Purpose: To estimate the yearly rate of change of best-corrected visual acuity (BCVA) and the risk of loss 1 line or more over 1 year and to identify risk factors for BCVA loss in patients with Stargardt disease (STGD1). Design: Multicenter, prospective cohort study. Participants: Two hundred fifty-nine patients (489 eyes) with molecularly confirmed STGD1 enrolled at 9 centers in the United States and Europe. Methods: Participants were followed up every 6 months, and data at the baseline and 6- and 12-month visits were analyzed. Best-corrected visual acuity was measured using the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol. Standardized reporting forms were used to collect participants' characteristics and clinical observations. Linear mixed effects models were used to estimate the rate of BCVA loss. Linear models with generalized estimating equations were used to identify risk factors for BCVA loss of 1 line or more over 1 year. Main Outcome Measures: Change in BCVA over 1 year. Results: Cross-sectional analysis at baseline showed that earlier symptom onset and longer duration since onset was associated with worse BCVA. Longitudinal analysis showed no overall significant change of BCVA within 12 months, but the rate of BCVA change was significantly different by baseline BCVA (P < 0.001). The BCVA of eyes with baseline BCVA of 20/25 or better declined at a rate of 2.8 ETDRS letters per year (P = 0.10), eyes with baseline BCVA between 20/25 and 20/70 declined at a rate of 2.3 ETDRS letters per year (P = 0.002), eyes with baseline BCVA between 20/70 and 20/200 declined at a rate of 0.8 ETDRS letters per year (P = 0.08), and eyes with baseline BCVA worse than 20/200 showed a significant improvement of 2.3 ETDRS letters per year (P < 0.001). Overall, 12.9% of eyes lost 1 line or more, and the risk of such BCVA loss was different by baseline BCVA level (P = 0.016). Smoking and vitamin A use was not associated significantly with baseline BCVA, nor with rate of BCVA loss over 1 year. Conclusions: Change in BCVA in STGD1 patients over a 12-month period was small, but varied depending on baseline BCVA. Given the slow change during 1 year, BCVA is unlikely to be a sensitive outcome measure for STGD1 treatment trials with 1 year's duration.
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