  The wave function of a light pseudoscalar meson is considered and
nonperturbative corrections as signaled by perturbation theory are calculated.
Two schemes are used, the massive gluon and the running coupling scheme. Both
indicate the presence of leading power corrections of ${\cal O}(b^2)$, whose
exponentiation leads to a Gaussian dependence of the wave function on the
impact parameter $b$. The dependence of this correction on the light cone
energy fractions of the quark and the antiquark is discussed and compared with
other models for the meson.
