  We calculate the critical power for collapse of linearly-polarized phase
vortices, and show that this expression is more accurate than previous results.
Unlike the non-vortex case, deviations from radial symmetry do not increase the
critical power for collapse, but rather lead to disintegration into collapsing
non-vortex filaments. The cases of circular, radial and azimuthal polarizations
are also considered.
