  With the recent measurements on $\eta_{c}$ and $\eta_{c}^{\prime}$ at CLEO,
Babar and Belle, and with the prospect of finding the $\eta_{b}$ at the
Tevatron, it seems appropriate to have another look at the two-photon decay of
heavy quarkonium from the standpoint of an effective Lagrangian based on local
operator expansion and heavy-quark spin symmetry. In this talk, I would like to
discuss a recent work on the two-photon decay rates of ground states and
excited states of $\eta_c$ and $\eta_b$ using the local operator expansion
approach and heavy-quark spin symmetry and taking into account the
binding-energy. We find that the predicted two-photon width for $\eta_c$ agrees
well with experiment, but the predicted value for $\eta_c(2S)$ is twice larger
than the CLEO estimation. We point out that the essentially model-independent
ratio of $\eta_b$ two-photon width to the $\Upsilon$ leptonic width and the
$\eta_b $ two-photon width could be used to extract the strong coupling
constant $\alpha_s$ .
