Repeatability of Quantitative Autofluorescence Imaging in a Multicenter Study Involving Patients With Recessive Stargardt Disease 1

Purpose

This study assesses the repeatability of quantitative autofluorescence (qAF) in a multicenter setting and evaluates qAF as the end point for clinical trials in recessive Stargardt disease 1 (STGD1).

Methods

A total of 102 patients with STGD1 underwent qAF imaging as part of the Stargardt Remofuscin Treatment Trial (STARTT; EudraCT No. 2018-001496-20). For 166 eyes, we obtained qAF imaging at 2 visits, with 2 recordings per visit. The qAF8 values were independently determined by the study site and a central reading center. Intra- and inter-visit reproducibility, as well as interobserver (study site versus reading center) reproducibility were obtained using intraclass correlation (ICC), one-sample t-test, and Bland-Altman coefficient of repeatability.

Results

The qAF repeatability was ± 26.1% for intra-visit, ± 40.5% for inter-visit, and ± 20.2% for the interobserver reproducibility measures. Intra-visit repeatability was good to excellent for all sites (ICC of 0.88-0.96). Variability between visits was higher with an overall ICC of 0.76 (0.69-0.81). We observed no significant difference in qAF values across sites between visits (7.06 ± 93.33, P = 0.238).

Conclusions

Real-life test-retest variability of qAF is higher in this set of data than previously reported in single center settings. With improved operator training and by selecting the better of two recordings for evaluation, qAF serves as a useful method for assessing changes in autofluorescence signal.

Translational Relevance

The qAF can be adopted as a clinical trial end point, but steps to counterbalance variability should be considered.

Biallelic Variants in TULP1 Are Associated with Heterogeneous Phenotypes of Retinal Dystrophy

Biallelic pathogenic variants in TULP1 are mostly associated with severe rod-driven inherited retinal degeneration. In this study, we analyzed clinical heterogeneity in 17 patients and characterized the underlying biallelic variants in TULP1. All patients underwent thorough ophthalmological examinations. Minigene assays and structural analyses were performed to assess the consequences of splice variants and missense variants. Three patients were diagnosed with Leber congenital amaurosis, nine with early onset retinitis pigmentosa, two with retinitis pigmentosa with an onset in adulthood, one with cone dystrophy, and two with cone-rod dystrophy. Seventeen different alleles were identified, namely eight missense variants, six nonsense variants, one in-frame deletion variant, and two splice site variants. For the latter two, minigene assays revealed aberrant transcripts containing frameshifts and premature termination codons. Structural analysis and molecular modeling suggested different degrees of structural destabilization for the missense variants. In conclusion, we report the largest cohort of patients with TULP1-associated IRD published to date. Most of the patients exhibited rod-driven disease, yet a fraction of the patients exhibited cone-driven disease. Our data support the hypothesis that TULP1 variants do not fold properly and thus trigger unfolded protein response, resulting in photoreceptor death.

Current Management of Inherited Retinal Degeneration Patients in Europe: Results of a 2-Year Follow-Up Multinational Survey by the European Vision Institute Clinical Research Network - EVICR.net

INTRODUCTION

An increasing number of gene-specific therapies are being developed for inherited retinal degenerations (IRDs). Identification of well-characterized patients is an emerging need. We conducted the second multinational survey among the EVICR.net and ERN-EYE members to understand the management and treatment of IRDs in Europe and compared it to the 2019 survey.

METHODS

An electronic survey questionnaire was developed and sent to 124 clinical centers (25 countries) by June/July 2021. Statistical analysis was performed with Excel and R.

RESULTS

The overall response rate was 44% but varied among countries. Only 9% of responding centers do not see IRD patients (2019 survey 14%), 42% follow at least 200 patients per year, 18% follow 500-999, and 2% more than 1,000. Databases exist in 86% of the centers (local 86%; national web based 12%). IRD patients are referred to EVICR.net and ERN-EYE centers mainly by general ophthalmologists, patient self-referral, or medical retina specialists. Most IRD patients are first seen as adults. Signs and symptoms depend on age of onset: in infancy, nystagmus; at older age, night blindness and reduced visual field; reduced visual acuity is described at any age. Comprehensive ophthalmic examination always includes visual acuity and almost always visual field multimodal retinal imaging, electrophysiology, color vision testing, and refraction. Identification of genotypes is successful in 72% of centers in 40-80% of cases (2019 survey 69% of centers). The time for confirmation of the genetic diagnosis varies from 2-4 weeks to 24 months (2019 survey >4 weeks ≤10 years). Genetic testing is covered by public health service in 83%, private health insurance in 29%, research funds in 24%; 5% do not have access to genetic testing (2019 survey 15%). The most striking result is the high increase in the involvement of centers in natural history and gene therapy trials that more than doubled for the latter.

DISCUSSION

This second multinational survey on management of IRDs in Europe highlights persistent important differences in the number of IRD patients managed per center, comparable diagnostic work-up, and increasing genotyping in diagnostic laboratories. The important increase in involvement of centers in natural history and gene therapy trials reflects the rapidly evolving field of gene therapy development. The survey provides important follow-up data for researchers, clinicians, caregivers, patient advocate groups, pharmaceutical companies, and investors.

Frequency-dependent retinal responsiveness to sinusoidal electrical stimulation in achromatopsia

Recently, we proposed a method to assess cell-specific retinal functions based on the frequency-dependent responses to sinusoidal transcorneal electrostimulation. In this study, we evaluated the alterations in responsiveness in achromatopsia patients to explore the frequency-selectivity of photoreceptors. The electrical stimulation was applied to one eye of genetically confirmed achromatopsia patients via corneal electrodes. The stimulus was composed of amplitude-modulated sine waves with variable carrier frequencies (4-30 Hz) and a steady low-frequency envelope. The retinal responsiveness across the spectrum was calculated based on the velocity and the synchronicity of the electrically evoked pupillary oscillations. Achromats displayed a characteristic peak in responsiveness in the 6-10 Hz range. In contrast, stimulus frequencies above 16 Hz elicited only weak pupil responses and weak phosphenes. Compared to the tuning curve of the healthy retina, responses to low-frequency stimulation appear to reflect mainly rod activation while higher frequencies seem to activate cones. The possibility to examine cell-specific retinal functions independently from their responses to light may improve our understanding of the structural changes in the retina induced by gene therapy.

Therapy with voretigene neparvovec. How to measure success?

Retinal gene supplementation therapy such as the first approved one, voretigene neparvovec, delivers a functioning copy of the missing gene enabling the protein transcription in retinal cells and restore visual functions. After gene supplementation for the genetic defect, a complex network of functional regeneration is the consequence, whereas the extent is very individualized. Diagnostic and functional testings that have been used routinely by ophthalmologists so far to define the correct diagnosis, cannot be applied in the new context of defining small, sometimes subtle changes in visual functions. New view on retinal diagnostics is needed to understand this processes that define safety and efficacy of the treatment. Not only does vision have many aspects that must be addressed by specific evaluations and imaging techniques, but objective readouts of local retinal function for rods and cones separately have been an unmet need until recently. A reliable test-retest variability is necessary in rare diseases such as inherited retinal dystrophies, because statistics are often not applicable due to a low number of participants. Methods for a reliable individual evaluation of the therapy success are needed. In this manuscript we present an elaboration on retinal diagnostics combining psychophysics (eg. full-field stimulus threshold or dark adapted perimetry) as well as objective measures for local retinal function (eg. photopic and scotopic chromatic pupil campimetry) and retinal imaging for a meaningful workflow to apply in evaluation of the individual success in patients receiving gene therapy for photoreceptor diseases.

Biallelic variants in coenzyme Q10 biosynthesis pathway genes cause a retinitis pigmentosa phenotype

The aim of this study was to investigate coenzyme Q10 (CoQ₁₀) biosynthesis pathway defects in inherited retinal dystrophy. Individuals affected by inherited retinal dystrophy (IRD) underwent exome or genome sequencing for molecular diagnosis of their condition. Following negative IRD gene panel analysis, patients carrying biallelic variants in CoQ₁₀ biosynthesis pathway genes were identified. Clinical data were collected from the medical records. Haplotypes harbouring the same missense variant were characterised from family genome sequencing (GS) data and direct Sanger sequencing. Candidate splice variants were characterised using Oxford Nanopore Technologies single molecule sequencing. The CoQ₁₀ status of the human plasma was determined in some of the study patients. 13 individuals from 12 unrelated families harboured candidate pathogenic genotypes in the genes: PDSS1, COQ2, COQ4 and COQ5. The PDSS1 variant c.589 A > G was identified in three affected individuals from three unrelated families on a possible ancestral haplotype. Three variants (PDSS1 c.468-25 A > G, PDSS1 c.722-2 A > G, COQ5 c.682-7 T > G) were shown to lead to cryptic splicing. 6 affected individuals were diagnosed with non-syndromic retinitis pigmentosa and 7 had additional clinical findings. This study provides evidence of CoQ₁₀ biosynthesis pathway gene defects leading to non-syndromic retinitis pigmentosa in some cases. Intronic variants outside of the canonical splice-sites represent an important cause of disease. RT-PCR nanopore sequencing is effective in characterising these splice defects.

The STArgardt Remofuscin Treatment Trial (STARTT): design and baseline characteristics of enrolled Stargardt patients

Background: This report describes the study design and baseline characteristics of patients with Stargardt disease (STGD1) enrolled in the STArgardt Remofuscin Treatment Trial (STARTT). Methods: In total, 87 patients with genetically confirmed STGD1 were randomized in a double-masked, placebo-controlled proof of concept trial to evaluate the safety and efficacy of 20 milligram oral remofuscin for 24 months. The primary outcome measure is change in mean quantitative autofluorescence value of an 8-segment ring centred on the fovea (qAF 8). Secondary efficacy variables are best corrected visual acuity (BCVA), low-luminance visual acuity (LLVA), mesopic microperimetry (mMP),  spectral domain optical coherence tomography (SD-OCT), reading speed on Radner reading charts, and patient-reported visual function as assessed by the National Eye Institute Visual Functioning Questionnaire 25 (NEI VFQ-25) and Functional Reading Independence (FRI) Index. Results: Mean age of participants was 35±11 years with 49 (56%) female. Median qAF 8 value was 438 Units (range 210-729). Median BCVA and LLVA in decimal units were 0.50 (range 0.13-0.80) and 0.20 (range 0.06-0.63), respectively. The median of the mean retinal sensitivity with mMP was 20.4 dB (range 0.0-28.8). SD-OCT showed median central subfield retinal thickness of 142 µm (range 72-265) and median macular volume of 1.65 mm 3 (range 1.13-2.19). Compared to persons without vision impairment, both reading performance and patient-reported visual function were significantly lower (p<0.001, one sample t-test). Mean reading speed was 108±39 words/minute with logRAD-score of 0.45±0.28. Mean VFQ-25 composite score was 72±13. Mean FRI Index score 2.8±0.6. Conclusions: This trial design may serve as reference for future clinical trials as it explores the utility of qAF 8 as primary outcome measure. The baseline data represent the largest, multi-national, STGD1 cohort to date that underwent standardized qAF imaging, reading speed assessment and vision-related quality of life measures which all contribute to the characterization of STGD1. EudraCT registration: 2018-001496-20 (09/05/2019).

Expression and subcellular localization of USH1C/harmonin in human retina provides insights into pathomechanisms and therapy

Usher syndrome (USH) is the most common form of hereditary deaf-blindness in humans. USH is a complex genetic disorder, assigned to three clinical subtypes differing in onset, course and severity, with USH1 being the most severe. Rodent USH1 models do not reflect the ocular phenotype observed in human patients to date; hence, little is known about the pathophysiology of USH1 in the human eye. One of the USH1 genes, USH1C, exhibits extensive alternative splicing and encodes numerous harmonin protein isoforms that function as scaffolds for organizing the USH interactome. RNA-seq analysis of human retinae uncovered harmonin_a1 as the most abundant transcript of USH1C. Bulk RNA-seq analysis and immunoblotting showed abundant expression of harmonin in Müller glia cells (MGCs) and retinal neurons. Furthermore, harmonin was localized in the terminal endfeet and apical microvilli of MGCs, presynaptic region (pedicle) of cones and outer segments (OS) of rods as well as at adhesive junctions between MGCs and photoreceptor cells (PRCs) in the outer limiting membrane (OLM). Our data provide evidence for the interaction of harmonin with OLM molecules in PRCs and MGCs and rhodopsin in PRCs. Subcellular expression and colocalization of harmonin correlate with the clinical phenotype observed in USH1C patients. We also demonstrate that primary cilia defects in USH1C patient-derived fibroblasts could be reverted by the delivery of harmonin_a1 transcript isoform. Our studies thus provide novel insights into PRC cell biology, USH1C pathophysiology and development of gene therapy treatment(s).

Cell-specific electrical stimulation of human retinal neurons assessed by pupillary response dynamics in vivo

Studies on the electrical excitability of retinal neurons show that photoreceptors and other cell types can be selectively activated by distinct stimulation frequencies in vitro. Yet, this principle still needs to be validated in humans in vivo. As a first step, this study explored the frequency preferences of human rods by means of transcorneal electrostimulation (TES), using the electrically-elicited pupillary responses (EEPRs) as an objective readout. The stimulation paradigm contained a 1.2 Hz sinusoidal envelope, which was superimposed on variable carrier frequencies (4-30 Hz). These currents were delivered to one of the participant's eyes via a corneal electrode and consensual pupillary reactions were recorded from the contralateral eye. The responsiveness of the retina at each frequency was assessed based on the EEPR dynamics. Differences between healthy participants and patients with retinitis pigmentosa were evaluated to identify the preferred frequency range of rods. The responsiveness of healthy individuals revealed a clear peak around 6-8 Hz. In contrast, the pupillary responses of patients were significantly reduced in the lower frequency range. These findings suggest that the responses in this frequency bin were selectively mediated by rods. This work provides evidence that different retinal cell types can be selectively activated via TES in vivo, and that this effect can be captured noninvasively using EEPRs. This knowledge may be exploited for the diagnostics and therapy of retinal diseases, e.g., to design cell-specific functional tests for the degenerating retina, or to optimize stimulation paradigms which are currently used by retinal prostheses.

Ophthalmic and Genetic Features of Bardet Biedl Syndrome in a German Cohort

The aim of this study was to characterize the ophthalmic and genetic features of Bardet Biedl (BBS) syndrome in a cohort of patients from a German specialized ophthalmic care center. Sixty-one patients, aged 5−56 years, underwent a detailed ophthalmic examination including visual acuity and color vision testing, electroretinography (ERG), visually evoked potential recording (VEP), fundus examination, and spectral domain optical coherence tomography (SD-OCT). Adaptive optics flood illumination ophthalmoscopy was performed in five patients. All patients had received diagnostic genetic testing and were selected upon the presence of apparent biallelic variants in known BBS-associated genes. All patients had retinal dystrophy with morphologic changes of the retina. Visual acuity decreased from ~0.2 (decimal) at age 5 to blindness 0 at 50 years. Visual field examination could be performed in only half of the patients and showed a concentric constriction with remaining islands of function in the periphery. ERG recordings were mostly extinguished whereas VEP recordings were reduced in about half of the patients. The cohort of patients showed 51 different likely biallelic mutations—of which 11 are novel—in 12 different BBS-associated genes. The most common associated genes were BBS10 (32.8%) and BBS1 (24.6%), and by far the most commonly observed variants were BBS10 c.271dup;p.C91Lfs*5 (21 alleles) and BBS1 c.1169T>G;p.M390R (18 alleles). The phenotype associated with the different BBS-associated genes and genotypes in our cohort is heterogeneous, with diverse features without genotype−phenotype correlation. The results confirm and expand our knowledge of this rare disease.

Comprehensive variant spectrum of the CNGA3 gene in patients affected by achromatopsia

Achromatopsia (ACHM) is a congenital cone photoreceptor disorder characterized by impaired color discrimination, low visual acuity, photosensitivity, and nystagmus. To date, six genes have been associated with ACHM (CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, and ATF6), the majority of these being implicated in the cone phototransduction cascade. CNGA3 encodes the CNGA3 subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors and is one of the major disease-associated genes for ACHM. Herein, we provide a comprehensive overview of the CNGA3 variant spectrum in a cohort of 1060 genetically confirmed ACHM patients, 385 (36.3%) of these carrying "likely disease-causing" variants in CNGA3. Compiling our own genetic data with those reported in the literature and in public databases, we further extend the CNGA3 variant spectrum to a total of 316 variants, 244 of which we interpreted as "likely disease-causing" according to ACMG/AMP criteria. We report 48 novel "likely disease-causing" variants, 24 of which are missense substitutions underlining the predominant role of this mutation class in the CNGA3 variant spectrum. In addition, we provide extensive in silico analyses and summarize reported functional data of previously analyzed missense, nonsense and splicing variants to further advance the pathogenicity assessment of the identified variants.

Novel OPN1LW/OPN1MW Exon 3 Haplotype-Associated Splicing Defect in Patients with X-Linked Cone Dysfunction

Certain combinations of common variants in exon 3 of OPN1LW and OPN1MW, the genes encoding the apo-protein of the long- and middle-wavelength sensitive cone photoreceptor visual pigments in humans, induce splicing defects and have been associated with dyschromatopsia and cone dysfunction syndromes. Here we report the identification of a novel exon 3 haplotype, G-C-G-A-T-T-G-G (referring to nucleotide variants at cDNA positions c.453, c.457, c.465, c.511, c.513, c.521, c.532, and c.538) deduced to encode a pigment with the amino acid residues L-I-V-V-A at positions p.153, p.171, p.174, p.178, and p.180, in OPN1LW or OPN1MW or both in a series of seven patients from four families with cone dysfunction. Applying minigene assays for all observed exon 3 haplotypes in the patients, we demonstrated that the novel exon 3 haplotype L-I-V-V-A induces a strong but incomplete splicing defect with 3-5% of residual correctly spliced transcripts. Minigene splicing outcomes were similar in HEK293 cells and the human retinoblastoma cell line WERI-Rb1, the latter retaining a cone photoreceptor expression profile including endogenous OPN1LW and OPN1MW gene expression. Patients carrying the novel L-I-V-V-A haplotype presented with a mild form of Blue Cone Monochromacy or Bornholm Eye Disease-like phenotype with reduced visual acuity, reduced cone electroretinography responses, red-green color vision defects, and frequently with severe myopia.

Central Visual Function and Genotype-Phenotype Correlations in PDE6A-Associated Retinitis Pigmentosa

Purpose

Autosomal recessive retinitis pigmentosa (arRP) can be caused by mutations in the phosphodiesterase 6A (PDE6A) gene. Here, we describe the natural course of disease progression with respect to central retinal function (i.e., visual acuity, contrast sensitivity, and color vision) and establish a detailed genotype-–phenotype correlation.

Methods

Forty-four patients (26 females; mean age ± SD, 43 ± 13 years) with a confirmed genetic diagnosis of PDE6A-associated arRP underwent comprehensive ophthalmological examinations including best-corrected visual acuity (BCVA) with Early Treatment Diabetic Retinopathy Study charts, contrast sensitivity (CS) with Pelli–Robson charts at distances of 3 m and 1 m, and color vision testing using Roth 28-Hue and Panel D-15 saturated color cups.

Results

The most frequently observed variants were c.998+1G>A/p.?, c.304C>A/p.R102S, and c.2053G>A/p.V685M. Central retinal function in patients homozygous for variant c.304C>A/p.R102S was better when compared to patients homozygous for variant c.998+1G>A/p.?, although the former were older at baseline. Central retinal function was similar in patients homozygous for variant c.304C>A/p.R102S and patients heterozygous for variants c.304C>A/p.R102S and c.2053G>A/p.V685M, although the latter were younger at baseline. Annual decline rates in central retinal function were small.

Conclusions

We conclude that the severity of the different disease-causing PDE6A mutations in humans with respect to central visual function may be ranked as follows: c.2053G>A/p.V685M in homozygous state (most severe) > c.998+1G>A/p.? in homozygous state > c.304C>A/p.R102S and c.2053G>A/p.V685M in compound-heterozygous state > c.304C>A/p.R102S in homozygous state (mildest). The assessment of treatment efficacy in interventional trials will remain challenging due to small annual decline rates in central retinal function.

Short term morphological rescue of the fovea after gene therapy with voretigene neparvovec

PURPOSE

Leber congenital amaurosis type 2 (LCA2) and early-onset severe retinal dystrophy (EOSRD) are linked to visual impairment with nyctalopia and visual acuity reduction in early childhood. In 2017, the first gene therapy voretigene neparvovec (Luxturna™) for patients with LCA and EOSRD cause by bi-allelic mutations in the RPE65 gene has been approved. Here we report on an example of short-term change in the foveal morphology after functionally successful gene therapy with voretigene neparvovec in a 15-year old patient.

METHODS

The clinical examinations included best corrected visual acuity (BCVA), spectral domain optical coherence tomography (OCT) and adaptive optics retinal imaging.

RESULTS

During follow-up over a period of 3 months after the treatment, an improvement of the central foveal morphology could be observed in OCT, with a clear demarcation of the external limiting membrane and changes in the photoreceptor mosaic on adaptive optics retinal imaging. These morphological rescue parameters correlated in part with the improvement in foveal-mediated vision after the treatment and adaptive optics imaging. Although the visual acuity improved only slightly at month 3, objective central cone evaluation with chromatic pupil campimetry showed an increase in the central sensitivity. In daily life, the patient reported her visional experience after the treatment as 'brighter'.

CONCLUSION

Rapid changes in the correlates of photoreceptor morphology after successful gene therapy in patients with LCA/EORD can be quantifiable on individual level.

Disease expression caused by different variants in the BEST1 gene: genotype and phenotype findings in bestrophinopathies

Purpose:

To analyse the spectrum of clinical features and molecular genetic data in a series of patients carrying likely disease-associated variants in the BEST1 gene.

Methods:

Retrospective observational analysis of clinical data extracted from the medical records of visual function, multimodal imaging and electrophysiology of 62 eyes of 31 patients. Molecular genetic analysis was performed by means of panel-based NGS or Sanger sequencing.

Results:

The spectrum of variants in the BEST1 gene comprised 19 different variants and three of which are novel. Fundus photographs and OCT images allowed categorization of 52 eyes as Best vitelliform macular dystrophy (BVMD) with stages 1 to 5 and 10 eyes with autosomal recessive bestrophinopathy (ARB), with more severe phenotype. One patient was shown to be heterozygous for a variant, which has so far been described only in ARB, but this patient had the BVMD phenotype. There was no significant progression of the visual acuity during the follow-up period of 5 years both in BVMD and ARB. The most prevalent pattern of fundus autofluorescence (FAF) in BVMD was ‘patchy’. There were diverse visual field defects in static automated perimetry (SAP) depending on the stage. The Arden ratio was significantly lower in ARB patients and in eyes with stage 5 of BVMD.

Conclusions:

The genotype does not always predict the phenotype in patients with BVMD and ARB; however, having two mutations in the BEST1 gene causes a more severephenotype. FAFhelped to distinguish ARB from BVMD. Most of the observed eyesdidnotprogressfunctionallyduringthefollow-up.ARBandtheatrophicstageof BVMD as the disease end-stage had the worst visual functions and EOG results.

Quantification of the Dynamic Visual Acuity Space at Real-World Luminances and Contrasts: The VA-CAL Test

Purpose

Best-corrected visual acuity (BCVA) is assessed at a single standardized luminance with maximum optotype contrast, not reflecting the constantly changing daily-life viewing conditions. For a more realistic estimation of visual performance at varying object contrasts (Cs) and ambient luminances (ALs), we developed a new VA test, VA-CAL.

Methods

Landolt-C-rings between 18% and 95% Weber contrast, were presented at 1 m distance (8 Alternative Forced Choice) on a 5.7 degree field in the middle of a frosted glass screen (66 degrees), back-lit by 3060 LEDs (generating ambient luminances between 0-10,000 cd/m²). Visual acuity (VA) was measured in 14 normally sighted participants twice for 8 conditions of ambient luminance and 6 conditions of contrast using a QUEST staircase procedure.

Results

VA improved continuously up to an ambient luminance of 3000 to 5000 cd/m² (best mean VA ± SEM: -0.47 ± 0.03 logMAR at C = 95%, AL = 3000 cd/m²), followed by a decline of VA at higher luminances with good test-retest variability. As expected, reduced contrast leads to a lower VA (worst mean VA ± SEM: -0.03 ± 0.03 logMAR at C = 18%, AL = 0 cd/m²). A 3D plot of these data shows the VA space (VAS) extending between the contrast and luminance axes, which describes the dynamics of VA continuously changing under varying everyday life conditions.

Conclusions

VA-CAL, an automated device and procedure, allows for simultaneous evaluation of VA at various contrast-luminance combinations, thus providing a more comprehensive assessment of spatial vision problems not seen with standard BCVA tests.

Translational Relevance

The new BCVA test VA-CAL incorporates a range of everyday contrast and ambient luminance conditions for a more realistic description of visual performance.

Molecular Properties of Human Guanylate Cyclase-Activating Protein 3 (GCAP3) and Its Possible Association with Retinitis Pigmentosa

The cone-specific guanylate cyclase-activating protein 3 (GCAP3), encoded by the GUCA1C gene, has been shown to regulate the enzymatic activity of membrane-bound guanylate cyclases (GCs) in bovine and teleost fish photoreceptors, to an extent comparable to that of the paralog protein GCAP1. To date, the molecular mechanisms underlying GCAP3 function remain largely unexplored. In this work, we report a thorough characterization of the biochemical and biophysical properties of human GCAP3, moreover, we identified an isolated case of retinitis pigmentosa, in which a patient carried the c.301G>C mutation in GUCA1C, resulting in the substitution of a highly conserved aspartate residue by a histidine (p.(D101H)). We found that myristoylated GCAP3 can activate GC1 with a similar Ca2+-dependent profile, but significantly less efficiently than GCAP1. The non-myristoylated form did not induce appreciable regulation of GC1, nor did the p.D101H variant. GCAP3 forms dimers under physiological conditions, but at odds with its paralogs, it tends to form temperature-dependent aggregates driven by hydrophobic interactions. The peculiar properties of GCAP3 were confirmed by 2 ms molecular dynamics simulations, which for the p.D101H variant highlighted a very high structural flexibility and a clear tendency to lose the binding of a Ca2+ ion to EF3. Overall, our data show that GCAP3 has unusual biochemical properties, which make the protein significantly different from GCAP1 and GCAP2. Moreover, the newly identified point mutation resulting in a substantially unfunctional protein could trigger retinitis pigmentosa through a currently unknown mechanism.

The RUSH2A Study: Dark-Adapted Visual Fields in Patients With Retinal Degeneration Associated With Biallelic Variants in the USH2A Gene

Purpose

To measure visual fields using two-color dark-adapted chromatic perimetry in a subset of participants in the Rate of Progression of USH2A-related Retinal Degeneration (RUSH2A), a study of USH2A-mediated syndromic (USH2) and autosomal recessive nonsyndromic retinitis pigmentosa, determine percentage retaining rod function, and explore relationships between dark-adapted visual fields (DAVF) and rod function from ERG and full-field stimulus thresholds (FST).

Methods

Full-field rod mean sensitivity, number of rod loci, maximum sensitivity, DAVF full-field hill of vision (DAVF VTOT), and 30° hill of vision (DAVF V30) were measured in one eye for DAVF ancillary study participants (n = 49). Loci where cyan relative to red sensitivity was more than 5 dB on dark-adapted chromatic perimetry were considered rod mediated. Correlation coefficients between the DAVF measures and standard clinical measures were estimated, as were kappa statistics (κ) for agreement between DAVF and other measures of rod function.

Results

Of 49 participants tested with DAVF, 38 (78%) had evidence of rod function, whereas 15 (31%) had measurable rod ERGs. DAVF maximum sensitivity was highly correlated with FST white thresholds (r = -0.80; P < .001). Although not statistically significant, the number of rod loci and DAVF VTOT were lower in eyes with longer disease duration by 0.82 (95% confidence interval, -1.76, 0.12) loci/year and 0.59 (95% confidence interval, -1.82, 0.64) dB-steradians/year, respectively.

Conclusions

Rod-mediated function on FST and DAVF is present in many patients with symptomatic USH2A-related retinal degeneration, including some without measurable rod ERGs. RUSH2A longitudinal data will determine how these measures change with disease progression and whether they are useful for longitudinal studies in inherited retinal degenerations.

Evaluation of Local Rod and Cone Function in Stargardt Disease

Purpose

In this study, chromatic pupil campimetry (CPC) was used to map local functional degenerative changes of cones and rods in Stargardt disease (STGD1).

Methods

19 patients (age 36 ± 8 years; 12 males) with genetically confirmed ABCA4 mutations and a clinical diagnosis of STGD1 and 12 age-matched controls (age 37 ± 11 years; 2 males) underwent scotopic (rod-favoring) and photopic (cone-favoring) CPC. CPC evaluates the local retinal function in the central 30° visual field via analysis of the pupil constriction to local stimuli in a gaze-corrected manner.

Results

Scotopic CPC revealed that the rod function of patients with STGD1 inside the 30° visual field was not impaired when compared with age-matched controls. However, a statistically significant faster pupil response onset time (∼ 40 ms) was observed in the measured area. Photopic CPC showed a significant reduction of the central cone function up to 6°, with a minor, non-significant reduction beyond this eccentricity. The time dynamic of the pupillary response in photopic CPC did not reveal differences between STGD1 and controls.

Conclusions

The functional analysis of the macular region in STGD1 disease indicates reduced central cone function, corresponding to photoreceptor degeneration. In contrast, the rod function in the central area was not affected. Nevertheless, some alteration of the time dynamics in the rod system was observed indicating a complex effect of cone degeneration on the functional performance of the rod system. Our results should be considered when interpreting safety and efficacy in interventional trials of STGD1.

RNA-based therapies in inherited retinal diseases

Inherited retinal diseases (IRDs) are a genetically and phenotypically heterogeneous group of genetic eye disorders. There are more than 300 disease entities, and together this group of disorders affects millions of people globally and is a frequent cause of blindness or low-vision certification. However, each type is rare or ultra-rare. Characteristically, the impaired vision in IRDs is due to retinal photoreceptor dysfunction and loss resulting from mutation in a gene that codes for a retinal protein. Historically, IRDs have been considered incurable and individuals living with these blinding conditions could be offered only supportive care. However, the treatment landscape for IRDs is beginning to evolve. Progress is being made, driven by improvements in understanding of genotype-phenotype relationships, through advances in molecular genetic testing and retinal imaging. Alongside this expanding knowledge of IRDs, the current era of precision medicine is fueling a growth in targeted therapies. This has resulted in the first treatment for an IRD being approved. Several other therapies are currently in development in the IRD space, including RNA-based therapies, gene-based therapies (such as augmentation therapy and gene editing), cell therapy, visual prosthetics, and optogenetics. RNA-based therapies are a novel approach within precision medicine that have demonstrated success, particularly in rare diseases. Three antisense oligonucleotides (AONs) are currently in development for the treatment of specific IRD subtypes. These RNA-based therapies bring several key advantages in the setting of IRDs, and the potential to bring meaningful vision benefit to individuals living with inherited blinding disorders. This review will examine the increasing breadth and relevance of RNA-based therapies in clinical medicine, explore the key features that make AONs suitable for treating genetic eye diseases, and provide an overview of the three-leading investigational AONs in clinical trials.

Oscillatory Potentials in Achromatopsia as a Tool for Understanding Cone Retinal Functions

Achromatopsia (ACHM) is an inherited autosomal recessive disease lacking cone photoreceptors functions. In this study, we characterize the time-frequency representation of the full-field electroretinogram (ffERG) component oscillatory potentials (OPs), to investigate the connections between photoreceptors and the inner retinal network using ACHM as a model. Time-frequency characterization of OPs was extracted from 52 controls and 41 achromat individuals. The stimulation via ffERG was delivered under dark-adaptation (DA, 3.0 and 10.0 cd·s·m-2) to assess mixed rod-cone responses. The ffERG signal was subsequently analyzed using a continuous complex Morlet transform. Time-frequency maps of both DA conditions show the characterization of OPs, disclosing in both groups two distinct time-frequency windows (~70-100 Hz and >100 Hz) within 50 ms. Our main result indicates a significant cluster (p < 0.05) in both conditions of reduced relative power (dB) in ACHM people compared to controls, mainly at the time-frequency window >100 Hz. These results suggest that the strongly reduced but not absent activity of OPs above 100 Hz is mostly driven by cones and only in small part by rods. Thus, the lack of cone modulation of OPs gives important insights into interactions between photoreceptors and the inner retinal network and can be used as a biomarker for monitoring cone connection to the inner retina.

CT Assessment of Intraorbital Cable Movement of Electronic Subretinal Prosthesis in Three Different Surgical Approaches

Purpose

Electronic retinal implants restore some visual perception in patients blind from retinitis pigmentosa. Eye movements cause mechanical stress in intraorbital power supply cables leading to cable breaks. By using computer tomography (CT) scans at the extreme positions of the four cardinal gaze directions, this study determined in vivo, which of three surgical routing techniques results in minimal bending radius variation and favors durability.

Methods

Nine patients received the first-generation subretinal implant Alpha IMS (Retina Implant AG, Reutlingen, Germany) in one eye. Three techniques for intraorbital cable routing were used (straight cable route (A), parabulbar loop (B), and encircling band (C)), each in three patients. All patients underwent computer tomography of the orbital region. The bending radius of the intraorbital cable was measured with the DICOM viewer Osirix v4.1.2 (Pixmeo SARL, Bernex, Switzerland) and served as indicator for mechanical stress.

Results

Average bending radius variation was 87% for method A, 11% for method B, and 16% for method C. Methods A and B (P = 0.005) and methods A and C (P = 0.007) differed significantly, while method B and C showed no statistical difference (P = 0.07).

Conclusions

Compared to straight routes, arcuated cable routes significantly reduce cable movement and bending. Due to an easier surgical procedure, a parabulbar loop is the preferred method to minimize bending radius variation and prolong survival time of electronic subretinal implants.

Translational Relevance

CT analysis of cable bending of implanted medical devices allows to determine which surgical routing technique favors durability in vivo.

Auditory and olfactory findings in patients with USH2A-related retinal degeneration-Findings at baseline from the rate of progression in USH2A-related retinal degeneration natural history study (RUSH2A)

Sensorineural hearing loss (SNHL) is characteristic of Usher syndrome type 2 (USH2), but less is known about SNHL in nonsyndromic autosomal recessive retinitis pigmentosa (ARRP) and olfaction in USH2A-associated retinal degeneration. The Rate of Progression of USH2A-related Retinal Degeneration (RUSH2A) is a natural history study that enrolled 127 participants, 80 with USH2 and 47 with ARRP. Hearing was measured by pure-tone thresholds and word recognition scores, and olfaction by the University of Pennsylvania Smell Identification Test (UPSIT). SNHL was moderate in 72% of USH2 participants and severe or profound in 25%, while 9% of ARRP participants had moderate adult-onset SNHL. Pure-tone thresholds worsened with age in ARRP but not in USH2 participants. The degree of SNHL was not associated with other participant characteristics in either USH2 or ARRP. Median pure-tone thresholds in ARRP participants were significantly higher than the normative population (p < 0.001). Among 14 USH2 participants reporting newborn hearing screening results, 7 reported passing. Among RUSH2A participants, 7% had mild microsmia and 5% had moderate or severe microsmia. Their mean (±SD) UPSIT score was 35 (±3), similar to healthy controls (34 [±3]; p = 0.39). Olfaction differed by country (p = 0.02), but was not significantly associated with clinical diagnosis, age, gender, race/ethnicity, smoking status, visual measures, or hearing. Hearing loss in USH2A-related USH2 did not progress with age. ARRP patients had higher pure-tone thresholds than normal. Newborn hearing screening did not identify all USH2A-related hearing loss. Olfaction was not significantly worse than normal in participants with USH2A-related retinal degeneration.