Purpose
To report visual field loss using static perimetry (SP) and kinetic perimetry (KP) over 4 years in the Rate of Progression of USH2A- related Retinal Degeneration (RUSH2A) study.
Design
Prospective, observational cohort study.
Subjects, Participants, and/or Controls
Participants had USH2A- related rod-cone degeneration, visual acuity ≥20/80, and KP III4e ≥10° at baseline in the study eye. Preserved cohorts with baseline visual fields sufficient to detect progression were identified.
Methods
Participants were examined annually through 4 years. Mixed-effects models were used to estimate the annual, standardized rate, and percentage rates of change.
Main Outcome Measures
SP measures included hill of vision (total: V TOT , central 30°: V 30 , and peripheral: V PERIPH ) and centrally weighted mean sensitivity (MScw). Percentages with 4-year progression exceeding the coefficient of repeatability (CoR) and with change meeting Food and Drug Administration (FDA)-recommended criteria were estimated. KP seeing area (dB-steradian (sr)/degree) for I4e, III4e, and V4e isopters was calculated.
Results
The average decline with SP (95% CI) was 1.94 (1.62, 2.25) dB-sr/y for V TOT , 0.54 (0.45, 0.62) dB-sr/y for V 30 , 1.37 (1.11, 1.63) dB-sr/y for V PERIPH, and 0.56 (0.48, 0.64) dB/y for MS cw . Average percentage decline per year was 8.6% (7.2, 10.0) for V TOT , 6.4% (5.3, 7.5) for V 30 , 13.6% (10.4, 16.7) for V PERIPH , and 5.6% (4.7, 6.4) for MS cw . The standardized rate of change was greatest at −1.35 for MS cw . Rates were higher in the preserved cohorts. Progression exceeding the CoR was 18% (11, 28) for V TOT , 21% (13, 31) for V 30 , 21% (13, 31) for V PERIPH and 17% (10, 27) for MS cw . Progression exceeding an FDA-recommended threshold was 5% (2%, 12%) for all SP points and 45% (35%, 55%) for functional transition points. Average KP annual percentage decline was 13.1% (7.5, 18.5) for I4e, 12.1% (8.1,15.9) for III4e, and 9.2% (6.3,12.0) for V4e.
Conclusions
All quantitative perimetry measures declined over 4 years. Progression was greater than the CoR in a relatively low percentage of eyes (17%-21%); 45% exceeded the FDA-recommended threshold when only functional transition points were considered. Standardized rate of change was greatest for MS cw . These measures are useful characterizations of vision loss in USH2A- related retinal degeneration.
INTRODUCTION
D isease-causing variants in the USH2A gene are among the most common causes of photoreceptor degeneration, either with congenital hearing loss (Usher syndrome type 2, USH2) or as nonsyndromic autosomal recessive retinitis pigmentosa (ARRP). With recent advances in therapeutic approaches, such as antisense oligonucleotides , and gene editing using clustered regularly interspaced short palindromic repeats systems (CRISPR/Cas), several clinical trials have been initiated for USH2A -associated retinal degeneration with additional trials expected. However, several trials for inherited retinal degenerations have recently failed to demonstrate efficacy based on the preselected primary outcome measure, perhaps because prior natural history studies have not investigated quantitative measures of disease progression prospectively and longitudinally over sufficiently long periods to show meaningful change, or due to insufficient treatment effect.
Natural history studies of disease are essential to understand the range of abnormalities that develop in affected individuals and the time course of disease progression. Information from natural history studies informs study design including eligibility criteria and the measures used to assess treatment effects. Although there have been previous studies to characterize the course of disease in affected individuals, little information is available on the natural history derived from more modern methods of ocular imaging and assessment of retinal function.
The Rate of Progression of USH2A -related Retinal Degeneration (RUSH2A) Study was a multicenter, international, longitudinal, observational study to describe disease progression from data collected over 4 years on multiple visual, functional, and structural measures. The design of the RUSH2A study and baseline characteristics of participants have been reported previously. In addition, an interim report on 2-year changes in static perimetry (SP) measures and their association with other measures of retinal function and structure has been published. Here we report annual changes in SP through 4 years and changes in kinetic perimetry (KP) between baseline and year 4, and their association with other measures of retinal function and structure.
METHODS
study design
As described previously, , the RUSH2A study enrolled 127 participants between August 2017 and December 2018 at 16 clinical sites in North America and Europe. The Institutional Review Boards (IRBs) or ethics boards associated with each participating site approved the study, which adhered to the tenets of the Declaration of Helsinki including compliance with the associated federal regulations. Informed consent was obtained from all participants prior to enrollment. The RUSH2A protocol is listed on www.clinicaltrials.gov (NCT03146078) with registration completed prior to enrolling the first participant.
Eligible participants were at least 8 years old with rod-cone degeneration and had at least 2 disease-causing USH2A sequence variants. Genetic reports were reviewed by a committee to confirm the variants as pathogenic or likely pathogenic. Variants in participants with ARRP were further documented as homozygous or heterozygous in trans based on segregation studies . The “study” eye was defined as the eye with better baseline best-corrected visual acuity (BCVA). Participants with a letter score of 54 or greater (20/80 or better) in the study eye, central visual field at least 10 degrees diameter to a III4e target based on KP, and stable fixation at baseline were enrolled in the primary cohort and followed annually over 4 years. Participants with worse visual function were enrolled in the secondary cohort that was studied only at baseline. The 105 participants in the primary cohort were scheduled for annual evaluations in the study eye over 4 years after the baseline visit. Whereas most testing including SP was performed annually, KP was performed only at baseline and 4 years in both eyes. Longitudinal data for participants in the primary cohort were included in this report. Follow-up visits were performed ideally within a ±4-week window of the target annual visit dates (ie, 52, 104, 156, and 208 weeks from baseline visit date), but could occur up to 6 months after the target dates.
perimetry methods
SP was performed on the study eye using the Octopus 900 (Haag-Streit) with the German Adaptive Thresholding Estimation (GATE) strategy and a custom centrally-weighted 186-point grid (historically called 185-point grid, see Supplementary Figure 1) to a size V stimulus ; additional details of testing have been provided previously. SP results were graded by the Casey Reading Center (Casey Eye Institute, Oregon Health Sciences University). A topographic analysis of the SP values was used to generate a three-dimensional, quantitative surface model of the hill of vision. , The total volume, measured in decibel-steradians (dB-sr), beneath the surface of the thin-plate spline representation of the hill of vision within the external boundary of the grid was quantified as V TOT . Additional SP measures included the central 30-degree hill of vision (V 30 ), peripheral hill of vision (V PERIPH ) defined as V TOT minus V 30 , and mean sensitivity (dB) of the centrally-weighted grid (MS CW ). , The average of each SP measure from three repeated SP sessions at baseline was used as the baseline value for analysis.
Semiautomated KP was performed on both eyes for each participant, using the Octopus 900 (Haag-Streit) with EyeSuite software to calculate seeing and nonseeing areas in degree 2 for each isopter and scotoma, respectively; additional details of testing have been provided previously. Six reaction-time vectors were presented within seeing areas, with 1 repetition horizontally, vertically, and diagonally, originating from 10° to 30° eccentricity. Scotomas were mapped at 2°/second angular velocity, with each vector originating from the assumed center. Seeing areas were calculated by subtracting scotomatous areas from the total area for each isopter. The three KP measures analyzed were I4e seeing area, III4e seeing area, and V4e seeing area.
other functional and structural measures
SP and KP were compared with additional measures of visual function or retinal structure. After protocol refraction, BCVA testing was performed using either the electronic visual acuity test protocol or Early Treatment of Diabetic Retinopathy Study (ETDRS) charts with results recorded as the letter score. , Full-field stimulus thresholds (FST) were determined after a 30-minute period of dark-adaptation using white, blue, and red stimuli (Espion E 3 system, Diagnosys LCC). , Fundus-guided mesopic (standard) microperimetry was performed using a Macular Integrity Assessment (MAIA-2) unit (iCare) and summarized by mean sensitivity (MP MS). , The ellipsoid zone (EZ) area and central subfield thickness (CST) were derived from optical coherence tomography (OCT) volume scans (Heidelberg Spectralis HRA+OCT, Heidelberg Engineering GmbH) (described in RUSH2A-4 (MP-OCT)). ,
genetic variant analysis
USH2A variant analysis was performed by two reviewers independently who used the classification system recommended by the 2015 American College of Medical Genetics and Genomics (ACMG) and Association for Molecular Pathology (AMP) guidelines. Each variant was classified as benign, likely benign, variant of unknown significance, likely pathogenic, or pathogenic. Discordant results were resolved by an independent adjudicator.
The number of USH2A truncating alleles was classified as 1, 2, or 3. The following USH2A missense variants with cysteine substitutions were classified as “RP-enriched”: p.Cys759Phe, p.Cys3294Trp, and p.Cys3358Tyr. Participants with one truncating and one missense allele were defined as being in one of two groups: “RP-Enriched” or “Rest” if the missense allele was not RP-enriched, based on the original RUSH2A genetics study.
statistical methods
The analysis cohort for this report was composed of study eyes that had test results for at least 2 of the 5 time points (baseline and 1-4 years) for SP, and/or that had results for both baseline and year 4 for KP. Data from the primary cohort ( N = 105) were included. A total of 103 study eyes met the above criterion for SP analyses and 80 study eyes were included for KP analyses. To mitigate floor effects, a preserved cohort for each SP measure was defined and analyzed separately in addition to the SP analyses using the entire cohort. The preserved cohort for each measure was formed by determining a threshold baseline value above which the slope of the measure over time was greater than 0: V TOT > 5 dB-sr ( N = 91), V 30 > 3 dB-sr ( N = 91), V PERIPH > 5 dB-sr ( N = 79) and SP MS CW > 4 dB ( N = 93).
The distributions of SP measures at each annual visit and the distribution of KP measures at baseline and 4 years were summarized using means, standard deviations (SDs), medians, interquartile ranges (IQRs), and ranges.
For SP outcomes, mixed-effects models with a random intercept were used to estimate the annual rates of change and corresponding 95% confidence intervals (95% CI). Log-transformed data were used to estimate percentage rates of change. Time was calculated as the number of days from baseline divided by 365.25. A model excluding unreliable test results (false positives ≥15%) and a model down-weighting outlier rates of change was also applied to the preserved cohort. For the outlier down-weighted model, the rate of decline for each participant was calculated from a simple linear regression model. A robust regression model using M estimation with a Huber weighting function , was then used to calculate the weight to be applied in the mixed-effects model for each eye in the preserved cohort.
Analyses for estimating annual rates of change of the SP outcomes within subgroups were performed by including time, the baseline subgroup factor, and a term for the interaction between time and the baseline subgroup factor as covariates in the mixed-effects models. Because the baseline level of the SP outcome was associated with the rate of change, it and its interaction term with time were also included in the models for the other baseline subgroup factors. The baseline factors investigated were the baseline value of the outcome, clinical diagnosis, age, disease duration, sex, smoking status, dietary supplement use, truncating group, and RP-enriched allele status. The coefficient of repeatability (CoR) for each SP measure was calculated using data from the 3 repeated SP sessions at baseline, and the proportion of eyes that had a decline exceeding the corresponding CoR from baseline to 4 years was reported (Supplementary Table 1). Using the results from the mixed-effects model applied to the preserved cohort for each measure, a standardized rate of change for each measure was estimated using the following formula: <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='β^’>𝛽ˆβ^
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.
The United States Food and Drug Administration (FDA) has provided guidance on clinically meaningful changes within an eye for SP (mean change of ≥7 dB in ≥5 prespecified points). , The percentages of eyes with changes of these magnitudes were calculated at 4 years. The value of a point at baseline needed to be ≥8 dB to be considered a candidate for a prespecified point. Selection of prespecified points was motivated by results from Hood et al. of a large decrease in sensitivity between adjacent points along a pathway from the center to the periphery as the path crossed from within the EZ to outside the EZ. Functional transition points (FTPs) for SP were identified by comparing each point to 1 to 4 (depending on the location of the point in the testing grid) more peripheral adjacent points on the testing grid. When there was a decrease in sensitivity of ≥7 dB from an inner point to the more peripheral adjacent point, the inner point was qualified as a candidate FTP. In an effort to maximize the likelihood of a candidate FTP losing sensitivity in the future, all candidate FTPs were ordered by the percentage of qualifying adjacent points, from 100% to 25%. Candidate points that were qualified by 100% of adjacent points were selected as an FTP. If the number of selected points was less than 5, then points with next highest percentage of qualifying points were included. Additional approaches for prespecification of points included evaluation of the entire set of points on the testing grid and of the points in the central 30 degrees.
For KP outcomes, change from baseline to 4 years was calculated for each measure. Because distributions for KP measures were extremely skewed, percentage rates of change were calculated using similar mixed-effects models as for the SP measures with natural log-transformed KP data as the dependent variables. Similar subgroup analyses for estimating annual percentage rates of change were also performed for baseline factors.
Associations among change in SP and KP measures and with change in other measures (BCVA, FST, OCT, and MP) from baseline to 4 years were assessed with Spearman correlation coefficients ( r s ). FST testing was done after a 30-minute period of dark-adaptation. All analyses were conducted using SAS version 9.4 (SAS Institute) and reported P values are two-sided.
RESULTS
study population
The number of participants completing baseline and 1- to 4-year annual visits is shown in Supplementary Figure 2. Among the 105 participants recruited into the primary cohort, one participant died before the 1-year visit, one participant died between the 3- and 4-year visits and six additional participants dropped out after the 3-year visit. The number of participants who completed in-office visits for 1, 2, 3, and 4 years is 102, 88, 99, and 95, respectively, for assessment of visual functional and structural measures.
Among the 103 participants included in the SP analyses cohort, the clinical diagnosis was USH2 for 64 (62%) participants and ARRP for 39 (38%) participants. The mean age was 37 years (SD, 12), 58 (56%) were female, and 92 (89%) were white. The median duration of disease at enrollment was 12 years (IQR, 7-20). The baseline characteristics for the 83 participants in the KP analyses cohort were similar.
sp outcomes
The distribution of four SP measures at each visit for the entire analysis cohort is shown in Table 1 and for the preserved cohort is shown in Supplementary Table 2. Figure 1 provides plots of the four SP measures by duration of disease at each visit, showing an overall downward trend over time. At baseline, 13% of participants had V periph values less than 1 dB-sr, a percentage that increased to 17% by 4 years. Among the entire analysis cohort for SP measures [ N = 103], the average V TOT was 32.9 (SD, 23.6) dB-sr at study baseline, which dropped to 29.1 (SD, 22.8) dB-sr at 2 years and 25.2 (SD, 22.3) dB-sr at 4 years. The average V 30 was 10.2 (SD, 5.6) dB-sr at study baseline, which dropped to 9.2 (SD, 5.4) dB-sr at 2 years and 7.9 (SD, 5.1) dB-sr at 4 years. The average V PERIPH was 22.6 (SD, 18.8) dB-sr at study baseline, 19.9 (SD, 18.4) dB-sr at 2 years, and 17.2 (SD, 17.9) at 4 years. The average SP MS cw was 11.6 (SD, 5.8) dB at baseline, 10.6 (SD, 5.5) dB at 2 years, and 9.4 (SD, 5.4) dB at 4 years ( Table 1 ). At baseline, 13% of participants had V PERIPH values less than 1 dB-sr, a percentage that increased to 17% by 4 years.
| Measures | Baseline | Y 1 | Y 2 | Y 3 | Y 4 |
|---|---|---|---|---|---|
| V TOT (dB-sr) | |||||
| N | 103 | 96 | 86 | 99 | 87 |
| Mean ± SD | 32.9 ± 23.6 | 30.9 ± 23.4 | 29.1 ± 22.8 | 27.6 ± 22.8 | 25.2 ± 22.3 |
| Median (IQR) | 29.3 (11.8, 51.2) | 24.5 (11.4, 50.1) | 23.2 (8.5, 47.9) | 19.7 (8.6, 47.8) | 17.1 (7.9, 40.1) |
| V 30 (dB-sr) | |||||
| N | 103 | 101 | 87 | 95 | 91 |
| Mean ± SD | 10.2 ± 5.6 | 9.7 ± 5.5 | 9.2 ± 5.4 | 8.9 ± 5.4 | 7.9 ± 5.1 |
| Median (IQR) | 9.8 (5.4, 14.3) | 9.6 (5.3, 13.7) | 8.2 (4.8, 13.5) | 7.5 (4.5, 13.0) | 6.5 (3.7, 10.7) |
| V PERIPH (dB-sr) | |||||
| N | 103 | 96 | 86 | 99 | 87 |
| Mean ± SD | 22.6 ± 18.8 | 21.0 ± 18.8 | 19.9 ± 18.4 | 18.8 ± 18.2 | 17.2 ± 17.9 |
| Median (IQR) | 18.9 (5.8, 37.7) | 14.6 (4.4, 38.8) | 14.5 (3.5, 33.7) | 11.7 (2.5, 33.2) | 9.0 (2.8, 29.4) |
| SP MS CW (dB) | |||||
| N | 103 | 96 | 86 | 99 | 87 |
| Mean ± SD | 11.6 ± 5.8 | 11.1 ± 5.7 | 10.6 ± 5.5 | 10.1 ± 5.6 | 9.4 ± 5.4 |
| Median (IQR) | 11.0 (6.7, 15.9) | 10.5 (6.9, 14.7) | 9.6 (6.4, 14.2) | 8.6 (5.8, 14.2) | 8.3 (5.2, 12.6) |
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