An optical wave equation for scattered light in materials with macroscopic spatial inhomogeneities is presented and analyzed. The equation is applicable to a variety of linear and nonlinear optical interactions in media with intrinsic, induced, or engineered inhomegeneities. While it is valid regardless of the spatial scale of these inhomogeneities, the strongest effect is expected from inhomogeneities of a subwavelength scale size typical for nanostructured optical media.