Geometrical optics in twistor space

We formulate the wave vector and the eikonal equation of geometrical optics directly in twistor space. The optical phase is defined as a function on twistor space, from which the space-time wave vector is obtained via the incidence relation. Since the wave vector is constructed as a factorised spinor product, it is null by construction, and the eikonal equation follows identically from the twistor formulation.