Purpose To determine fixation location and fixation stability in Stargardt disease (STGD1) and their association with best-corrected visual acuity (BCVA). Design Cross-sectional analysis within the multicenter, prospective ProgStar study. Participants A total of 238 patients and 440 eyes with ABCA4-related STGD1. Methods Patients underwent testing with the Nidek MP-1 microperimeter (Nidek Technologies Inc., Gamagōri, Japan). Fixation location was expressed as the eccentricity of the preferred retinal locus (PRL) from the anatomic fovea, fixation stability was expressed as the bivariate contour ellipse area (BCEA), and BCVA was expressed as Early Treatment Diabetic Retinopathy Study (ETDRS) letters. Linear models with generalized estimating equations were used for statistical analysis while accounting for between-eye correlations. Main Outcome Measures Fixation location and fixation stability. Results Median PRL eccentricity from the fovea was 6° (mean, 6.3°; range, 0°–25°) and median BCEA was 6.31°2 (mean, 12.31°2; range, 0.03°2–365.63°2). Each year of later onset of symptoms of STGD1 was associated with 0.14° more central fixation location (P < 0.0001), but not with fixation stability (P = 0.53). A single linear model best described the relationship between fixation location and BCVA: 1° farther PRL eccentricity was associated with a 2.3-letter loss of BCVA (P < 0.0001). A piecewise linear model best described the relationship between fixation stability and BCVA: for a BCEA less than 2.8°2, an increase in BCEA by 1°2 was associated with a 10.5-letter (ETDRS) lower BCVA (P < 0.0001). For a BCEA 2.8°2 or more, an increase in BCEA by 1°2 was associated with a 0.036-letter (ETDRS) lower BCVA (P = 0.0234). Pearson correlation coefficients between patients' right and left eyes were 0.89 (P < 0.0001) for fixation location and 0.25 (P = 0.0006) for fixation stability. After 10 years of disease duration, 82% of patients had eccentric PRLs in both eyes. Conclusions We provide the first extensive database of continuous fixation parameters in STGD1 and demonstrate their association with vision. These measures allow for a more comprehensive assessment of retinal function and may serve as potential secondary outcome measures for future treatment trials for STGD1 and other macular diseases.
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