[en] Ternary electrooptic oxides, with structures related to that of the perovskite, are used or being considered for potential utilization in optoelectronics technology. Apart from their electrooptic properties, some of these oxides present interesting photochromic and photorefractive effects during illumination. This latter effect is recently an object of much attention because of its relevance to signal and image amplification, reversible holographic storage, real time image processing and conjugated optics. It consists of a reversible light induced charge of refractive index caused by charge redistribution via the electrooptic coupling. Photo-chromic or photorefractive properties critically depend on the occurrence of appropriate centres, either impurities or lattice defects, as well as on suitable carrier transport processes. In this paper, the emphasis lies on recent developments about the defects introduced by doping, thermo-chemical reduction and irradiation