Visual evoked potential in RCS rats with Okayama University-type retinal prosthesis (OUReP™) implantation

Cellular and subcellular optogenetic approaches towards neuroprotection and vision restoration

Optogenetics is defined as the combination of genetic and optical methods to induce or inhibit well-defined events in isolated cells, tissues, or animals. While optogenetics within ophthalmology has been primarily applied towards treating inherited retinal disease, there are a myriad of other applications that hold great promise for a variety of eye diseases including cellular regeneration, modulation of mitochondria and metabolism, regulation of intraocular pressure, and pain control. Supported by primary data from the authors' work with in vitro and in vivo applications, we introduce a novel approach to metabolic regulation, Opsins to Restore Cellular ATP (ORCA). We review the fundamental constructs for ophthalmic optogenetics, present current therapeutic approaches and clinical trials, and discuss the future of subcellular and signaling pathway applications for neuroprotection and vision restoration.

New epiretinal implant with integrated sensor chips for optical capturing shows a good biocompatibility profile in vitro and in vivo

BACKGROUND

Retinal degenerative diseases, e.g., retinitis pigmentosa, cause a severe decline of the visual function up to blindness. Treatment still remains difficult; however, implantation of retinal prostheses can help restoring vision. In this study, the biocompatibility and surgical feasibility of a newly developed epiretinal stimulator (OPTO-EPIRET) was investigated. The previously developed implant was extended by an integrated circuit-based optical capturing, which will enable the immediate conversion of the visual field into stimulation patterns to stimulate retinal ganglion cells.

RESULTS

The biocompatibility of the OPTO-EPIRET was investigated in vitro using the two different cell lines L-929 and R28. Direct and indirect contact were analyzed in terms of cell proliferation, cell viability, and gene expression. The surgical feasibility was initially tested by implanting the OPTO-EPIRET in cadaveric rabbit eyes. Afterwards, inactive devices were implanted in six rabbits for feasibility and biocompatibility testings in vivo. In follow-up controls (1-12 weeks post-surgery), the eyes were examined using fundoscopy and optical coherence tomography. After finalization, histological examination was performed to analyze the retinal structure. Regarding the in vitro biocompatibility, no significant influence on cell viability was detected (L929: < 1.3% dead cells; R-28: < 0.8% dead cells). The surgery, which comprised phacoemulsification, vitrectomy, and implantation of the OPTO-EPIRET through a 9-10 mm corneal incision, was successfully established. The implant was fixated with a retinal tack. Vitreal hemorrhage or retinal tearing occurred as main adverse effects. Transitional corneal edema caused difficulties in post-surgical imaging.

CONCLUSIONS

The OPTO-EPIRET stimulator showed a good biocompatibility profile in vitro. Furthermore, the implantation surgery was shown to be feasible. However, further design optimization steps are necessary to avoid intra- and postoperative complications. Overall, the OPTO-EPIRET will allow for a wide visual field and good visual acuity due to a high density of electrodes in the central retina.

Photoelectric Dye, NK-5962, as a Potential Drug for Preventing Retinal Neurons from Apoptosis: Pharmacokinetic Studies Based on Review of the Evidence

NK-5962 is a key component of photoelectric dye-based retinal prosthesis (OUReP). In testing the safety and efficacy, NK-5962 was safe in all tests for the biological evaluation of medical devices (ISO 10993) and effective in preventing retinal cells from death even under dark conditions. The long-term implantation of the photoelectric dye-coupled polyethylene film in the subretinal space of hereditary retinal dystrophic (RCS) rats prevented neurons from apoptosis in the adjacent retinal tissue. The intravitreous injection of NK-5962 in the eyes of RCS rats, indeed, reduced the number of apoptotic cells in the retinal outer nuclear layer irrespective of light or dark conditions. In this study, we reviewed the in vitro and in vivo evidence of neuroprotective effect of NK-5962 and designed pharmacokinetic experiments. The in vitro IC₅₀ of 1.7 μM, based on the protective effect on retinal cells in culture, could explain the in vivo EC₅₀ of 3 μM that is calculated from concentrations of intravitreous injection to prevent retinal neurons from apoptosis. Pharmacokinetics of NK-5962 showed that intravenous administration, but not oral administration, led to the effective concentration in the eye of rats. NK-5962 would be a candidate drug for delaying the deterioration of retinal dystrophy, such as retinitis pigmentosa.

A deep convolutional visual encoding model of neuronal responses in the LGN

The Lateral Geniculate Nucleus (LGN) represents one of the major processing sites along the visual pathway. Despite its crucial role in processing visual information and its utility as one target for recently developed visual prostheses, it is much less studied compared to the retina and the visual cortex. In this paper, we introduce a deep learning encoder to predict LGN neuronal firing in response to different visual stimulation patterns. The encoder comprises a deep Convolutional Neural Network (CNN) that incorporates visual stimulus spatiotemporal representation in addition to LGN neuronal firing history to predict the response of LGN neurons. Extracellular activity was recorded in vivo using multi-electrode arrays from single units in the LGN in 12 anesthetized rats with a total neuronal population of 150 units. Neural activity was recorded in response to single-pixel, checkerboard and geometrical shapes visual stimulation patterns. Extracted firing rates and the corresponding stimulation patterns were used to train the model. The performance of the model was assessed using different testing data sets and different firing rate windows. An overall mean correlation coefficient between the actual and the predicted firing rates of 0.57 and 0.7 was achieved for the 10 ms and the 50 ms firing rate windows, respectively. Results demonstrate that the model is robust to variability in the spatiotemporal properties of the recorded neurons outperforming other examined models including the state-of-the-art Generalized Linear Model (GLM). The results indicate the potential of deep convolutional neural networks as viable models of LGN firing.

Modelling the visual response to an OUReP retinal prosthesis with photoelectric dye coupled to polyethylene film

Objective.Retinal prostheses have been developed to restore vision in blind patients suffering from diseases like retinitis pigmentosa.Approach.A new type of retinal prosthesis called the Okayama University-type retinal prosthesis (OUReP) was developed by chemically coupling photoelectric dyes to a polyethylene film surface. The prosthesis works by passively generating an electric potential when stimulated by light. However, the neurophysiological mechanism of how OUReP stimulates the degenerated retina is unknown.Main results.Here, we explore how the OUReP affects retinal tissues using a finite element model to solve for the potential inside the tissue and an active Hodgkin-Huxley model based on rat vision to predict the corresponding retinal bipolar response.Significance.We show that the OUReP is likely capable of eliciting responses in retinal bipolar cells necessary to generate vision under most ambient conditions.

Development of highly durable retinal prosthesis using photoelectric dyes coupled to polyethylene film and quantitative in vitro evaluation of its durability

Retinal prostheses have been developed to restore vision in blind patients suffering from such diseases as retinitis pigmentosa. In our previous studies, we developed a retinal prosthesis called dye-coupled film by chemical coupling of photoelectric dyes, which absorb light and then generate electrical potential, with a polyethylene film surface. The dye-coupled film is nontoxic, and we recovered the vision of a monkey with macular degeneration. The amount of dye on the dye-coupled film, however, decreased to one-third after five months in the monkey's eye. The photoelectric dye consists of a cation with photoresponsivity and a bromide ion (Br^-). Therefore, an anion-exchange reaction could be applied to the dye-coupled film to improve its durability. In this study, the anion-exchange reaction was conducted using bis(trifluoromethanesulfonyl)imide ion (TFSI^-), which has lower nucleophilicity than Br^-. First, the long-term durability was examined without using animal subjects and in a short period. Subsequently, an elemental analysis was performed to confirm the exchange between Br^-and TFSI^-, and chemical properties, such as photoresponsivity and durability, before and after the anion exchange, were evaluated. It was quantitatively confirmed that the long-term durability of dye-coupled films can be evaluated in an in vitro environment and in a short period of one-thirtieth by utilizing a saline solution at 60°C, compared with an in vivo environment. In addition, the durability of the dye-coupled film with TFSI^-was improved to 270%-320% compared with that of the dye-coupled film with Br^-.

Vision evaluation by functional observational battery, operant behavior test, and light/dark box test in retinal dystrophic RCS rats versus normal rats

Background

Vision plays a key role in some behavior tests for rats. Okayama University-type retinal prosthesis (OUReP) is a photoelectric dye-coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. This study aims to assess vision in retinal dystrophic (RCS) rats, in comparison with normal rats, by selected behavior tests. We also examined whether the tests could detect vision changes in RCS rats with dye-coupled film implantation.

Methods

Data sets were 5 normal rats, 4 untreated RCS rats, 7 RCS rats with dye-coupled films implanted at the age of 7 weeks after excluding unsuccessful implantation at autopsy. Behavior tests chosen were landing foot splay and visual forelimb-placing response in the menu of functional observational battery, operant-conditioning lever-press response and light/dark box test.

Results

Normal visual placing response was significantly less frequent in untreated RCS rats at the age of 9 and 11 weeks, compared with normal rats (P = 0.0027, chi-square test) while normal response was significantly more frequent at the age of 9 weeks in RCS rats with dye-coupled film implantation, compared with untreated RCS rats (P = 0.0221). In operant-conditioning lever-press test, the correct response rate was significantly lower in untreated RCS rats than in normal rats at the age of 9 weeks (P < 0.05, Tukey-Kramer test) while the rate was not significantly different between normal rats and RCS rats with dye-coupled film implantation. In light/dark box test, the time to enter dark box was significantly shorter in normal rats, compared with untreated RCS rats or RCS rats with dye-coupled film implantation (P < 0.05, Tukey-Kramer test).

Conclusions

Behavior tests of functional observational battery, operant-conditioning lever-press response and light/dark box test discriminated vision between normal rats and RCS rats. The visual placing response and operant-conditioning lever-press test might have sensitivity to detect vision recovery in RCS rats with OUReP implantation.

STEM CELL THERAPIES, GENE-BASED THERAPIES, OPTOGENETICS, AND RETINAL PROSTHETICS: Current State and Implications for the Future

PURPOSE

To review and discuss current innovations and future implications of promising biotechnology and biomedical offerings in the field of retina. We focus on therapies that have already emerged as clinical offerings or are poised to do so.

METHODS

Literature review and commentary focusing on stem cell therapies, gene-based therapies, optogenetic therapies, and retinal prosthetic devices.

RESULTS

The technologies discussed herein are some of the more recent promising biotechnology and biomedical developments within the field of retina. Retinal prosthetic devices and gene-based therapies both have an FDA-approved product for ophthalmology, and many other offerings (including optogenetics) are in the pipeline. Stem cell therapies offer personalized medicine through novel regenerative mechanisms but entail complex ethical and reimbursement challenges.

CONCLUSION

Stem cell therapies, gene-based therapies, optogenetics, and retinal prosthetic devices represent a new era of biotechnological and biomedical progress. These bring new ethical, regulatory, care delivery, and reimbursement challenges. By addressing these issues proactively, we may accelerate delivery of care to patients in a safe, efficient, and value-based manner.

Long-term Rescue of Photoreceptors in a Rodent Model of Retinitis Pigmentosa Associated with MERTK Mutation

MERTK mutation reduces the ability of retinal pigment epithelial (RPE) cells to phagocytize the photoreceptor outer segments, which leads to accumulation of debris separating photoreceptors from RPE cells, resulting in their degeneration and loss of vision. In a rat model of Retinitis Pigmentosa due to MERTK mutation, we demonstrate that surgical removal of debris performed when about half of photoreceptors are lost (P38), allows the remaining photoreceptor cells to renew their outer segments and survive for at least 6 months - 3 times longer than in untreated eyes. In another set of experiments, patterned laser photocoagulation was performed before the debris formation (P19-25) to destroy a fraction of photoreceptors and thereby reduce the phagocytic load of shed outer segment fragments. This treatment also delayed the degeneration of the remaining photoreceptors. Both approaches were assessed functionally and morphologically, using electroretinography, optical coherence tomography, and histology. The long-term preservation of photoreceptors we observed indicates that MERTK-related form of inherited retinal degeneration, which has currently no cure, could be amenable to laser therapy or subretinal surgery, to extend the visual function, potentially for life.

Visual Evoked Potential Recovery by Subretinal Implantation of Photoelectric Dye-Coupled Thin Film Retinal Prosthesis in Monkey Eyes With Macular Degeneration

Retinal prosthesis or artificial retina is a promising modality of treatment for outer retinal degeneration, caused by primary and secondary loss of photoreceptor cells, in hereditary retinal dystrophy and age‐related macular degeneration, respectively. Okayama University‐type retinal prosthesis (OUReP) is a photoelectric dye‐coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. The dye‐coupled films were implanted by vitreous surgery in the subretinal space of monkey eyes with macular degeneration which had been induced by cobalt chloride injection from the scleral side. A pilot 1‐month observation study involved 6 monkeys and a pivotal 6‐month observation study involved 8 monkeys. Of 8 monkeys in 6‐month group, 3 monkeys underwent dye‐coupled film removal at 5 months and were observed further for 1 month. The amplitude of visual evoked potential which had been reduced by macular degeneration did recover at 1 month after film implantation and maintained the level at 6 months. Optical coherence tomography showed no retinal detachment, and full‐field electroretinograms maintained a‐wave and b‐wave amplitudes, indicative of no retinal toxicity. Pathological examinations after 6‐month implantation showed structural integrity of the inner retinal layer in close apposition to dye‐coupled films. The implanted films which were removed by vitrectomy 5 months later showed light‐evoked surface electric potentials by scanning Kelvin probe measurement. The photoelectric dye‐coupled film (OUReP), which serves as a light‐receiver and a displacement current generator in the subretinal space of the eye, has a potential for recovering vision in diseases with photoreceptor cell loss, such as retinitis pigmentosa and age‐related macular degeneration.

Visual evoked potential in rabbits' eyes with subretinal implantation by vitrectomy of Okayama University-type retinal prosthesis (OURePTM)

Okayama University-type retinal prosthesis (OUReP^TM) is a photoelectric dye-coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. This study aims to test surgical feasibility for subretinal film implantation and to examine functional durability of films in subretinal space. Dye-coupled films were implanted subretinally by vitrectomy in the right eye of normal white rabbits: 8 rabbits for 1 month and 8 rabbits for 6 months. The implanted films were removed by vitrectomy in 4 of these 8 rabbits in 1-month or 6-month implantation group. The films were also implanted in 4 rhodopsin-transgenic retinal dystrophic rabbits. Visual evoked potential was measured before film implantation as well as 1 or 6 months after film implantation, or 1 month after film removal. The films were successfully implanted in subretinal space of retinal detachment induced by subretinal fluid injection with a 38G polyimide tip. The retina was reattached by fluid-air exchange in vitreous cavity, retinal laser coagulation, and silicone oil injection. The ratios of P₂ amplitudes of visual evoked potential in the implanted right eye over control left eye did not show significant changes between pre-implantation and post-implantation or post-removal (paired t-test). In Kelvin probe measurements, 4 pieces each of removed films which were implanted for 1 or 6 months showed proportional increase of surface electric potential in response to increasing light intensity. The film implantation was safe and implanted films were capable of responding to light.

Subretinal implantation of Okayama University-type retinal prosthesis (OURePTM) in canine eyes by vitrectomy

Okayama University-type retinal prosthesis (OUReP^TM) is a photoelectric dye-coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. This study aims to test surgical feasibility of subretinal implantation and functional durability of dye-coupled films in the subretinal space. The dye-coupled films were implanted subretinally by 25-gauge vitrectomy in the right eye of 11 normal beagle dogs: 2 dogs served for film removal after 5-month film implantation, 3 dogs for film removal after 3-month film implantation, 3 dogs for 3-month film implantation and pathological examination, and 3 dogs for sham surgery. The surface electric potential of the removed dye-coupled films in response to light was measured by the Kelvin Probe system. At surgery, rolled-up dye-coupled films in 5 × 5 mm square size could be inserted into subretinal space of retinal detachment induced by fluid injection with a 38-gauge polyimide tip. Retinal attachment was maintained by silicone oil injection in vitreous cavity. At autopsy, the retina in all dogs maintained the ganglion cell layer, inner and outer nuclear layers while it lost the outer segments in some part. All 5 sheets of removed dye-coupled films maintained the dye color. One sheet of the 5-month implanted film showed proportional increase of surface potential in response to increasing light intensity. Subretinal implantation of OUReP^TM by vitrectomy was technically feasible in canine eyes, and OUReP^TM maintained the function of generating light-evoked surface potential after 5 months in subretinal implantation.