An autostereoscopic display device (1), includes a display panel (10), a lenticular sheet (15) and an electrically controllable diffuser (80). The electrically controllable diffuser (80) includes an optical medium (94), e.g. polyethyleneterephthalate (PET), with a structured surface (98) against an electro-optic medium (95), e.g. a small droplet polymer dispersed liquid crystal (PDLC) layer. The electro-optic material (95) refractive index is varied with an applied electric field (or zero field) and is switchable between at least (i) a value (n2) substantially matching that of the optical medium (94), which provides a substantially non-diffusing mode, hence 3D operation of the display device, and (ii) a value (n1) different to that of the optical medium (94) hence causing refraction at the structured surface (98), the structured surface (98) providing different refraction angles (.theta..sub.0) so as to provide an overall diffusing effect, hence 2D operation. The diffuser (80) may be provided as a stand-alone item.