Disclosed are materials and methods for treating diseases of the mammalian eye, and in particular, Usher syndrome 1B (USH1B). The invention provides AAV-based, dual-vector systems that facilitate the expression of full-length proteins whose coding sequences exceed that of the polynucleotide packaging capacity of an individual AAV vector. In one embodiment, vector systems are provided that include i) a first AAV vector polynucleotide that includes an inverted terminal repeat at each end of the polynucleotide and a suitable promoter followed by a partial coding sequence that encodes an N-terminal portion of a full-length polypeptide; and ii) a second AAV vector polynucleotide that includes an inverted terminal repeat at each end of the polynucleotide and a partial coding sequence that encodes a C-terminal portion of a full-length polypeptide, optionally followed by a polyadenylation (pA) signal sequence. In another embodiment, the vector system includes i) a first AAV vector polynucleotide comprising an inverted terminal repeat at each end, a suitable promoter followed by a partial coding sequence that encodes an N-terminal portion of a full-length polypeptide followed by a splice donor site and intron and ii) a second AAV vector polynucleotide comprising an inverted terminal repeat at each end, followed by an intron and a splice-acceptor site for the intron, followed by a partial coding sequence that encodes a C-terminal portion of a full-length polypeptide, optionally followed by a polyadenylation (pA) signal sequence. The coding sequence or the intron sequence in the first and second AAV vectors preferably includes a sequence region that overlaps.