Rescue of cone and rod photoreceptor function in a CDHR1-model of age-related retinal degeneration.

Age-related macular degeneration (AMD) is the most common cause of untreatable blindness in the developed world. Recently, CDHR1 has been identified as the cause of a subset of AMD that has the appearance of the "dry" form, or geographic atrophy. Biallelic variants in CDHR1-a specialized protocadherin highly expressed in cone and rod photoreceptors-result in blindness from shortened photoreceptor outer segments and progressive photoreceptor cell death. Here we demonstrate long-term morphological, ultrastructural, functional, and behavioral rescue following CDHR1 gene therapy in a relevant murine model, sustained to 23-months after injection. This represents the first demonstration of rescue of a monogenic cadherinopathy in vivo. Moreover, the durability of CDHR1 gene therapy seems to be near complete-with morphological findings of the rescued retina not obviously different from wildtype throughout the lifespan of the mouse model. A follow-on clinical trial in patients with CDHR1-associated retinal degeneration is warranted. Hypomorphic CDHR1 variants may mimic advanced dry AMD. Accurate clinical classification is now critical, as their pathogenesis and treatment are distinct.

A Prospective, Observational, Noninterventional Clinical Study of Participants With Choroideremia: The NIGHT Study.

PURPOSE: The NIGHT study aimed to assess the natural history of choroideremia (CHM), an X-linked inherited chorioretinal degenerative disease leading to blindness, and determine which outcomes would be the most sensitive for monitoring disease progression. DESIGN: A prospective, observational, multicenter cohort study. METHODS: Males aged ≥18 years with genetically confirmed CHM, visible active disease within the macular region, and best-corrected visual acuity (BCVA) ≥34 Early Treatment Diabetic Retinopathy Study (ETDRS) letters at baseline were assessed for 20 months. The primary outcome was the change in BCVA over time at Months 4, 8, 12, 16, and 20. A range of functional and anatomical secondary outcome measures were assessed up to Month 12, including retinal sensitivity, central ellipsoid zone (EZ) area, and total area of fundus autofluorescence (FAF). Additional ocular assessments for safety were performed. RESULTS: A total of 220 participants completed the study. The mean BCVA was stable over 20 months. Most participants (81.4% in the worse eye and 77.8% in the better eye) had change from baseline > -5 ETDRS letters at Month 20. Interocular symmetry was low overall. Reductions from baseline to Month 12 were observed (worse eye, better eye) for retinal sensitivity (functional outcome; -0.68 dB, -0.48 dB), central EZ area (anatomical outcome; -0.276 mm2, -0.290 mm2), and total area of FAF (anatomical outcome; -0.605 mm2, -0.533 mm2). No assessment-related serious adverse events occurred. CONCLUSIONS: Retinal sensitivity, central EZ area, and total area of FAF are more sensitive than BCVA in measuring the natural progression of CHM.

CRISPR Manipulation of Age-Related Macular Degeneration Haplotypes in the Complement System: Potential Future Therapeutic Applications/Avenues.

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss among the elderly in the developed world. Whilst AMD is a multifactorial disease, the involvement of the complement system in its pathology is well documented, with single-nucleotide polymorphisms (SNPs) in different complement genes representing an increased risk factor. With several complement inhibitors explored in clinical trials showing limited success, patients with AMD are still without a reliable treatment option. This indicates that there is still a gap of knowledge in the functional implications and manipulation of the complement system in AMD, hindering the progress towards translational treatments. Since the discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool, the field of molecular biology has been revolutionised. Genetic variants in the complement system have long been associated with an increased risk of AMD, and a variety of haplotypes have been identified to be predisposing/protective, with variation in complement genes believed to be the trigger for dysregulation of the cascade leading to inflammation. AMD-haplotypes (SNPs) alter specific aspects of the activation and regulation of the complement cascade, providing valuable insights into the pathogenic mechanisms of AMD with important diagnostic and therapeutic implications. The effect of targeting these AMD-related SNPs on the regulation of the complement cascade has been poorly explored, and the CRISPR/Cas system provides an ideal tool with which to explore this avenue. Current research concentrates on the association events of specific AMD-related SNPs in complement genes without looking into the effect of targeting these SNPs and therefore influencing the complement system in AMD pathogenesis. This review will explore the current understanding of manipulating the complement system in AMD pathogenesis utilising the genomic manipulation powers of the CRISPR/Cas systems. A number of AMD-related SNPs in different complement factor genes will be explored, with a particular emphasis on factor H (CFH), factor B (CFB), and complement C3 (C3).

Assessment of Visual Function with Cotoretigene Toliparvovec in X-Linked Retinitis Pigmentosa in the Randomized XIRIUS Phase 2/3 Study.

PURPOSE: Cotoretigene toliparvovec (BIIB112/AAV8-RPGR) is an investigational vector-based gene therapy designed to provide a full-length, codon-optimized retinitis pigmentosa GTPase regulator (RPGR) protein to individuals with RPGR-associated X-linked retinitis pigmentosa (XLRP). We assessed efficacy and tolerability of cotoretigene toliparvovec subretinal gene therapy. DESIGN: Part 2 of the XIRIUS trial (ClinicalTrials.gov identifier, NCT03116113) was a phase 2/3, 12-month, randomized (1:1:1) dose-expansion study. PARTICIPANTS: Male patients ≥10 years of age with RPGR-associated XLRP were included. METHODS: Participants were randomized 1:1:1 to receive low-dose subretinal cotoretigene toliparvovec (5 × 1010 vector genomes/eye), high-dose cotoretigene toliparvovec (2.5 × 1011 vector genomes/eye) or to be an untreated control participant. MAIN OUTCOME MEASURES: The primary end point was the percentage of participants meeting microperimetry responder criteria (≥ 7-dB improvement at ≥ 5 of 16 central loci). Secondary end points included change from baseline in retinal sensitivity at the central 16 loci and the entire 68 loci at 12 months and change from baseline in low-luminance visual acuity (LLVA) at 12 months, as well as the proportion of eyes with a ≥ 15-Early Treatment Diabetic Retinopathy Study ETDRS letter LLVA and ≥ 10-ETDRS letter LLVA change from baseline at month 12. RESULTS: Because of the impact of the COVID-19 pandemic, enrollment ended before reaching the initial target, leaving the trial underpowered. Twenty-nine participants were included (low-dose group, n = 10; high-dose group, n = 10; control group, n = 9). At month 12, the percentage of participants meeting microperimetry responder criteria was not significantly different between either cotoretigene toliparvovec group (low dose, 37.5% [P = 0.3181]; high dose, 25.0% [P = 0.5177]) and the control group (22.2%). However, the mean change from baseline in microperimetry sensitivity improved significantly with the low-dose group versus the control group at month 12 (P = 0.0350). Significant improvement in LLVA occurred in the low-dose group versus the control group at month 12 (33.3% difference [80% confidence interval, 14.7%-55.2%]; P = 0.0498). Three ocular-related serious adverse events (SAEs) occurred in the low-dose group versus 7 SAEs in the high-dose group. CONCLUSIONS: The primary microperimetry end point was not met. Significant improvements in LLVA and mean microperimetry were observed compared with controls and fewer SAEs occured with low-dose compared with high dose cotoretigene toliparvovec. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A hypomorphic variant of choroideremia is associated with a novel intronic mutation that leads to exon skipping.

INTRODUCTION: Molecular confirmation of pathogenic sequence variants in the CHM gene is required prior to enrolment in retinal gene therapy clinical trials for choroideremia. Individuals with mild choroideremia have been reported. The molecular basis of genotype-phenotype associations is of clinical relevance since it may impact on selection for retinal gene therapy. METHODS AND MATERIALS: Genetic testing and RNA analysis were undertaken in a patient with mild choroideremia to confirm the pathogenicity of a novel intronic variant in CHM and to explore the mechanism underlying the mild clinical phenotype. RESULTS: A 42-year-old male presented with visual field loss. Fundoscopy and autofluorescence imaging demonstrated mild choroideremia for his age. Genetic analysis revealed a variant at a splice acceptor site in the CHM gene (c.1350-3C > G). RNA analysis demonstrated two out-of-frame transcripts, suggesting pathogenicity, without any detectable wildtype transcripts. One of the two out-of-frame transcripts is present in very low levels in healthy controls. DISCUSSION: Mild choroideremia may result from +3 or -3 splice site variants in CHM. It is presumed that the resulting mRNA transcripts may be partly functional, thereby preventing the development of the null phenotype. Choroideremia patients with such variants may present challenges for gene therapy since there may be residual transcript activity which could result in long-lasting visual function which is atypical for this disease.

IMPG2-Related Maculopathy.

PURPOSE: To investigate the phenotype, variability, and penetrance of IMPG2-related maculopathy. DESIGN: Retrospective observational case series. METHODS: Clinical evaluation, multimodal retinal imaging, genetic testing, and molecular modeling. RESULTS: A total of 25 individuals with a mono-allelic IMPG2 variant were included, 5 of whom were relatives of patients with IMPG2-associated retinitis pigmentosa. A distinct maculopathy was present in 17 individuals (median age, 52 years; range, 20-72 years), and included foveal elevation with or without subretinal vitelliform material or focal atrophy of the retinal pigment epithelium. Best-corrected visual acuity (BCVA) was ≥20/50 in the better eye (n = 15), and 5 patients were asymptomatic. Longitudinal observation (n = 8, up to 19 years) demonstrated stable maculopathy (n = 3), partial/complete resorption (n = 4) or increase (n = 1) of the subretinal material, with overall stable vision (n = 6). No manifest maculopathy was observed in 8 individuals (median age, 58 years; range, 43-83 years; BCVA ≥20/25), all were identified through segregation analysis. All 8 individuals were asymptomatic, with minimal foveal changes observed on optical coherence tomography in 3 cases. A total of 18 different variants were detected, 11 of them truncating. Molecular modeling of 5 missense variants [c.727G>C, c.1124C>A, c.2816T>A, c.3047T>C, and c.3193G>A] supported the hypothesis that these have a loss-of-function effect. CONCLUSIONS: Mono-allelic IMPG2 variants may result in haploinsufficiency manifesting as a maculopathy with variable penetrance and expressivity. Family members of patients with IMPG2-related retinitis pigmentosa may present with vitelliform lesions. The maculopathy often remains limited to the fovea and is usually associated with moderate visual impairment.

Hypomorphic CDHR1 variants may result in retinitis pigmentosa with relative preservation of cone function.

PURPOSE: Retinitis pigmentosa (RP) associated with biallelic variants in CDHR1 has rarely been reported, and detailed phenotyping data are not available. RP implies relative preservation of foveal cones, when compared to cone-rod dystrophy associated with biallelic null variants in CDHR1. We hypothesize that RP may occur in association with one or more hypomorphic CDHR1 alleles. MATERIALS AND METHODS: Retrospective report of a 48-year-old patient with CDHR1-associated RP with a hypomorphic missense variant c.562 G>A, p. (Gly188Ser) and a novel, unreported variant affecting a canonical splice acceptor site (c.784-1 G>C). Clinical examination, multimodal retinal imaging, electroretinography, visual field testing, and mesopic microperimetry were undertaken 8 years apart. Scotopic microperimetry was also performed. The DNA sequence context of the variants was examined to identify theoretical CRISPR-Cas9 base-editing strategies. RESULTS: The patient presented at 35 years with a 12-year history of nyctalopia. His best corrected visual acuity was 20/20. Clinical presentation, multimodal retinal imaging studies, electroretinography, and mesopic microperimetry were typical of a progressive rod-cone dystrophy (i.e. classic RP). There were no scotomas within the central field as would be expected at this age in CDHR1-associated cone-rod dystrophy. Scotopic microperimetry suggested some preservation of macular cone over rod function, although both were severely impaired. A suitable CRISPR adenine base editor was identified that could theoretically correct the missense variant c.562 G>A, p. (Gly188Ser). CONCLUSIONS: CDHR1-associated RP shows a relative preservation of cone function in the presence of a presumed hypomorphic allele and may be considered a hypomorphic disease phenotype. Further work is required to identify modifying factors that determine disease phenotype since macular dystrophy, with relative sparing of rods, may also occur with hypomorphic CDHR1 alleles.

Optical Coherence Tomography Feature of Retinoschisis in CRB1-Associated Maculopathy.

This case report describes 2 individuals with hyperreflective columns in the outer nuclear layer observed on optical coherence tomography and possible implications for CRB1-associated maculopathy.

Comment on Di Giosaffatte et al. A Novel Hypothesis on Choroideremia-Manifesting Female Carriers: Could CHM In-Frame Variants Exert a Dominant Negative Effect? A Case Report. Genes 2022, 13, 1268.

The recent publication of Di Giosaffatte et al. [...].

Outcomes and Adverse Effects of Voretigene Neparvovec Treatment for Biallelic RPE65-Mediated Inherited Retinal Dystrophies in a Cohort of Patients from a Single Center.

Our study evaluated the morphological and functional outcomes, and the side effects, of voretigene neparvovec (VN) gene therapy for RPE65-mediated inherited retinal dystrophies (IRDs) in 12 eyes (six patients) at the Oxford Eye Hospital with a mean follow-up duration of 8.2 (range 1-12) months. All patients reported a subjective vision improvement 1 month after gene therapy. Best-corrected visual acuity (BCVA) remained stable (baseline: 1.28 (±0.71) vs. last follow-up: 1.46 (±0.60); p = 0.25). Average white Full-Field Stimulus Testing (FST) showed a trend towards improvement (baseline: -4.41 (±10.62) dB vs. last follow-up: -11.98 (±13.83) dB; p = 0.18). No changes in central retinal thickness or macular volume were observed. The side effects included mild intraocular inflammation (two eyes) and cataracts (four eyes). Retinal atrophy occurred in 10 eyes (eight mild, two severe) but did not impact FST measurements during the follow-up period. Increased intraocular pressure (IOP) was noted in three patients (six eyes); four eyes (two patients) required glaucoma surgery. The overall safety and effectiveness of VN treatment in our cohort align with previous VN clinical trials, except for the higher occurrence of retinal atrophy and increased IOP in our cohort. This suggests that raised IOP and retinal atrophy may be more common than previously reported.

Subretinal timrepigene emparvovec in adult men with choroideremia: a randomized phase 3 trial.

Choroideremia is a rare, X-linked retinal degeneration resulting in progressive vision loss. A randomized, masked, phase 3 clinical trial evaluated the safety and efficacy over 12 months of follow-up in adult males with choroideremia randomized to receive a high-dose (1.0 × 1011 vector genomes (vg); n = 69) or low-dose (1.0 × 1010 vg; n = 34) subretinal injection of the AAV2-vector-based gene therapy timrepigene emparvovec versus non-treated control (n = 66). Most treatment-emergent adverse events were mild or moderate. The trial did not meet its primary endpoint of best-corrected visual acuity (BCVA) improvement. In the primary endpoint analysis, three of 65 participants (5%) in the high-dose group, one of 34 (3%) participants in the low-dose group and zero of 62 (0%) participants in the control group had ≥15-letter Early Treatment Diabetic Retinopathy Study (ETDRS) improvement from baseline BCVA at 12 months (high dose, P = 0.245 versus control; low dose, P = 0.354 versus control). As the primary endpoint was not met, key secondary endpoints were not tested for significance. In a key secondary endpoint, nine of 65 (14%), six of 35 (18%) and one of 62 (2%) participants in the high-dose, low-dose and control groups, respectively, experienced ≥10-letter ETDRS improvement from baseline BCVA at 12 months. Potential opportunities to enhance future gene therapy studies for choroideremia include optimization of entry criteria (more preserved retinal area), surgical techniques and clinical endpoints. EudraCT registration: 2015-003958-41 .

Clinical Research on the Leading Causes of Severe Sight Impairment in the UK General and Working Populations.

Purpose: Clinical research brings the potential of improved diagnostics, sight-saving treatments, and more accessible services to those suffering with severe sight impairment (SSI). This report investigates whether registered ophthalmology clinical studies address the leading causes of SSI in the general and working populations of the United Kingdom (UK). Methods: The latest statistics on the leading causes of SSI in the UK general and working populations were identified by searching PubMed, Cochrane Library, and TRIP databases. Clinical study registries were searched to identify registered clinical studies (on or prior to 1st December 2022) on the leading causes of SSI. The relationship between the number of clinical studies on leading causes of SSI and the percentage of SSI certifications they account for was analyzed. Results: In the UK general population, the number of registered clinical studies on the leading causes of SSI is statistically significantly correlated (Spearman's rho = 0.86, p < 0.01) with the percentage of SSI certifications they account for. However, there is no correlation between the two in the UK working population (aged 16-64) (Spearman's rho = 0.15, p = 0.70). Eye conditions accounting for the most SSI certifications in individuals of working age have significantly less clinical research activity than those that cause the most SSI certifications in the general population. Out of the leading causes of SSI certifications studied, disorders of the visual cortex and congenital anomalies of the eye have the least clinical research activity. Conclusion: Clinical research into the leading causes of SSI in the general population is essential. However, it is important to consider eye conditions that cause the most severe visual impairment in individuals of working age due to the significant health and socioeconomic implications of sight loss in this population.

Choroideremia: The Endpoint Endgame.

Choroideremia is an X-linked retinal degeneration resulting from the progressive, centripetal loss of photoreceptors and choriocapillaris, secondary to the degeneration of the retinal pigment epithelium. Affected individuals present in late childhood or early teenage years with nyctalopia and progressive peripheral visual loss. Typically, by the fourth decade, the macula and fovea also degenerate, resulting in advanced sight loss. Currently, there are no approved treatments for this condition. Gene therapy offers the most promising therapeutic modality for halting or regressing functional loss. The aims of the current review are to highlight the lessons learnt from clinical trials in choroideremia, review endpoints, and propose a future strategy for clinical trials.

Correlation Between Fundus Autofluorescence Pattern and Retinal Function on Microperimetry in Choroideremia.

Purpose: In patients with choroideremia, it is not known how smooth and mottled patterns on short-wavelength fundus autofluorescence (AF) imaging relate to retinal function. Methods: A retrospective case-note review was undertaken on 190 patients with choroideremia at two specialist centers for retinal genetics. Twenty patients with both smooth and mottled zones on short-wavelength AF imaging and concurrent mesopic microperimetry assessments were included. Mean retinal sensitivities within the smooth and mottled zones were compared between choroideremia patients, and identical points on mesopic microperimetry collected from 12 age-matched controls. Longitudinal analyses were undertaken at 2 and 5 years in a subset of patients. Results: In patients with choroideremia, mean retinal sensitivities at baseline were significantly greater in the smooth zone (26.1 ± 2.0 dB) versus the mottled zone (20.5 ± 4.2 dB) (P < 0.0001). Mean retinal sensitivities at baseline were similar in the smooth zone between choroideremia patients and controls (P = 0.054) but significantly impaired in the mottled zone in choroideremia compared to controls (P < 0.0001). The rate of decline in total sensitivity over 5 years was not significant in either the smooth or mottled zone in a small subset of choroideremia patients (n = 7; P = 0.344). Conclusions: In choroideremia, retinal sensitivity as determined by microperimetry correlates with patterns on AF imaging: retinal function in the smooth zone, where the retinal pigment epithelium is anatomically preserved, is similar to controls, but retinal sensitivity in the mottled zone is impaired. Translational Relevance: Patterns on AF imaging may represent a novel, objective outcome measure for clinical trials in choroideremia as a surrogate for retinal function.

Current and Future Landscape in Genetic Therapies for Leber Hereditary Optic Neuropathy.

Leber hereditary optic neuropathy (LHON) is the most common primary mitochondrial genetic disease that causes blindness in young adults. Over 50 inherited mitochondrial DNA (mtDNA) variations are associated with LHON; however, more than 95% of cases are caused by one of three missense variations (m.11778 G > A, m.3460 G > A, and m.14484 T > C) encoding for subunits ND4, ND1, and ND6 of the respiration complex I, respectively. These variants remain silent until further and currently poorly understood genetic and environmental factors precipitate the visual loss. The clinical course that ensues is variable, and a convincing treatment for LHON has yet to emerge. In 2015, an antioxidant idebenone (Raxone) received European marketing authorisation to treat visual impairment in patients with LHON, and since then it was introduced into clinical practice in several European countries. Alternative therapeutic strategies, including gene therapy and gene editing, antioxidant and neurotrophic agents, mitochondrial biogenesis, mitochondrial replacement, and stem cell therapies are being investigated in how effective they might be in altering the course of the disease. Allotopic gene therapies are in the most advanced stage of development (phase III clinical trials) whilst most other agents are in phase I or II trials or at pre-clinical stages. This manuscript discusses the phenotype and genotype of the LHON disease with complexities and peculiarities such as incomplete penetrance and gender bias, which have challenged the therapies in development emphasising the most recent use of gene therapy. Furthermore, we review the latest results of the three clinical trials based on adeno-associated viral (AAV) vector-mediated delivery of NADH dehydrogenase subunit 4 (ND4) with mitochondrial targeting sequence, highlighting the differences in the vector design and the rationale behind their use in the allotopic transfer.

The Role of Inflammation in Age-Related Macular Degeneration-Therapeutic Landscapes in Geographic Atrophy.

Age-related macular degeneration (AMD) is the leading cause of vision loss and visual impairment in people over 50 years of age. In the current therapeutic landscape, intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapies have been central to the management of neovascular AMD (also known as wet AMD), whereas treatments for geographic atrophy have lagged behind. Several therapeutic approaches are being developed for geographic atrophy with the goal of either slowing down disease progression or reversing sight loss. Such strategies target the inflammatory pathways, complement cascade, visual cycle or neuroprotective mechanisms to slow down the degeneration. In addition, retinal implants have been tried for vision restoration and stem cell therapies for potentially a dual purpose of slowing down the degeneration and restoring visual function. In particular, therapies focusing on the complement pathway have shown promising results with the FDA approved pegcetacoplan, a complement C3 inhibitor, and avacincaptad pegol, a complement C5 inhibitor. In this review, we discuss the mechanisms of inflammation in AMD and outline the therapeutic landscapes of atrophy AMD. Improved understanding of the various pathway components and their interplay in this complex neuroinflammatory degeneration will guide the development of current and future therapeutic options, such as optogenetic therapy.

Programmable RNA editing with endogenous ADAR enzymes - a feasible option for the treatment of inherited retinal disease?

RNA editing holds great promise for the therapeutic correction of pathogenic, single nucleotide variants (SNV) in the human transcriptome since it does not risk creating permanent off-targets edits in the genome and has the potential for innovative delivery options. Adenine deaminases acting on RNA (ADAR) enzymes catalyse the most widespread form of posttranscriptional RNA editing in humans and their ability to hydrolytically deaminate adenosine to inosine in double stranded RNA (dsRNA) has been harnessed to change pathogenic single nucleotide variants (SNVs) in the human genome on a transcriptional level. Until now, the most promising target editing rates have been achieved by exogenous delivery of the catalytically active ADAR deaminase domain (ADARDD) fused to an RNA binding protein. While it has been shown that endogenous ADARs can be recruited to a defined target site with the sole help of an ADAR-recruiting guide RNA, thus freeing up packaging space, decreasing the chance of an immune response against a foreign protein, and decreasing transcriptome-wide off-target effects, this approach has been limited by a low editing efficiency. Through the recent development of novel circular ADAR-recruiting guide RNAs as well as the optimisation of ADAR-recruiting antisense oligonucleotides, RNA editing with endogenous ADAR is now showing promising target editing efficiency in vitro and in vivo. A target editing efficiency comparable to RNA editing with exogenous ADAR was shown both in wild-type and disease mouse models as well as in wild-type non-human primates (NHP) immediately following and up to 6 weeks after application. With these encouraging results, RNA editing with endogenous ADAR has the potential to present an attractive option for the treatment of inherited retinal diseases (IRDs), a field where gene replacement therapy has been established as safe and efficacious, but where an unmet need still exists for genes that exceed the packaging capacity of an adeno associated virus (AAV) or are expressed in more than one retinal isoform. This review aims to give an overview of the recent developments in the field of RNA editing with endogenous ADAR and assess its applicability for the field of treatment of IRD.

Choroideremia: Toward Regulatory Approval of Retinal Gene Therapy.

Choroideremia is an X-linked inherited retinal degeneration characterized by primary centripetal degeneration of the retinal pigment epithelium (RPE), with secondary degeneration of the choroid and retina. Affected individuals experience reduced night vision in early adulthood with blindness in late middle age. The underlying CHM gene encodes REP1, a protein involved in the prenylation of Rab GTPases essential for intracellular vesicle trafficking. Adeno-associated viral gene therapy has demonstrated some benefit in clinical trials for choroideremia. However, challenges remain in gaining regulatory approval. Choroideremia is slowly progressive, which presents difficulties in demonstrating benefit over short pivotal clinical trials that usually run for 1-2 years. Improvements in visual acuity are particularly challenging due to the initial negative effects of surgical detachment of the fovea. Despite these challenges, great progress toward a treatment has been made since choroideremia was first described in 1872.

Microperimetry as an Outcome Measure in RPGR-associated Retinitis Pigmentosa Clinical Trials.

Purpose: To explore which microperimetry sensitivity index (pointwise sensitivity, mean sensitivity, and volume sensitivity) is suitable as a microperimetry outcome measure in patients with X-linked RPGR-associated retinitis pigmentosa (RP). Methods: Microperimetry data from patients with RPGR-associated RP were collected and analyzed retrospectively. Fourteen participants completed triplicate microperimetry testing, across 2 consecutive days for the repeatability analyses. Longitudinal data was obtained from 13 participants who completed microperimetry testing at two separate visits. Results: The test-retest coefficients of repeatability (CoR) for pointwise sensitivity were ±9.5 dB and ±9.3 dB, in the right and left eyes, respectively. The mean sensitivity CoR for the right and left eyes was ±0.7 dB and ±1.3 dB. Volume sensitivity CoR was ±144.5 dB*deg2 and ±324.2 dB*deg2 for the right and left eyes, respectively. The mean sensitivities were positively skewed toward zero in those with a high number of nonseeing points (arbitrarily assigned to -1.0 dB) and just seen points (0.0 dB). Volume sensitivities were unaffected by the averaging effects of skewed data. Conclusions: Clinical trials should report population-specific test-retest variability to determine a clinically significant change. Pointwise sensitivity indices should be used with caution as outcome measures in clinical trials owing to high levels of test-retest variability. Global indices seem to be less prone to variability. Volume sensitivity indices seem to be superior for use in RPGR-associated RP clinical trials compared with mean sensitivity because they are unaffected by the averaging effects of highly skewed data. Translational Relevance: Careful selection of sensitivity indices (VA) is required when using microperimetry as a clinical trial outcome measure.

Developmental Expression of the Cell Cycle Regulator p16INK4a in Retinal Glial Cells: A Novel Marker for Immature Ocular Astrocytes?

Retinal astrocytes are vital for neuronal homeostasis in the retina. Together with Müller glia, they provide retinal cells with neurotrophic factors, antioxidative support, and defense mechanisms such as the formation of the blood-retinal barrier. Substantial heterogeneity of astrocyte morphology and function represents a challenge for identification of distinct subtypes which may be potential targets for therapeutic purposes. Hence, identification of novel markers of astrocyte subpopulations is highly relevant to better understand the molecular mechanisms involved in retinal development, homeostasis, and pathology. In this study, we observed that the cell cycle regulator, p16INK4a, is expressed in immature astrocytes in the mouse retina. Immunohistochemical analysis showed p16INK4a expression in the optic nerve of wild-type mice from 3 days to 3 months of age and in the nerve fiber layer of the adult mouse retina. Colocalization of p16INK4a expression and glial fibrillary acidic protein (immature/mature astrocyte marker) tends to decrease with age. However, colocalization of p16INK4a expression and vimentin (immature astrocyte marker) remains high in the optic nerve from the early postnatal period to adulthood. The observations from this study provide a valuable tool for further investigations of ocular astrocytes in the developing retina as well as in degenerative retinopathies.