  The couplings of Higgs particles to two photons are analyzed in the threshold
region, where the Higgs mass is about twice the loop--particle mass leading to
possible bound state formation. The amplitude of the pseudoscalar decay $A\to
\gamma\gamma$ for pseudoscalar masses in the range of $(t\bar t)$--bound state
masses is calculated in leading and next--to--leading order in $\alpha_s$. It
is shown that the real and imaginary parts of the form factor are significantly
different from the lowest order perturbative one.
