  We propose a general method for the numerical evaluation of OPE coefficients
in three dimensional Conformal Field Theories based on the study of the
conformal perturbation of two point functions in the vicinity of the critical
point. We test our proposal in the three dimensional Ising Model, looking at
the magnetic perturbation of the $<\sigma (\mathbf {r})\sigma(0)>$, $<\sigma
(\mathbf {r})\epsilon(0)>$ and $<\epsilon (\mathbf {r})\epsilon(0)>$
correlators from which we extract the values of
$C^{\sigma}_{\sigma\epsilon}=1.07(3)$ and
$C^{\epsilon}_{\epsilon\epsilon}=1.45(30)$. Our estimate for
$C^{\sigma}_{\sigma\epsilon}$ agrees with those recently obtained using
conformal bootstrap methods, while $C^{\epsilon}_{\epsilon\epsilon}$, as far as
we know, is new and could be used to further constrain conformal bootstrap
analyses of the 3d Ising universality class.
