with POAG should currently receive TES only under study conditions.

Efficacy of PARP inhibition in Pde6a mutant mouse models for retinitis pigmentosa depends on the quality and composition of individual human mutations.

Retinitis pigmentosa (RP), an inherited blinding disease, is caused by a variety of different mutations that affect retinal photoreceptor function and survival. So far there is neither effective treatment nor cure. We have previously shown that poly(ADP-ribose)polymerase (PARP) acts as a common and critical denominator of cell death in photoreceptors, qualifying it as a potential target for future therapeutic intervention. A significant fraction of RP-causing mutations affect the genes for the rod photoreceptor phosphodiesterase 6A (PDE6A) subunit, but it is not known whether they all engage the same death pathway. Analysing three homozygous point mutations (Pde6a R562W, D670G, and V685M) and one compound heterozygous Pde6a (V685M/R562W) mutation in mouse models that match human RP patients, we demonstrate excessive activation of PARP, which correlated in time with the progression of photoreceptor degeneration. The causal involvement of PARP activity in the neurodegenerative process was confirmed in organotypic retinal explant cultures treated with the PARP-selective inhibitor PJ34, using different treatment time-points and durations. Remarkably, the neuroprotective efficacy of PARP inhibition correlated inversely with the strength of the genetically induced insult, with the D670G mutant showing the best treatment effects. Our results highlight PARP as a target for neuroprotective interventions in RP caused by PDE6A mutations and are a first attempt towards personalized, genotype-matched therapy development for RP. In addition, for each of the different mutant situations, our work identifies windows of opportunity for an optimal treatment regimen for further in vivo experimentation and possibly clinical studies.

Transfer characteristics of subretinal visual implants: corneally recorded implant responses.

PURPOSE: The subretinal Alpha IMS visual implant is a CE-approved medical device for restoration of visual functions in blind patients with end-stage outer retina degeneration. We present a method to test the function of the implant objectively in vivo using standard electroretinographic equipment and to assess the devices' parameter range for an optimal perception. METHODS: Subretinal implant Alpha IMS (Retina Implant AG, Reutlingen, Germany) consists of 1500 photodiode-amplifier-electrode units and is implanted surgically into the subretinal space in blind retinitis pigmentosa patients. The voltages that regulate the amplifiers' sensitivity (V gl) and gain (V bias), related to the perception of contrast and brightness, respectively, are adjusted manually on a handheld power supply device. Corneally recorded implant responses (CRIR) to full-field illumination with long duration flashes in various implant settings for brightness gain (V bias) and amplifiers' sensitivity (V gl) are measured using electroretinographic setup with a Ganzfeld bowl in a protocol of increasing stimulus luminances up to 1000 cd/m2. RESULTS: CRIRs are a meaningful tool for assessing the transfer characteristic curves of the electronic implant in vivo monitoring the implants' voltage output as a function of log luminance in a sigmoidal shape. Changing the amplifiers' sensitivity (V gl) shifts the curve left or right along the log luminance axis. Adjustment of the gain (V bias) changes the maximal output. Contrast perception is only possible within the luminance range of the increasing slope of the function. CONCLUSIONS: The technical function of subretinal visual implants can be measured objectively using a standard electroretinographic setup. CRIRs help the patient to optimise the perception by adjusting the gain and luminance range of the device and are a useful tool for clinicians to objectively assess the function of subretinal visual implants in vivo.

Tickling the retina: integration of subthreshold electrical pulses can activate retinal neurons.

OBJECTIVE: The field of retinal prosthetics has made major progress over the last decade, restoring visual percepts to people suffering from retinitis pigmentosa. The stimulation pulses used by present implants are suprathreshold, meaning individual pulses are designed to activate the retina. In this paper we explore subthreshold pulse sequences as an alternate stimulation paradigm. Subthreshold pulses have the potential to address important open problems such as fading of visual percepts when patients are stimulated at moderate pulse repetition rates and the difficulty in preferentially stimulating different retinal pathways. APPROACH: As a first step in addressing these issues we used Gaussian white noise electrical stimulation combined with spike-triggered averaging to interrogate whether a subthreshold sequence of pulses can be used to activate the mouse retina. MAIN RESULTS: We demonstrate that the retinal network can integrate multiple subthreshold electrical stimuli under an experimental paradigm immediately relevant to retinal prostheses. Furthermore, these characteristic stimulus sequences varied in their shape and integration window length across the population of retinal ganglion cells. SIGNIFICANCE: Because the subthreshold sequences activate the retina at stimulation rates that would typically induce strong fading (25 Hz), such retinal 'tickling' has the potential to minimize the fading problem. Furthermore, the diversity found across the cell population in characteristic pulse sequences suggests that these sequences could be used to selectively address the different retinal pathways (e.g. ON versus OFF). Both of these outcomes may significantly improve visual perception in retinal implant patients.

Electrophysiology and colour: a comparison of methods to evaluate inner retinal function.

PURPOSE: Several methods are routinely used in the clinic to diagnose and monitor diseases of inner retinal function. In this study, we compare four such methods in patients with diabetes and glaucoma, to determine correlations between their results and to determine which method is most sensitive for detecting disease. METHODS: Twenty control subjects, 12 patients with early glaucoma and eight patients with diabetes mellitus, were enrolled in the study. All underwent four examinations: transient pattern electroretinogram (PERG), multifocal pattern electroretinogram (mfPERG), chromatic contrast threshold measurements (protan and tritan), and blue-on-yellow short-wavelength automated perimetry (SWAP). RESULTS: For the total cohort of 40 subjects, the results show a significant correlation between the amplitudes of the PERG and those of the mfPERG, as well as between the tritan contrast thresholds and the SWAP MD. Furthermore, ROC analyses reveal that colour contrast thresholds could significantly distinguish between the patient and the control group. Glaucoma patients alone could also be distinguished. CONCLUSIONS: We conclude that the methods compared in this study show correlations between their results if they are testing same pathway or underling cells, and that the colour contrast threshold is the most sensitive method to detect early functional deficits in diabetic and glaucoma patients.

[Ocular electrical stimulation: Therapeutic application and active retinal implants for hereditary retinal degenerations]. / Okuläre elektrische Stimulation : Therapeutische Anwendung und aktive retinale Implantate bei hereditären Netzhautdegenerationen.

BACKGROUND: Electrical stimulation has a long history in ophthalmology. Subthreshold electrical stimulation can have beneficial therapeutic effects on hereditary degenerative retinal diseases. Suprathreshold stimulation is able to elicit visual perceptions and, if multielectrode fields are arranged as an array, usable pictures can be perceived by blind patients. OBJECTIVES: This is a review article on the current situation and studies on therapeutic transcorneal electrical stimulation. Moreover, the challenges, surgical concepts and visual results of active retinal implants are discussed. MATERIAL AND METHODS: This article gives an overview on transcorneal electrical stimulation and active retinal implants based on published results, with special emphasis on the clinical application. RESULTS: The results of initial controlled studies on therapeutic transcorneal electrical stimulation in hereditary retinal diseases were very promising. The largest controlled study so far in patients with retinitis pigmentosa (RP) has yielded many positive trends and some significant improvements in electrophysiological data. Currently, two retinal implants have regulatory approval, the Argus II retinal prosthesis system® (SecondSight®) and the Alpha-IMS© (Retina Implant AG). Both systems can be used to improve visual perception and under test conditions can achieve visual acuities of 0.02 and 0.04, respectively. CONCLUSION: In-depth analyses and follow-up studies in larger patient groups are currently planned to definitively clarify the potential of therapeutic transcorneal electrical stimulation in RP patients. The challenges of currently available active retinal implants are the technical biostability and the limited spatial resolution.

Modeling the response of ON and OFF retinal bipolar cells during electric stimulation.

Retinal implants allowing blind people suffering from diseases like retinitis pigmentosa and macular degeneration to regain rudimentary vision are struggling with several obstacles. One of the main problems during external electric stimulation is the co-activation of the ON and OFF pathways which results in mutual impairment. In this study the response of ON and OFF cone retinal bipolar cells during extracellular electric stimulation from the subretinal space was examined. To gain deeper insight into the behavior of these cells sustained L-type and transient T-type calcium channels were integrated in the synaptic terminals of reconstructed 3D morphologies of ON and OFF cone bipolar cells. Intracellular calcium concentration in the synaptic regions of the model neurons was investigated as well since calcium influx is a crucial parameter for cell-to-cell activity between bipolar cells and retinal ganglion cells. It was shown that monophasic stimulation results in significant different calcium concentrations in the synaptic terminals of ON and OFF bipolar cells. Intracellular calcium increased to values up to fourfold higher in the OFF bipolar model neuron in comparison to the ON bipolar cell. Furthermore, geometric properties strongly influence the activation of bipolar cells. Monophasic, biphasic, single and repetitive pulses with similar lengths, amplitudes and polarities were applied to the two model neurons.

DNA methylation and differential gene regulation in photoreceptor cell death.

Retinitis pigmentosa (RP) defines a group of inherited degenerative retinal diseases causing progressive loss of photoreceptors. To this day, RP is still untreatable and rational treatment development will require a thorough understanding of the underlying cell death mechanisms. Methylation of the DNA base cytosine by DNA methyltransferases (DNMTs) is an important epigenetic factor regulating gene expression, cell differentiation, cell death, and survival. Previous studies suggested an involvement of epigenetic mechanisms in RP, and in this study, increased cytosine methylation was detected in dying photoreceptors in the rd1, rd2, P23H, and S334ter rodent models for RP. Ultrastructural analysis of photoreceptor nuclear morphology in the rd1 mouse model for RP revealed a severely altered chromatin structure during retinal degeneration that coincided with an increased expression of the DNMT isozyme DNMT3a. To identify disease-specific differentially methylated DNA regions (DMRs) on a genomic level, we immunoprecipitated methylated DNA fragments and subsequently analyzed them with a targeted microarray. Genome-wide comparison of DMRs between rd1 and wild-type retina revealed hypermethylation of genes involved in cell death and survival as well as cell morphology and nervous system development. When correlating DMRs with gene expression data, we found that hypermethylation occurred alongside transcriptional repression. Consistently, motif analysis showed that binding sites of several important transcription factors for retinal physiology were hypermethylated in the mutant model, which also correlated with transcriptional silencing of their respective target genes. Finally, inhibition of DNMTs in rd1 organotypic retinal explants using decitabine resulted in a substantial reduction of photoreceptor cell death, suggesting inhibition of DNA methylation as a potential novel treatment in RP.

[Personalized molecular medicine: new paradigms in the treatment of cochlear implant and cancer patients]. / Molekulare personalisierte Medizin: Paradigmenwechsel in der Krankenversorgung von Cochlear-Implant- und Tumorpatienten.

OBJECTIVES: To evaluate present options for the indication of cochlear implants (CI) and new forms of treatment for head and neck cancer, melanomas and basal cell carcinomas, with emphasis on future perspectives. METHODS: A literature search was performed in the PubMed database. Search parameters were "personalized medicine", "individualized medicine" and "molecular medicine". RESULTS: Personalized medicine based on molecular-genetic evaluation of functional proteins such as otoferlin, connexin 26 and KCNQ4 or the Usher gene is becoming increasingly important for the indication of CI in the context of infant deafness. Determination of HER2/EGFR mutations in the epithelial growth factor receptor (EGFR) gene may be an important prognostic parameter for therapeutic decisions in head and neck cancer patients. In basal cell carcinoma therapy, mutations in the Hedgehog (PCTH1) and Smoothened (SMO) pathways strongly influence the indication of therapeutic Hedgehog inhibition, e.g. using small molecules. Analyses of c-Kit receptor, BRAF-600E and NRAS mutations are required for specific molecular therapy of metastasizing melanomas. The significant advances in the field of specific molecular therapy are best illustrated by the availability of the first gene therapeutic procedures for treatment of RPE65-induced infantile retinal degradation. CONCLUSION: The aim of personalized molecular medicine is to identify patients who will respond particularly positively or negatively (e.g. in terms of adverse side effects) to a therapy using the methods of molecular medicine. This should allow a specific therapy to be successfully applied or preclude its indication in order to avoid serious adverse side effects. This approach serves to stratify patients for adequate treatment.

Novel in situ activity assays for the quantitative molecular analysis of neurodegenerative processes in the retina.

The mechanisms of neuronal cell death are still only poorly understood, which has hindered the advancement of therapies for many currently untreatable neurodegenerative diseases. This calls for the development of new methods which reveal critical molecular mechanisms of the celldeath machinery with both high sensitivity and cellular resolution. Using animal models for hereditary neurodegeneration in the retina, we have developed or adapted different biochemical assays to determine the enzymatic activities of calpain, poly-ADP-ribose-polymerase (PARP), and histone deacetylase (HDAC) directly and in situ. Additionally, the enzymatic activity of cGMP-dependent protein kinase (PKG) was assessed indirectly using in situ immunohistological techniques to detect PKG-activity-dependent products. Combining these assays with in situ cell death markers revealed close temporospatial correlations, suggesting causal connections between the PKG, HDAC, PARP and calpain activities and neuronal cell death. Using different pharmacological and genetic manipulations, causality could indeed be demonstrated. Surprisingly, the often dramatic rises in metabolic activities didnot match by corresponding increases in expression, highlighting the importance of analyses of protein activities at the cellular level. The above mentioned studies identified a number of metabolic processes previously unknownto be involved in inherited retinal degeneration. Comparing different animal retinal degeneration models uncovered striking similarities in enzymatic activities, suggesting a generality of the destructive pathways. Taken together, these findings provided a number of novel targets for neuroprotection and as such opened up new perspectives for the therapy of hereditary neurodegeneration in the retina and possibly other parts of the central nervous system.

Electronic approaches to restitute vision in patients with neurodegenerative diseases of the retina.

Degenerations of the outer retina are hereditary diseases leading to significant loss of vision. Several concepts of active electrical stimulation of the remaining retinal network resulted in the development of retinal visual implants and prosthetic vision. Subretinal and epiretinal visual implants are currently the leading approaches in restoring functional vision in blind humans with retinitis pigmentosa or other outer retinal degenerations. This review gives a short overview about the principles, advantages, limitations and vision outcome of the up-to-date published artificial vision by electronic visual implants, as well as their known biocompatibility and safety issues.