The Effect of Attention on Fixation Stability during Dynamic Fixation Testing in Stargardt Disease

Sensitive, reproducible visual function biomarkers are necessary to evaluate the efficacy of emerging treatments for Stargardt disease type 1 in clinical trials. We previously demonstrated that fixation stability may serve as a secondary outcome parameter for visual function loss. However, the test duration and protocol have an unknown effect on the assessment of fixation stability. Here, we hypothesize that separate fixation testing with a single target is different from combined fixation testing using the same target with simultaneous perimetry testing. International, multicenter, prospective cross-sectional study. Microperimetry data (MP-1, Nidek Technologies) from the international, multicenter, prospective Progression of Atrophy Secondary to Stargardt Disease (ProgStar, NCT01977846) study were analyzed. Patients underwent various types of fixation testing including static testing, dynamic testing, and a duration-corrected dynamic test was generated (30sEpoch). A total of 437 eyes from 235 patients were included (mean age, 33.8 ± 15.1 yrs; 55.3 % female). The mean 1SD-BCEA (Bivariate Contour Ellipse Area), which is the smallest ellipse encompassing 1 standard deviation of all fixation events, was smaller for the static fixation test compared to the 30sEpoch (4.5± 6.9 deg 2 vs. 5.3± 7.0 deg 2 ; P =0.02) and the number of points within both the 2° and 4° circles was larger ( P <.0001). Our results suggest that differences in static and dynamic assessment of fixation stability are not only dependent on different test durations but also on the testing protocol of a single fixation target versus fixation target plus simultaneous perimetry testing and provide information on the conduct of fixation testing for clinical trials.