Retinal prostheses have been developed to fight blindness in people affected by outer retinal layer dystrophies. To date, few hundred patients have received a retinal implant. Inspired by intraocular lenses, we have designed a foldable and photovoltaic wide-field epiretinal prosthesis (named POLYRETINA) capable of stimulating wireless retinal ganglion cells. Here we show that within a visual angle of 46.3 degrees, POLYRETINA embeds 2215 stimulating pixels, of which 967 are in the central area of 5 mm, it is foldable to allow implantation through a small scleral incision, and it has a hemispherical shape to match the curvature of the eye. We demonstrate that it is not cytotoxic and respects optical and thermal safety standards; accelerated ageing shows a lifetime of at least 2 years. POLYRETINA represents significant progress towards the improvement of both visual acuity and visual field with the same device, a current challenging issue in the field.

Retinal prostheses hold the promise of restoring vision in totally blind people. However, a decade of clinical trials highlighted quantitative limitations hampering the possibility of reaching this goal. A key challenge in retinal stimulation is to independently activate retinal neurons over a large portion of the subject’s visual field. Reaching such a goal would significantly improve the perception accuracy in retinal implants’ users, along with their spatial cognition, attention, ambient mapping and interaction with the environment. Here we show a wide-field, high-density and high-resolution photovoltaic epiretinal prosthesis for artificial vision (POLYRETINA). The prosthesis embeds 10,498 physically and functionally independent photovoltaic pixels, allowing for wide retinal coverage and high-resolution stimulation. Single-pixel illumination reproducibly induced network-mediated responses from retinal ganglion cells at safe irradiance levels. Furthermore, POLYRETINA allowed response discrimination with a high spatial resolution equivalent to the pixel pitch (120 µm) thanks to the network-mediated stimulation mechanism. This approach could allow mid-peripheral artificial vision in patients with retinitis pigmentosa.

Objective. Retinal stimulation in blind patients evokes the sensation of discrete points of light called phosphenes, which allows them performing visual guided tasks, such as orientation, navigation, object recognition, object manipulation and reading. However, the clinical benefit of artificial vision in profoundly blind patients is still tenuous, as several engineering and biophysical obstacles keep it away from natural perception. The relative preservation of the inner retinal neurons in hereditary degenerative retinal diseases, such as retinitis pigmentosa, supports artificial vision through the network-mediated stimulation of retinal ganglion cells. However, the response of retinal ganglion cells to repeated electrical stimulation rapidly declines, primarily because of the intrinsic desensitisation of their excitatory network. In patients, upon repetitive stimulation, phosphenes fade out in less than half of a second, which drastically limits the understanding of the percept. Approach.A more naturalistic stimulation strategy, based on spatiotemporal modulation of electric pulses, could overcome the desensitisation of retinal ganglion cells. To investigate this hypothesis, we performed network-mediated epiretinal stimulations paired to electrophysiological recordings in retinas explanted from both male and female retinal degeneration 10 mice.Main results. The results showed that the spatial and temporal modulation of the network-mediated epiretinal stimulation prolonged the responsivity of retinal ganglion cells from 400 ms up to 4.2 s. Significance.A time-varied, non-stationary and interrupted stimulation of the retinal network, mimicking involuntary microsaccades, might reduce the fading of the visual percept and improve the clinical efficacy of retinal implants.

Organic materials, such as conjugated polymers, are attractive building blocks for bioelectronic interfaces. In particular, organic semiconductors show excellent performance in lightmediated excitation and silencing of neuronal cells and tissues. However, the main challenges of these organic photovoltaic interfaces compared to inorganic prostheses are the limited adhesion of conjugated polymers in aqueous environments and the exploitation of materials responsive in the visible spectrum. Here, we show a photovoltaic organic interface optimized for neuronal stimulation in the near-infrared spectrum. We adjusted the organic materials by chemical modification in order to improve the adhesion in an aqueous environment and to modulate the photoelectrical stimulation efficiency. As proof-of-principle, we tested this interface on explanted degenerated mice retinas, thus providing results on the efficiency and reliability of the device as an implant for neural stimulation.

Photovoltaic retinal prostheses theoretically offer the possibility of stand-alone high-resolution electrical stimulation of the retina. However, achieving focused epiretinal stimulation is particularly challenging because of axonal activation and electrical cell coupling. Recent evidence shows that long electric pulses permit a more focal activation of retinal ganglion cells, and non-rectangular waveforms induce higher network-mediated indirect activity. Objective. The role of the pulse shape in focusing the retinal ganglion cell activation and the underlying mechanisms are not yet fully understood. Approach. To address this question, we implemented a hybrid ex vivo and in silico approach. We recorded the evoked activity of retinas explanted from retinal degeneration ten mice upon photovoltaic and electrical stimulation with rectangular or non-rectangular capacitive-like voltage pulses. We used a biophysical model to investigate the role of the pulse shape and the pulse duration on the genesis and the extent of the network-mediated activity in retinal ganglion cells. Main results. Altogether, our results suggest that non-rectangular capacitive-like voltage pulses activate more strongly the inner excitatory and inhibitory layers of the retina, when compared to a rectangular stimulation with paired pulse amplitude and duration. This feature leads to an increase of the network-mediated activity and a decrease in the network-mediated electrical receptive field of the stimulated retinal ganglion cell. Significance. These results demonstrate that recruiting the inner retinal cells with epiretinal stimulation enables us not only to bypass axonal stimulation, but also to obtain a more focal activation due to the natural lateral inhibition. The involvement of the inhibitory feedback from amacrine cells in the genesis of the network-mediated activity represents a novel biological tool with which to confine the response of the retinal ganglion cells. These results support future waveform engineering strategies and offer new perspectives on epiretinal devices to better shape prosthetic perception.

Inherited retinal dystrophies (IRDs) are a large and heterogeneous group of degenerative diseases caused by mutations in various genes. Given the favorable anatomical and immunological characteristics of the eye, gene therapy holds great potential for their treatment. Our goal is to validate the preservation of visual functions by viral-free homology directed repair (HDR) in an autosomal recessive loss of function mutation. We used a tailored gene editing system based on clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to prevent retinal photoreceptor death in the retinal degeneration 10 (Rd10) mouse model of retinitis pigmentosa. We tested the gene editing tool in vitro and then used in vivo subretinal electroporation to deliver it to one of the retinas of mouse pups at different stages of photoreceptor differentiation. Three months after gene editing, the treated eye exhibited a higher visual acuity compared to the untreated eye. Moreover, we observed preservation of light-evoked responses both in explanted retinas and in the visual cortex of treated animals. Our study validates a CRISPR/Cas9-based therapy as a valuable new approach for the treatment of retinitis pigmentosa caused by autosomal recessive loss-of-function point mutations.

12 Objective. Photovoltaic retinal prostheses theoretically offer the possibility of standalone high-resolution 13 electrical stimulation of the retina. However, in artificial vision, achieving locally selective epiretinal 14 stimulation is particularly challenging, on the grounds of axonal activation and electrical cell coupling. 15 Approach. Here we show that electrical and photovoltaic stimulation of dystrophic retinal circuits with 16 capacitive-like pulses leads to a greater efficiency for indirect network-mediated activation of retinal ganglion 17 cells. In addition, a biophysical model of the inner retina stimulation is proposed to investigate the waveform 18 and duration commitments in the genesis of indirect activity of retinal ganglion cells. 19Main results. Both in-vitro and in-silico approaches suggest that the application of long voltage pulses or 20 gradual voltage changes are more effective to sustainably activate the inner excitatory and inhibitory layers of 21 the retina, thus leading to a reproducible indirect response. The involvement of the inhibitory feedback from 22 amacrine cells in the forming of indirect patterns represents a novel biological tool to locally cluster the 23 response of the retinal ganglion cells. 24Significance. These results demonstrate that recruiting inner retina cells with epiretinal stimulation enables not 25 only to bypass axonal stimulation but also to obtain a more focal activation thanks to the natural lateral 3 1. Introduction 29Retinal dystrophies, such as age-related macular degeneration and retinitis pigmentosa, are ranked among the 30 three leading causes of visual impairment worldwide (together with cataract and glaucoma) and are the primary 31 cause of visual deficit in middle income and industrialized countries, with a prevalence above 15 % [1-3]. 32Though, inner and ganglion retinal neurons are known to be temporarily spared by the degeneration process 33 and to be electrically excitable to convey artificial visual inputs to the lateral geniculate nucleus [4][5][6][7]. Several 34 retinal prostheses have been developed in the past decade and demonstrated promising results to restore an 35 elementary form of vision, including discrimination of high-contrast gratings, reading of large prints, and 36 spatial orientation [7][8][9][10][11][12][13]. Nonetheless, current clinical implants provide limited visual acuity, and the sight 37 quality is still far away from being adequate in daily life [14]. Spatial resolution keeps being one of the biggest 38 challenges (together with the wideness of the visual field) to achieve a valuable artificial vision restoration. To 39 overcome those challenges, we have designed a wireless epiretinal prosthesis (POLYRETINA) able to restore 40 a theoretical visual acuity of 20/600 and a visual field of 46 degrees, thanks to miniaturized photovoltaic pixels 41 made of organic semiconductors [15]. 42The stimulation resolution in epiretinal configuration could be improved in various complementary ways: 43 minimizing the spread of the...

Objective. Temporal resolution is a key challenge in artificial vision. Several prosthetic approaches are limited by the perceptual fading of evoked phosphenes upon repeated stimulation from the same electrode. Therefore, implanted patients are forced to perform active scanning, via head movements, to refresh the visual field viewed by the camera. However, active scanning is a draining task, and it is crucial to find compensatory strategies to reduce it. Approach. To address this question, we implemented perceptual fading in simulated prosthetic vision using virtual reality. Then, we quantified the effect of fading on two indicators: the time to complete a reading task and the head rotation during the task. We also tested if stimulation strategies previously proposed to increase the persistence of responses in retinal ganglion cells to electrical stimulation could improve these indicators. Main results. This study shows that stimulation strategies based on interrupted pulse trains and randomisation of the pulse duration allows significant reduction of both the time to complete the task and the head rotation during the task. Significance. The stimulation strategy used in retinal implants is crucial to counteract perceptual fading and to reduce active head scanning during prosthetic vision. In turn, less active scanning might improve the patient’s comfort in artificial vision.