Stargardt disease is caused by a defective ABCA4 gene, which affects the processing of vitamin A in the eye and leads to the formation of toxic vitamin A aggregates (called "vitamin A dimers") in the eye. Vitamin A dimers are thought to contribute to vision loss in Stargardt disease. ALK-001 is a chemically-modified vitamin A designed as a replacement of vitamin A. ALK-001 has been changed specifically to prevent the formation of toxic vitamin A dimers in the eye, without altering the normal processing of vitamin A to enable vision.