RecruitingAn Observational Study in Subjects to Follow the Progression of Stargardt Disease Type 1 (STGD1) Caused by Bi-Allelic Autosomal Recessive Mutations in the ABCA4 GeneThis is an Observational Study to Follow the Progression of Stargardt Disease Type 1 (STGD1) Caused by Bi-Allelic Autosomal Recessive Mutations in the ABCA4 Gene This is a multicenter study which will enroll approximately 75 subjects