PurposeTo describe progression of best-corrected visual acuity (BCVA), full-field stimulus thresholds (FST), and electroretinography (ERG) over 4 years in the RUSH2A study and to assess their suitability as clinical trial endpoints. DesignProspective natural history study. ParticipantsParticipants (n=105) with biallelic disease-causing sequence variants in USH2A and BCVA letter score of ≥54 were included. MethodsBCVA, FST, fundus-guided microperimetry, static perimetry and spectral domain optical coherence tomography were performed annually and ERG at baseline and 4 years only. Mixed effects models were used to estimate annual rates of change with 95% confidence intervals (CI). Associations of change from baseline to 4 years between BCVA, FST, ERG and other metrics were assessed with Spearman correlation coefficients (rs). Main Outcome MeasuresBCVA, FST, ERG. ResultsThe annual rate of decline in BCVA was 0.83 (95% CI: 0.65, 1.02) letters/year. For FST, the change was 0.09 (0.07, 0.11) log cd.s/m2/year for white threshold, 0.10 (0.08, 0.12) log cd.s/m2/year for blue threshold and 0.05 (0.04, 0.06) log cd.s/m2/year for red threshold. Changes were 22.6 (17.4, 28.2) %/year for white threshold, 26.0 (20.3, 32.1) %/year for blue threshold, and 12.3 (8.7, 16.0) %/year for red threshold. The high percentage of eyes with undetectable ERGs at baseline limited assessment of change. ConclusionBCVA was not a sensitive measure of progression over 4 years. FST was a more sensitive measure; however, additional information on the clinical relevance of changes in FST is needed before this test can be adopted as an endpoint for clinical trials.
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