It has been noted that the family of plane electromagnetic waves and the "electromagnetic universe" of Bertotti-Robinson exhaust the entire class of conformally flat Einsteirr-Maxwell spaces. In the formalism of Newman-Penrose a family of exact solutions of the Einstein-Maxwell equations of the type of Bertotti-Robinson is obtained with a cosmological term belonging to the degenerate type D in the algebraic classification of Petrov and describing the space-time generated by a covariantly constant, nonisotropic electromagnetic field.