 National Academy of Sciences USA" to the analytical and FDTD modeling advances reported in July 2013 in "Physical Review Letters".The latter paper rigorously shows that spectroscopic microscopy permits determining the nature of deeply subdiffraction three-dimensional refractive-index fluctuations of a linear, label-free dielectric medium in the far zone.Using visible light, this means that statistical fluctuations of intracellular media as fine as 20 nm can be characterized.