Comment about quasi-isotropic solution of Einstein equations near   cosmological singularity
  We generalize for the case of arbitrary hydrodynamical matter the quasi-isotropic solution of Einstein equations near cosmological singularity, found by Lifshitz and Khalatnikov in 1960 for the case of radiation-dominated universe. It is shown that this solution always exists, but dependence of terms in the quasi-isotropic expansion acquires a more complicated form. 
I.M. Khalatnikov, A.Yu. Kamenshchik and A.A. Starobinsky