  A random matrix model for lattice QCD which takes into account the positive
definite nature of the Wilson term is introduced. The corresponding effective
theory for fixed index of the Wilson Dirac operator is derived to next to
leading order. It reveals a new term proportional to the topological index of
the Wilson Dirac operator and the lattice spacing. The new term appears
naturally in a fixed index spurion analysis. The spurion approach reveals that
the term is the first in a new family of such terms and that equivalent terms
are relevant for the effective theory of continuum QCD.
