A young patient present with significant loss of central vision and a normal ERG. There is no obvious family history of similar presentation. The most likely diagnosis -

Loss of central vision along with a normal ERG is consistant with a diagnosis of Best's disease and stargardt's disease. Absence of a positive family history favours a diagnosis of stargardt's disease. Stargardt's disease being an autosomal recessive disorder may not reveal a positive family history. Best's disease, being an autosomal dominant disorder should have a positive family history.