The Optical Hawaiian Array for Nanoradian Astronomy (OHANA) will allow resolutions on the order of a fraction of a milliarcsecond in the near infrared. This corresponds to the suspected size of the Broad Line Region and might even allow to study the structure of the base of jets. Preliminary studies with baselines on the order of or greater than 200 meters will be needed to understand these complex objects and successively refine existing models. The continuum visibilities will distinguish any unresolved source from resolved ones. Spectrally resolved visibilities in the H band and in Paschen lines will directly test competing models for the velocity structures that produce the observed line broadening. According to the unified model, the results of these measurements may be expected to depend on the relative viewing geometry. In Phase II, OHANA will be able to select, from many dozens of candidate sources, those most likely to present distinctive differences. A preparatory survey with adaptive optics is already under way. Four different scientific cases involving the OHANA array are reviewed: Active Galactic Nuclei geometries, Broad Line Region tomography, Broad Line Region dynamics, absolute distance measurements with Active Galactic Nuclei.