For the sudden loss of central vision? The key to this question might be the composition of the lipofuscin. Based on the Stargardt disease phenotypes and the localization of ABCA4 in the photoreceptor outer segment, it was hypothesized that the lipofuscin that accumulates in Stargardt disease patients might be N-retinylidene-N-retinylethanolamine (A2E) [105, 106, 144], which is the Schiff base rea