  We compute the quasinormal frequencies of $d$-dimensional spherically
symmetric black holes with leading string $\alpha'$ corrections in the eikonal
limit for tensorial gravitational perturbations and scalar test fields. We find
that, differently than in Einstein gravity, the real parts of the frequency are
no longer equal for these two cases. The corresponding imaginary parts remain
equal to the principal Lyapunov exponent corresponding to circular null
geodesics, to first order in $\alpha'$. We also compute the radius of the
shadow cast by these black holes.
