  We study the (analytic) finite-size corrections in the Ising model on the
strip with fixed ($+ -$) boundary conditions. We find that subdominant
finite-size corrections to scaling should be to the form $a_k/N^{2k-1}$ for the
free energy $f_N$ and $b_k^{(n)}/N^{2k-1}$ for inverse correlation length
$\xi_n^{-1}$, with integer value of $k$. We investigate the set $\{a_k,
b_k^{(n)}\}$ by exact evaluation and their changes upon varying anisotropy of
coupling. We find that the amplitude ratios $b_k^{(n)}/a_k$ remain constant
upon varying coupling anisotropy. Such universal behavior are correctly
reproduced by the conformal perturbative approach.
