Chromatic Full-Field Stimulus Threshold and Pupillography as Functional Markers for Late-Stage, Early-Onset Retinitis Pigmentosa Caused by CRB1 Mutations

Purpose

Mutations in the CRB1 gene cause early-onset retinal degeneration (EORD). Clinical disease progression markers, such as visual fields or electrophysiology, are not reliably measurable in most patients to follow the retinal function in patients with CRB1-mutations.

Methods

Ten patients (five females, five males; age 22–56 years) with EORD caused by CRB1 mutations were examined in a cross-sectional manner using best corrected visual acuity (BCVA), perimetry, full-field and multifocal electroretinography, full-field stimulus threshold (FST), and pupillography to red and blue light. Disease duration was defined as the difference between the age at the first symptoms to the age at examination in years.

Results

BCVA was quantifiable in six patients and ranged from light perception to 20/50. The visual field was measurable only in three patients who had the shortest disease duration. Full-field and multifocal electroretinography were not measurable in any patient. FST to blue and red light were measurable in all patients except the one with the longest disease duration; the thresholds ranged from −16.7 to 1.5 dB for red light and from −40.2 to 2.5 dB for blue light (0 dB = 0.01 cd.s/m²) and showed correlations with disease duration (r = 0.87 for blue, r = 0.65 for red, r = 0.8 for blue–red difference). The maximal relative pupil constriction amplitude (MRA) showed low or no correlations with disease duration (r = −0.55 for blue, r = −0.3 for red light); the blue–red difference in the post-illumination pupil responses (PIPR) showed no correlation with disease duration (r = −0.05). Compared to healthy eyes, the MRA to red and blue light was significantly decreased (P < 0.001) and the blue–red PIPR difference was significantly increased (P = 0.003).

Conclusions

FST features a valid clinical marker in late-stage early-onset retinitis pigmentosa caused by CRB1 mutations correlating with disease duration. This indicates the potential as a progression marker of disease. The pupil responses to full-field chromatic stimuli show significant differences from the normal population: the remaining responses, although reduced, indicate a partially preserved inner retinal function despite severe photoreceptor dysfunction.

Translational Relevance

The functional measurements presented in this study present a valid clinical progression marker in late-stage early onset retinitis pigmentosa caused by biallelic CRB1 mutations. Additionally, they can be used as outcome measures for safety and efficacy in clinical therapy trials.

An update on retinal prostheses

Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cortex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration. There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included conjunctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely. Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a complex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field.

Changes in microchip position after implantation of a subretinal vision prosthesis in humans

PURPOSE

Retinal prosthetic devices have been developed to partially restore very low vision in legally blind patients with end-stage hereditary retinal dystrophies. Subretinal implants, unlike epiretinal implants, are not fixated by a tack. The aim of this study was to assess and analyse possible changes over time in the subretinal position of the RETINA IMPLANT Alpha IMS and Alpha AMS (ClinicalTrials.gov NCT01024803).

METHODS

Imaging studies were performed on fundus photographs using GIMP (Version 2.8.14). Postoperative photographs of the implanted eye were scaled and aligned. Landmarks were chosen and distances between landmarks were measured to then calculate the displacement of the microchip using a transformation matrix for rotational and translational movements. Analyses were performed using MATLAB 8.6 (The MathWorks Inc., Natick, MA).

RESULTS

Of the 27 datasets with the Alpha IMS device, 12 (44%) remained stable without displacement of the microchip relative to the optic disc and the major blood vessels, whereas in 15 (56%), displacement occurred. The mean ± SD displacement in those 15 eyes was 0.66 ± 0.35 mm (range, 0.24-1.67 mm). Of the eight datasets with the Alpha AMS device, 1 (13%) remained stable without displacement of the microchip relative to the optic disc and the major blood vessels, whereas in 7 (87%), displacement occurred. The mean ± SD displacement in those seven eyes was 0.66 ± 0.26 mm (range, 0.32-0.97 mm). Calculated from all eyes (including those in which no displacement occurred), the mean displacement was 0.36 mm in the IMS cohort, and 0.58 mm in the AMS cohort, however, the difference was not statistically significant (p = 0.17).

CONCLUSIONS

We have shown that the position of the subretinal implant changes in the majority of the cases after implantation. While the overall mean displacement of the chip was not significantly different in either of the cohorts, the maximum displacement was smaller in the Alpha AMS cohort.

Augmented reality powers a cognitive assistant for the blind

To restore vision for the blind, several prosthetic approaches have been explored that convey raw images to the brain. So far, these schemes all suffer from a lack of bandwidth. An alternate approach would restore vision at the cognitive level, bypassing the need to convey sensory data. A wearable computer captures video and other data, extracts important scene knowledge, and conveys that to the user in compact form. Here, we implement an intuitive user interface for such a device using augmented reality: each object in the environment has a voice and communicates with the user on command. With minimal training, this system supports many aspects of visual cognition: obstacle avoidance, scene understanding, formation and recall of spatial memories, navigation. Blind subjects can traverse an unfamiliar multi-story building on their first attempt. To spur further development in this domain, we developed an open-source environment for standardized benchmarking of visual assistive devices.

Microspheres as intraocular therapeutic tools in chronic diseases of the optic nerve and retina

Pathologies affecting the optic nerve and the retina are one of the major causes of blindness. These diseases include age-related macular degeneration (AMD), diabetic retinopathy (DR) and glaucoma, among others. Also, there are genetic disorders that affect the retina causing visual impairment. The prevalence of neurodegenerative diseases of the posterior segment is increased as most of them are related with the elderly. Even with the access to different treatments, there are some challenges in managing patients suffering retinal diseases. One of them is the need for frequent interventions. Also, an unpredictable response to therapy has suggested that different pathways may be playing a role in the development of these diseases. The management of these pathologies requires the development of controlled drug delivery systems able to slow the progression of the disease without the need of frequent invasive interventions, typically related with endophthalmitis, retinal detachment, ocular hypertension, cataract, inflammation, and floaters, among other. Biodegradable microspheres are able to encapsulate low molecular weight substances and large molecules such as biotechnological products. Over the last years, a large variety of active substances has been encapsulated in microspheres with the intention of providing neuroprotection of the optic nerve and the retina. The purpose of the present review is to describe the use of microspheres in chronic neurodegenerative diseases affecting the retina and the optic nerve. The advantage of microencapsulation of low molecular weight drugs as well as therapeutic peptides and proteins to be used as neuroprotective strategy is discussed. Also, a new use of the microspheres in the development of animal models of neurodegeneration of the posterior segment is described.

Phenotypic characterization of P23H and S334ter rhodopsin transgenic rat models of inherited retinal degeneration

We produced 8 lines of transgenic (Tg) rats expressing one of two different rhodopsin mutations in albino Sprague-Dawley (SD) rats. Three lines were generated with a proline to histidine substitution at codon 23 (P23H), the most common autosomal dominant form of retinitis pigmentosa in the United States. Five lines were generated with a termination codon at position 334 (S334ter), resulting in a C-terminal truncated opsin protein lacking the last 15 amino acid residues and containing all of the phosphorylation sites involved in rhodopsin deactivation, as well as the terminal QVAPA residues important for rhodopsin deactivation and trafficking. The rates of photoreceptor (PR) degeneration in these models vary in proportion to the ratio of mutant to wild-type rhodopsin. The models have been widely studied, but many aspects of their phenotypes have not been described. Here we present a comprehensive study of the 8 Tg lines, including the time course of PR degeneration from the onset to one year of age, retinal structure by light and electron microscopy (EM), hemispheric asymmetry and gradients of rod and cone degeneration, rhodopsin content, gene dosage effect, rapid activation and invasion of the outer retina by presumptive microglia, rod outer segment disc shedding and phagocytosis by the retinal pigmented epithelium (RPE), and retinal function by the electroretinogram (ERG). The biphasic nature of PR cell death was noted, as was the lack of an injury-induced protective response in the rat models. EM analysis revealed the accumulation of submicron vesicular structures in the interphotoreceptor space during the peak period of PR outer segment degeneration in the S334ter lines. This is likely due to the elimination of the trafficking consensus domain as seen before as with other rhodopsin mutants lacking the C-terminal QVAPA. The 8 rhodopsin Tg lines have been, and will continue to be, extremely useful models for the experimental study of inherited retinal degenerations.

Optical Coherence Tomography in Patients With the Subretinal Implant Retina Implant Alpha IMS

BACKGROUND AND OBJECTIVE

The aim of this study was to assess changes in retinal structure and thickness after subretinal implantation of the Retina Implant Alpha IMS (Retina Implant AG, Reutlingen, Germany).

PATIENTS AND METHODS

Spectral-domain optical coherence tomography (SD-OCT) imaging was performed to assess the structure and thickness of the retina anterior to the microphotodiode array preoperatively, within 6 weeks and 6 months ± 1 month after implantation. Thickness measurements were performed using the distance tool of the built-in software. Three thickness measurements were performed in each of the four quadrants of the retina on the microchip within 6 weeks and 6 months ± 1 month after implantation.

RESULTS

The mean ± standard deviation change in retinal thickness from within 6 weeks to 6 months ± 1 month after implantation in all four quadrants combined was 24 μm ± 68 μm. None of the tested variables (location, time, or their interaction) had a statistically significant effect on the mean retinal thickness (P = .961, P = .131, and P = .182, respectively; n = 19).

CONCLUSION

The authors report on qualitative and quantitative findings in retinal structure in 27 patients after subretinal implantation of the Retina Implant Alpha IMS using OCT technology. No significant changes of retinal thickness could be observed in a period of 6 months after surgery. With more patients receiving subretinal implants and with advanced OCT technology, the data set will be extended to study possible changes in retinal structure in finer detail. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:993-999.].

Stochastic resonance improves vision in the severely impaired

We verified whether a stochastic resonance paradigm (SR), with random interference (“noise”) added in optimal amounts, improves the detection of sub-threshold visual information by subjects with retinal disorder and impaired vision as it does in the normally sighted. Six levels of dynamic, zero-mean Gaussian noise were added to each pixel of images (13 contrast levels) in which alphabet characters were displayed against a uniform gray background. Images were presented with contrast below the subjective threshold to 14 visually impaired subjects (age: 22–53 yrs.). The fraction of recognized letters varied between 0 and 0.3 at baseline and increased in all subjects when noise was added in optimal amounts; peak recognition ranged between 0.2 and 0.8 at noise sigmas between 6 and 30 grey scale values (GSV) and decreased in all subjects at noise levels with sigma above 30 GSV. The results replicate in the visually impaired the facilitation of visual information processing with images presented in SR paradigms that has been documented in sighted subjects. The effect was obtained with low-level image manipulation and application appears readily possible: it would enhance the efficiency of today vision-improving aids and help in the development of the visual prostheses hopefully available in the future.

Cilia - The sensory antennae in the eye

Cilia are hair-like projections found on almost all cells in the human body. Originally believed to function merely in motility, the function of solitary non-motile (primary) cilia was long overlooked. Recent research has demonstrated that primary cilia function as signalling hubs that sense environmental cues and are pivotal for organ development and function, tissue hoemoestasis, and maintenance of human health. Cilia share a common anatomy and their diverse functional features are achieved by evolutionarily conserved functional modules, organized into sub-compartments. Defects in these functional modules are responsible for a rapidly growing list of human diseases collectively termed ciliopathies. Ocular pathogenesis is common in virtually all classes of syndromic ciliopathies, and disruptions in cilia genes have been found to be causative in a growing number of non-syndromic retinal dystrophies. This review will address what is currently known about cilia contribution to visual function. We will focus on the molecular and cellular functions of ciliary proteins and their role in the photoreceptor sensory cilia and their visual phenotypes. We also highlight other ciliated cell types in tissues of the eye (e.g. lens, RPE and Müller glia cells) discussing their possible contribution to disease progression. Progress in basic research on the cilia function in the eye is paving the way for therapeutic options for retinal ciliopathies. In the final section we describe the latest advancements in gene therapy, read-through of non-sense mutations and stem cell therapy, all being adopted to treat cilia dysfunction in the retina.

Advances in implantable bionic devices for blindness: a review

Since the 1950s, vision researchers have been working towards the ambitious goal of restoring a functional level of vision to the blind via electrical stimulation of the visual pathways. Groups based in Australia, USA, Germany, France and Japan report progress in the translation of retinal visual prosthetics from the experimental to clinical domains, with two retinal visual prostheses having recently received regulatory approval for clinical use. Regulatory approval for cortical visual prostheses is yet to be obtained; however, several groups report plans to conduct clinical trials in the near future, building upon the seminal clinical studies of Brindley and Dobelle. In this review, we discuss the general principles of visual prostheses employing electrical stimulation of the visual pathways, focusing on the retina and visual cortex as the two most extensively studied stimulation sites. We also discuss the surgical and functional outcomes reported to date for retinal and cortical prostheses, concluding with a brief discussion of novel developments in this field and an outlook for the future.

Antisense Oligonucleotide Therapy for Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are an extremely heterogeneous group of genetic diseases for which currently no effective treatment strategies exist. Over the last decade, significant progress has been made utilizing gene augmentation therapy for a few genetic subtypes of IRD, although several technical challenges so far prevent a broad clinical application of this approach for other forms of IRD. Many of the mutations leading to these retinal diseases affect pre-mRNA splicing of the mutated genes . Antisense oligonucleotide (AON)-mediated splice modulation appears to be a powerful approach to correct the consequences of such mutations at the pre-mRNA level , as demonstrated by promising results in clinical trials for several inherited disorders like Duchenne muscular dystrophy, hypercholesterolemia and various types of cancer. In this mini-review, we summarize ongoing pre-clinical research on AON-based therapy for a few genetic subtypes of IRD , speculate on other potential therapeutic targets, and discuss the opportunities and challenges that lie ahead to translate splice modulation therapy for retinal disorders to the clinic.

Gliosis Can Impede Integration Following Photoreceptor Transplantation into the Diseased Retina

Retinal degenerations leading to the loss of photoreceptor (PR) cells are a major cause of vision impairment and untreatable blindness. There are few clinical treatments and none can reverse the loss of vision. With the rapid advances in stem cell biology and techniques in cell transplantation, PR replacement by transplantation represents a broad treatment strategy applicable to many types of degeneration. The number of donor cells that integrate into the recipient retina determines transplantation success, yet the degenerating retinae presents a number of barriers that can impede effective integration. Here, we briefly review recent advances in the field of PR transplantation. We then describe how different aspects of gliosis may impact on cell integration efficiency.

Pharmacological approaches to retinitis pigmentosa: A laboratory perspective

Retinal photoreceptors are highly specialized and performing neurons. Their cellular architecture is exquisitely designed to host a high concentration of molecules involved in light capture, phototransduction, electric and chemical signaling, membrane and molecular turnover, light and dark adaption, network activities etc. Such high efficiency and molecular complexity require a great metabolic demand, altogether conferring to photoreceptors particular susceptibility to external and internal insults, whose occurrence usually precipitate into degeneration of these cells and blindness. In Retinitis Pigmentosa, an impressive number of mutations in genes expressed in the retina and coding for a large varieties of proteins leads to the progressive death of photoreceptors and blindness. Recent advances in molecular tools have greatly facilitated the identification of the underlying genetics and molecular bases of RP leading to the successful implementation of gene therapy for some types of mutations, with visual restoration in human patients. Yet, genetic heterogeneity of RP makes mutation-independent approaches highly desirable, although many obstacles pave the way to general strategies for treating this complex disease, which remains orphan. The review will focus on treatments for RP based on pharmacological tools, choosing, among the many ongoing studies, approaches which rely on strong experimental evidence or rationale. For perspective treatments, new concepts are foreseen to emerge from basic studies elucidating the pathways connecting the primary mutations to photoreceptor death, possibly revealing common molecular targets for drug intervention.

Subretinal Visual Implant Alpha IMS--Clinical trial interim report

A subretinal visual implant (Alpha IMS, Retina Implant AG, Reutlingen, Germany) was implanted in 29 blind participants with outer retinal degeneration in an international multicenter clinical trial. Primary efficacy endpoints of the study protocol were a significant improvement of activities of daily living and mobility to be assessed by activities of daily living tasks, recognition tasks, mobility, or a combination thereof. Secondary efficacy endpoints were a significant improvement of visual acuity/light perception and/or object recognition (clinicaltrials.gov, NCT01024803). During up to 12 months observation time twenty-one participants (72%) reached the primary endpoints, of which thirteen participants (45%) reported restoration of visual function which they use in daily life. Additionally, detection, localization, and identification of objects were significantly better with the implant power switched on in the first 3 months. Twenty-five participants (86%) reached the secondary endpoints. Measurable grating acuity was up to 3.3 cycles per degree, visual acuities using standardized Landolt C-rings were 20/2000, 20/2000, 20/606 and 20/546. Maximal correct motion perception ranged from 3 to 35 degrees per second. These results show that subretinal implants can restore very-low-vision or low vision in blind (light perception or less) patients with end-stage hereditary retinal degenerations.

Müller glia activation in response to inherited retinal degeneration is highly varied and disease-specific

Despite different aetiologies, most inherited retinal disorders culminate in photoreceptor loss, which induces concomitant changes in the neural retina, one of the most striking being reactive gliosis by Müller cells. It is typically assumed that photoreceptor loss leads to an upregulation of glial fibrilliary acidic protein (Gfap) and other intermediate filament proteins, together with other gliosis-related changes, including loss of integrity of the outer limiting membrane (OLM) and deposition of proteoglycans. However, this is based on a mix of both injury-induced and genetic causes of photoreceptor loss. There are very few longitudinal studies of gliosis in the retina and none comparing these changes across models over time. Here, we present a comprehensive spatiotemporal assessment of features of gliosis in the degenerating murine retina that involves Müller glia. Specifically, we assessed Gfap, vimentin and chondroitin sulphate proteoglycan (CSPG) levels and outer limiting membrane (OLM) integrity over time in four murine models of inherited photoreceptor degeneration that encompass a range of disease severities (Crb1rd8/rd8, Prph2+/Δ307, Rho-/-, Pde6brd1/rd1). These features underwent very different changes, depending upon the disease-causing mutation, and that these changes are not correlated with disease severity. Intermediate filament expression did indeed increase with disease progression in Crb1rd8/rd8 and Prph2+/Δ307, but decreased in the Prph2+/Δ307 and Pde6brd1/rd1 models. CSPG deposition usually, but not always, followed the trends in intermediate filament expression. The OLM adherens junctions underwent significant remodelling in all models, but with differences in the composition of the resulting junctions; in Rho-/- mice, the adherens junctions maintained the typical rod-Müller glia interactions, while in the Pde6brd1/rd1 model they formed predominantly between Müller cells in late stage of degeneration. Together, these results show that gliosis and its associated processes are variable and disease-dependent.

Cellular strategies for retinal repair by photoreceptor replacement

Loss of photoreceptors due to retinal degeneration is a major cause of blindness in the developed world. While no effective treatment is currently available, cell replacement therapy, using pluripotent stem cell-derived photoreceptor precursor cells, may be a feasible future treatment. Recent reports have demonstrated rescue of visual function following the transplantation of immature photoreceptors and we have seen major advances in our ability to generate transplantation-competent donor cells from stem cell sources. Moreover, we are beginning to realise the possibilities of using endogenous populations of cells from within the retina itself to mediate retinal repair. Here, we present a review of our current understanding of endogenous repair mechanisms together with recent progress in the use of both ocular and pluripotent stem cells for the treatment of photoreceptor loss. We consider how our understanding of retinal development has underpinned many of the recent major advances in translation and moved us closer to the goal of restoring vision by cellular means.

First-in-human trial of a novel suprachoroidal retinal prosthesis

Retinal visual prostheses (“bionic eyes”) have the potential to restore vision to blind or profoundly vision-impaired patients. The medical bionic technology used to design, manufacture and implant such prostheses is still in its relative infancy, with various technologies and surgical approaches being evaluated. We hypothesised that a suprachoroidal implant location (between the sclera and choroid of the eye) would provide significant surgical and safety benefits for patients, allowing them to maintain preoperative residual vision as well as gaining prosthetic vision input from the device. This report details the first-in-human Phase 1 trial to investigate the use of retinal implants in the suprachoroidal space in three human subjects with end-stage retinitis pigmentosa. The success of the suprachoroidal surgical approach and its associated safety benefits, coupled with twelve-month post-operative efficacy data, holds promise for the field of vision restoration.

Trial Registration

Clinicaltrials.gov NCT01603576