Spatial dispersion in Casimir forces: A brief review
  We present the basic principles of non-local optics in connection with the calculation of the Casimir force between half-spaces and thin films.   At currently accessible distances $L$, non-local corrections amount to about half a percent, but they increase roughly as 1/L at smaller separations. Self consistent models lead to corrections with the opposite sign as models with abrupt surfaces. 
R Esquivel-Sirvent, C Villarreal, W L Moch\'an, A M Contreras-Reyes,   and V B Svetovoy