Oral Metformin for Treatment of ABCA4 Retinopathy

Metformin is commercially produced in immediate and extended release. Participants will receive an immediate release formulation of metformin of 500mg daily at study entry. This dose will be titrated up weekly in 500mg increments to reach a goal of 2000mg daily maximum. Once participants \>=17 years of age reach 2000mg metformin immediate release they will switch to an extended-release formulation (1000mg twice a day by mouth). Participants \>= 17 years of age that cannot tolerate 2000mg will be permitted to reduce their daily dose to a minimum of 1000mg/day. Because metformin extended release is not FDA-approved for children under the age of 17, participants under 17 will remain on the immediate release formulation. For these participants who remain on standard formulation, the maximum tolerated dose between 1000mg and 2000mg/day will be given.