Changes in Retinal Sensitivity Associated With Cotoretigene Toliparvovec in X-Linked Retinitis Pigmentosa With RPGR Gene Variations

Safety and efficacy of ATSN-101 in patients with Leber congenital amaurosis caused by biallelic mutations in GUCY2D: a phase 1/2, multicentre, open-label, unilateral dose escalation study

BACKGROUND

Leber congenital amaurosis 1 (LCA1), caused by mutations in GUCY2D, is a rare inherited retinal disease that typically causes blindness in early childhood. The aim of this study was to evaluate the safety and preliminary efficacy of ascending doses of ATSN-101, a subretinal AAV5 gene therapy for LCA1.

METHODS

15 patients with genetically confirmed biallelic mutations in GUCY2D were included in this phase 1/2 study. All patients received unilateral subretinal injections of ATSN-101. In the dose-escalation phase, three adult cohorts (n=3 each) were treated with three ascending doses: 1·0 × 1010 vg/eye (low dose), 3·0 × 1010 vg/eye (middle dose), and 1·0 × 1011 vg/eye (high dose). In the dose-expansion phase, one adult cohort (n=3) and one paediatric cohort (n=3) were treated at the high dose. The primary endpoint was the incidence of treatment-emergent adverse events (TEAEs), and secondary endpoints included full-field stimulus test (FST) and best-corrected visual acuity (BCVA). A multi-luminance mobility test (MLMT) was also done. Data through the 12-month main study period are reported.

FINDINGS

Patients were enrolled between Sept 12, 2019, and May 5, 2022. A total of 68 TEAEs were observed, 56 of which were related to the surgical procedure. No serious TEAE was related to the study drug. Ocular inflammation was mild and reversible with steroid treatment. For patients who received the high dose, mean change in dark-adapted FST was 20·3 decibels (dB; 95% CI 6·6 to 34·0) for treated eyes and 1·1 dB (-3·7 to 5·9) for untreated eyes at month 12 (white stimulus); improvements were first observed at day 28 and persisted over 12 months (p=0·012). Modest improvements in BCVA were also observed (p=0·10). Three of six patients who received the high dose and did the MLMT achieved the maximum score in the treated eye.

INTERPRETATION

ATSN-101 is well tolerated 12 months after treatment, with no drug-related serious adverse events. Clinically significant improvements in retinal sensitivity were sustained in patients receiving the high dose.

FUNDING

Atsena Therapeutics.

Gene Therapies in Clinical Development to Treat Retinal Disorders

Gene therapies have emerged as promising treatments in clinical development for various retinal disorders, offering hope to patients with inherited degenerative eye conditions. Several gene therapies have already shown remarkable success in clinical trials, with significant improvements observed in visual acuity and the preservation of retinal function. A multitude of gene therapies have now been delivered safely in human clinical trials for a wide range of inherited retinal disorders but there are some gaps in the reported trial data. Some of the most exciting treatment options are not under peer review and information is only available in press release form. Whilst many trials appear to have delivered good outcomes of safety, others have failed to meet primary endpoints and therefore not proceeded to phase III. Despite this, such trials have enabled researchers to learn how best to assess and monitor patient outcomes, which will guide future trials to greater success. In this review, we consider recent and ongoing clinical trials for a variety of potential retinal gene therapy treatments and discuss the positive and negative issues related to these trials. We discuss the treatment potential following clinical trials as well as the potential risks of some treatments under investigation. As these therapies continue to advance through rigorous testing and regulatory approval processes, they hold the potential to revolutionise the landscape of retinal disorder treatments, providing renewed vision and enhancing the quality of life for countless individuals worldwide.

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.

From onset to blindness: a comprehensive analysis of RPGR-associated X-linked retinopathy in a large cohort in China

BACKGROUND

Variants in the RPGR are the leading cause of X-linked retinopathies (XLRPs). Further in-depth investigation is needed to understand the natural history.

METHODS

Review of all case records, molecular genetic testing results, best-corrected visual acuity (BCVA), retinal imaging data (including fundus autofluorescence imaging and optical coherence tomography (OCT)), static visual field (VF) assessments and full-field electroretinogram.

RESULTS

Genetic testing was conducted on 104 male patients from 89 family pedigrees, identifying 22 novel variants and 1 de novo variant. The initial symptoms appeared in 78.2% of patients at a median age of 5 years. BCVA declined at a mean rate of 0.02 (IQR, 0-0.04) logarithm of the minimum angle of resolution per year, with a gradual, non-linear decrease over the first 40 years. Autofluorescence imaging revealed macular atrophy at a median age of 36.1 (IQR, 29.9-43.2) years. Patients experienced blindness at a median age of 42.5 (IQR, 32.9-45.2) years according to WHO visual impairment categories. OCT analysis showed a mean ellipsoid zone narrowing rate of 23.3 (IQR, -1.04-22.29) µm/month, with an accelerated reduction in the first 40 years (p<0.01). The median age at which ERG no longer detected a waveform was 26.5 (IQR, 20.5-32.8) years. Comparison by variant location indicated faster progression in patients with exon 1-14 variants during the initial two decades, while those with ORF15 variants showed accelerated progression from the third decade.

CONCLUSIONS

We provide a foundation for determining the treatment window and an objective basis for evaluating the therapeutic efficacy of gene therapy for XLRP.

Genetic therapies and potential therapeutic applications of CRISPR activators in the eye

Conventional gene therapy involving supplementation only treats loss-of-function diseases and is limited by viral packaging sizes, precluding therapy of large genes. The discovery of CRISPR/Cas has led to a paradigm shift in the field of genetic therapy, with the promise of precise gene editing, thus broadening the range of diseases that can be treated. The initial uses of CRISPR/Cas have focused mainly on gene editing or silencing of abnormal variants via utilising Cas endonuclease to trigger the target cell endogenous non-homologous end joining. Subsequently, the technology has evolved to modify the Cas enzyme and even its guide RNA, leading to more efficient editing tools in the form of base and prime editing. Further advancements of this CRISPR/Cas technology itself have expanded its functional repertoire from targeted editing to programmable transactivation, shifting the therapeutic focus to precise endogenous gene activation or upregulation with the potential for epigenetic modifications. In vivo experiments using this platform have demonstrated the potential of CRISPR-activators (CRISPRa) to treat various loss-of-function diseases, as well as in regenerative medicine, highlighting their versatility to overcome limitations associated with conventional strategies. This review summarises the molecular mechanisms of CRISPRa platforms, the current applications of this technology in vivo, and discusses potential solutions to translational hurdles for this therapy, with a focus on ophthalmic diseases.

Correlations between the Michigan Retinal Degeneration Questionnaire and visual function parameters in patients with retinitis pigmentosa

PURPOSE

To validate the use of best-corrected visual acuity (BCVA), low-luminance visual acuity (LLVA), low-luminance deficit (LLD; the difference between BCVA and LLVA), mean macular sensitivity and fixation stability as parameters of vision-related quality of life based on the novel Michigan Retinal Degeneration Questionnaire (MRDQ) in retinitis pigmentosa (RP) patients.

METHODS

In this prospective cross sectional study, 30 patients with RP (47% female) were included with a median age of 41.0 years (interquartile range: 24.1-58.3 years). BCVA, LLVA and LLD were measured with Early Treatment Diabetic Retinopathy Study (ETDRS) charts. Mesopic microperimetry was performed to measure mean macular sensitivity and fixation stability. Patients completed a Dutch translation of the MRDQ which results in an experienced disability (Θ-)score of seven domains. Spearman's rank correlation was used.

RESULTS

BCVA correlated significantly to the MRDQ domain of central vision (r = 0.657; p < 0.001) and colour vision (r = 0.524; p = 0.003). Lower LLVA significantly correlated to higher experienced disability in the MRDQ domains for central vision (=0.550; p = 0.002) and contrast sensitivity (r = 0.502; p = 0.005). LLD was significantly correlated to the MRDQ domains of scotopic function (r = -0.484; p = 0.007) and mesopic peripheral function (r = -0.533; p = 0.002). Lower mean macular sensitivity was significantly associated with high experienced disability in all domains except for photosensitivity.

CONCLUSIONS

The majority of the MRDQ domains is strongly associated with visual function parameters. These findings show that visual function measurements, especially LLVA, LLD and mean macular sensitivity on microperimetry, reflect vision-related quality of life and can be used as relevant outcome measures in clinical trials for RP.

Robotising vitreoretinal surgeries

The use of robotic surgery in ophthalmology has been shown to offer many potential advantages to current surgical techniques. Vitreoretinal surgery requires complex manoeuvres and high precision, and this is an area that exceeds manual human dexterity in certain surgical situations. With the advent of advanced therapeutics such as subretinal gene therapy, precise delivery and minimising trauma is imperative to optimize outcomes. There are multiple robotic systems in place for ophthalmology in pre-clinical and clinical use, and the Preceyes Robotic Surgical System (Preceyes BV) has also gained the CE mark and is commercially available for use. Recent in-vivo and in-human surgeries have been performed successfully with robotics systems. This includes membrane peeling, subretinal injections of therapeutics, and retinal vein cannulation. There is huge potential to integrate robotic surgery into mainstream clinical practice. In this review, we summarize the existing systems, and clinical implementation so far, and highlight the future clinical applications for robotic surgery in vitreo-retina.

Exploring self-reported visual function and vision-related anxiety in patients with RPGR-associated retinal degeneration

Variants in the retinitis pigmentosa GTPase regulator (RPGR) gene are responsible for the majority of X-linked retinitis pigmentosa cases, which not only affects male patients but also some heterozygous females. Vision-related disability and anxiety of patients with RPGR-associated retinal degeneration have never been explored before. This study aimed to evaluate self-reported visual function and vision-related anxiety in a Portuguese cohort of male and female patients with RPGR-associated retinal degeneration using two validated patient-reported outcome measures. Cross-sectional data of thirty-two genetically-tested patients was examined, including scores of the Michigan retinal degeneration questionnaire (MRDQ) and Michigan vision-related anxiety questionnaire. Patients were classified according to retinal phenotypes in males (M), females with male phenotype (FM), and females with radial or focal pattern. Both M and FM revealed higher rod-function and cone-function anxiety scores (p < 0.017). Most MRDQ disability scores were higher in M and FM (p < 0.004). Overall, positive correlations (p < 0.004) were found between every MRDQ domain and both anxiety scores. In RPGR-associated retinal degeneration, males and females with male phenotype show similar levels of increased vision-related anxiety and disability. Every MRDQ visual function domain showed a strong correlation with anxiety scores.

Current Status of Clinical Trials Design and Outcomes in Retinal Gene Therapy

With the rapid expansion of methods encompassed by the term gene therapy, new trials exploring the safety and efficacy of these methods are initiated more frequently. As a result, important questions arise pertaining the design of these trials and patient participation. One of the most important aspects of any clinical trial is the ability to measure the trial's outcome in a manner that will reflect the effect of the treatment and allow its quantification, whether the trial is aimed at preservation or restoration of retinal cells (photoreceptors and others), vision, or both. Here we will review the existing methods for quantification of trial outcomes, stressing the importance of assessing the participant's visual function and not just visual acuity. We will also describe the key considerations in trial design. Finally, as patient safety remains the primary concern in any trial participation, we will outline the key principles in that regard.

Phase 1/2 AAV5-hRKp.RPGR (Botaretigene Sparoparvovec) Gene Therapy: Safety and Efficacy in RPGR-Associated X-Linked Retinitis Pigmentosa

PURPOSE

To assess the safety and efficacy of AAV5-hRKp.RPGR in participants with retinitis pigmentosa GTPase regulator (RPGR)-associated X-linked retinitis pigmentosa (XLRP).

DESIGN

Open-label, phase 1/2 dose escalation/expansion study (ClinicalTrials.gov Identifier: NCT03252847).

METHODS

Males (≥5 years old) with XLRP-RPGR were evaluated. In the dose escalation phase, subretinal AAV5-hRKp.RPGR (low: 1.0 × 1011 vg/ml; intermediate: 2.0 × 1011 vg/ml; high: 4.0 × 1011 vg/ml) was administered to the poorer-seeing eye (n = 10). Dose confirmation (intermediate dose) was carried out in 3 pediatric participants. In the dose expansion phase, 36 participants were randomized 1:1:1 to immediate (low or intermediate dose) or deferred (control) treatment. The primary outcome was safety. Secondary efficacy outcomes included static perimetry, microperimetry, vision-guided mobility, best corrected visual acuity, and contrast sensitivity. Safety and efficacy outcomes were assessed for 52 weeks for immediate treatment participants and 26 weeks for control participants.

RESULTS

AAV5-hRKp.RPGR was safe and well tolerated, with no reported dose-limiting events. Most adverse events (AEs) were transient and related to the surgical procedure, resolving without intervention. Two serious AEs were reported with immediate treatment (retinal detachment, uveitis). A third serious AE (increased intraocular pressure) was reported outside the reporting period. All ocular inflammation-related AEs responded to corticosteroids. Treatment with AAV5-hRKp.RPGR resulted in improvements in retinal sensitivity and functional vision compared with the deferred group at Week 26; similar trends were observed at Week 52.

CONCLUSIONS

AAV5-hRKp.RPGR demonstrated an anticipated and manageable AE profile through 52 weeks. Safety and efficacy findings support investigation in a phase 3 trial.

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.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Retinitis Pigmentosa: From Pathomolecular Mechanisms to Therapeutic Strategies

Retinitis pigmentosa is an inherited disease, in which mutations in different types of genes lead to the death of photoreceptors and the loss of visual function. Although retinitis pigmentosa is the most common type of inherited retinal dystrophy, a clear line of therapy has not yet been defined. In this review, we will focus on the therapeutic aspect and attempt to define the advantages and disadvantages of the protocols of different therapies. The role of some therapies, such as antioxidant agents or gene therapy, has been established for years now. Many clinical trials on different genes and mutations causing RP have been conducted, and the approval of voretigene nepavorec by the FDA has been an important step forward. Nonetheless, even if gene therapy is the most promising type of treatment for these patients, other innovative strategies, such as stem cell transplantation or hyperbaric oxygen therapy, have been shown to be safe and improve visual quality during clinical trials. The treatment of this disease remains a challenge, to which we hope to find a solution as soon as possible.

Update on gene therapies in pediatric ophthalmology

Rare eye diseases encompass a broad spectrum of genetic anomalies with or without additional extraocular manifestations. Genetic eye disorders in pediatric patients often lead to severe visual impairments. Therefore, a challenge of gene therapy is to provide better vision to these affected children. In recent years, inherited retinal diseases, inherited optic neuropathies, and corneal dystrophies have dominated discussions to establish gene and cell replacement therapies for these diseases. Gene therapy involves the transfer of genetic material to remove, replace, repair, or introduce a gene, or to overexpress a protein, whose activity would have a therapeutic impact. For the majority of anterior segment diseases, these studies are still emerging at a preclinical stage; however, for inherited retinal disorders, translation has been reached, leading to the introduction of the first gene therapies into clinical practice. In the past decade, the first gene therapy for biallelic RPE65-mediated inherited retinal dystrophy has been developed and the FDA and EMA both approved ocular gene therapy. Other promising approaches by intravitreal injection have been investigated such as in CEP290-Leber congenital amaurosis. Various techniques of gene therapies include gene supplementation, CRISPR-based genome editing, as well as RNA modulation and optogenetics. Optogenetic therapies deliver light-activated ion channels to surviving retinal cell types in order to restore photosensitivity. Beyond retinal function, ataluren, a nonsense mutation suppression therapy, enables ribosomal read-through of mRNA containing premature termination codons, resulting in the production of a full-length protein. An ophthalmic formulation was recently evaluated with the aim of repairing corneal damage, pending new clinical studies. However, various congenital disorders exhibit severe developmental defects or cell loss at birth, limiting the potential for viral gene therapy. Therefore mutation-independent strategies seem promising for maintaining the survival of photoreceptors or for restoring visual function. Restoring vision in children with gene therapy continues to be a challenge in ophthalmology. © 2023 Published by Elsevier Masson SAS on behalf of French Society of Pediatrics.

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.

Retinitis pigmentosa GTPase regulator-related retinopathy and gene therapy

Retinitis pigmentosa GTPase regulator (RPGR)-related retinopathy is a retinal dystrophy inherited in a X-linked recessive manner that typically causes progressive visual loss starting in childhood with severe visual impairment by the fourth decade of life. It manifests as an early onset and severe form of retinitis pigmentosa. There are currently no effective treatments for RPGR-related retinopathy; however, there are multiple clinical trials in progress exploring gene augmentation therapy aimed at slowing down or halting the progression of disease and possibly restoring visual function. This review focuses on the molecular biology, clinical manifestations, and the recent progress of gene therapy clinical trials.

Gene therapies in pediatric ophthalmology

Genetic pediatric eye disease frequently leads to severe vision impairment or blindness. Voretigene neparvovec is the first approved gene therapy for an inherited retinal dystrophy (IRD). Voretigene neparvovec has been shown to be well tolerated and safe, with encouraging results in terms of efficacy, mainly when administered early in childhood. While we assisted at the first gene therapy available in clinical practice for an IRD, some questions remain unanswered, especially when gene therapy is delivered in young children. We review here the most recent reports and promising ongoing studies concerning various approaches on gene therapy in pediatric ophthalmology.

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.