Lorenz B, et al. – Spatially resolved functional assessment of rods and cones under photopic and scotopic conditions is desirable to assess the treatment outcome of gene therapeutic applications in inherited retinal disorders, for example, early– onset severe retinal dystrophy (EOSRD) or achromatopsia. In the present study, residual vision was cone mediated both under photopic and scotopic conditions in young patients with EOSRD related to RPE65 mutations, but S cone function was severely decreased early on. In rod monochromats, the vision was rod mediated both under conditions of dark and light adaptation. These observations are important for ongoing and future clinical trials employing gene therapeutic strategies in both rod–cone dystrophies and achromatopsia.