Censoring the Floor Effect in Long-Term Stargardt Disease Microperimetry Data Produces a Faster Rate of Decline

Purpose: To evaluate progression rate estimation in long-term Stargardt disease microperimetry data by accounting for floor effect. Design: Cohort study. Subjects: Thirty-seven subjects (23 females, 14 males) with biallelic ABCA4 pathogenic or likely pathogenic variants and more than >2 years of longitudinal microperimetry data. Methods: Cross-sectional and longitudinal microperimetry data (Grid A: 18° diameter, Grid B: 6° diameter; Macular Integrity Assessment microperimeter, dynamic range 0–36 decibels [dB]) was extracted from patients with biallelic mutation in the adenosine triphosphate-binding cassette subfamily A member 4 (ABCA4) gene. For each eye, mean sensitivity (MS) and responding point sensitivity (RPS) rates were extracted. Floor censored sensitivity (FCS) progression rate, which accounts for the floor effect at each locus by terminating calculation when scotoma was observed in 2 consecutive visits, was also calculated. In a subset of eyes with ≥1 scotomatous locus at baseline (Grid A), sensitivity progression of loci around the scotoma (edge of scotoma sensitivity [ESS]) was examined against other progression parameters. Paired t test compared progression rate parameters across the same eyes. Main Outcome Measures: Microperimetry grid parameters at baseline and progression rates. Results: A total of 37 subjects with biallelic ABCA4 mutations and >2 years of longitudinal microperimetry data were included in the study. In Grid A, at baseline, the average MS and RPS were 16.5 ± 7.9 and 19.1 ± 5.7 dB, respectively. Similar MS (18.4 ± 7.6 dB) and RPS (20.0 ± 5.5 dB) values were found at baseline for Grid B. In Grid A, overall, MS, RPS, and FCS progression rates were −0.57 ± 1.05, −0.74 ± 1.24, and −1.26 ± 1.65 (all dB/year), respectively. Floor censored sensitivity progression rate was significantly greater than the MS or RPS progression rates. Similar findings were observed in Grid B (MS −1.22 ± 1.42, RPS −1.44 ± 1.44, FCS −2.16 ± 2.24, all dB/year), with paired t test again demonstrated that FCS had a significantly faster rate of decline than MS or RPS. In patients with progression data in both grids, MS, RPS, and FCS progression rates were significantly faster in the smaller Grid B. In 24 eyes with scotoma at baseline, fastest rate of decline was ESS combined with FCS compared with other progression parameters. Conclusions: Incorporation of FCS can reduce confound of floor effect in perimetry analysis and can in turn detect a faster rate of decline. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.