  In this review, we have investigated the asymmetry of the line profile in
precision one- and two-photon spectroscopy of hydrogen and helium atoms within
the framework of a rigorous QED approach. A detailed analysis of the angular
correlations of the quantum interference effect has been carried out using
various examples. Nonresonant effects are also considered in relation to some
astrophysical problems. In particular, a rigorous QED derivation of the
nonresonant extension for the Lorentz line profile is given using the
Ly$_{\alpha}$ transition as an example; such a QED derivation has been lacking
in the literature.
