  Reliable fundamental parameters of open clusters such as distance, age and
extinction are key to our understanding of Galactic structure and stellar
evolution. In this work we use {\it Gaia} DR2 to investigate 45 open clusters
listed in the \emph{New catalogue of optically visible open clusters and
candidates} (DAML) but with no previous astrometric membership estimation based
on {\it Gaia} DR2. In the process of selecting targets for this study we found
that some clusters reported as new discoveries in recent papers based on {\it
Gaia} DR2 were already known clusters listed in DAML. Cluster memberships were
determined using a maximum likelihood method applied to {\it Gaia} DR2
astrometry. This has allowed us to estimate mean proper motions and mean
parallaxes for all investigated clusters. Mean radial velocities were also
determined for 12 clusters, 7 of which had no previous published values. We
have improved our isochrone fitting code to account for interstellar extinction
using an updated extinction polynomial for the {\it Gaia} DR2 photometric
band-passes and the Galactic abundance gradient as a prior for metallicity. The
updated procedure was validated with a sample of clusters with high quality
$[Fe/H]$ determinations. We then did a critical review of the literature and
verified that our cluster parameter determinations represent a substantial
improvement over previous values.
