  We discuss the measured partial width of the pseudoscalar charmonium state
eta_c into two photons. Predictions from potential models are examined and
compared with experimental values. Including radiative corrections, it is found
that present measurements are compatible both with a QCD type potential and
with a static Coulomb potential. The latter is then used to give an estimate on
the eta_b decay into two photons. Results for eta_c are also compared with
those from j/psi data through the NRQCD model.
