The present invention relates toa Crumbs homologue (CRB) therapeutic for use as a medicament or in a method of treatment or prophylaxis, for example in the treatment or prophylaxis of a retinal disorder due to mutations in the Crumbs homologue-1 (CRB1)gene, such as Lebers congenital amaurosis 8(LCA8) or retinitis pigmentosa 12 (RP12).In particular, the present invention relates to a recombinant viral vector comprising CRB2 or modified non-toxic forms of either CRB1or CRB3 that resemble CRB2.