  We consider an abstract sequence $\{A_n\}_{n=1}^\infty$ of closed symmetric
operators on a separable Hilbert space $\mathcal{H}$. It is assumed that all
$A_n$'s have equal deficiency indices $(k,k)$ and thus self-adjoint extensions
$\{B_n\}_{n=1}^\infty$ exist and are parametrized by partial isometries
$\{U_n\}_{n=1}^\infty$ on $\mathcal{H}$ according to von Neumann's extension
theory. Under two different convergence assumptions on the $A_n$'s we give the
precise connection between strong resolvent convergence of the $B_n$'s and
strong convergence of the $U_n$'s.
