Longitudinal Changes of Fixation Stability and Location Within 24 Months in Stargardt Disease: ProgStar Report No. 16

Objective : Stargardt Disease type 1 (STGD1) is the most common macular dystrophy. The assessment of fixation describes an important dimension of visual function but there is limited data on its progression over time. We present longitudinal changes and investigate its usefulness for clinical trials. Design : International, multicenter, prospective cohort study Participants and Main Outcome Measures : A total of 239 individuals with genetically confirmed STGD1 (≥ 1 disease-causing ABCA4 variant). We determined the fixation stability (FS) using the bivariate contour ellipse area (1 SD-BCEA) and fixation location (FL) using the eccentricity of fixation from the fovea during 5 study visits every 6 months. Results : At baseline, 239 patients (105 males, 44 %) and 459 eyes with a median age of 32 years were included. The baseline mean log BCEA was 0.70 ± 1.41 log deg 2 and the mean FL was 6.25 ± 4.40 deg. Although the mean log BCEA did not monotonically increase from visit to visit, the overall yearly increase in log BCEA was 0.124 log deg 2 (95% CI, 0.063-0.185). The rate of change was not different between the two years but increased faster in eyes without flecks outside of the vascular arcades and depended on baseline log BCEA. FL did not change statistically significantly over time. Conclusion and relevance : Fixation parameters are unlikely to be sensitive outcome measures for clinical trials in STGD1 but they may provide useful ancillary information in selected cases to longitudinally describe and understand an eye's visual function.