  Optical observations of pulsars are crucial to study the neutron star
properties, from the structure and composition of the interior, to the
properties and geometry of the magnetosphere. Historically, X and gamma-ray
observations have paved the way to the pulsar optical identifications. The
launch of Fermi opened new perspectives in the optical-to-gamma-ray studies of
neutron stars, with the detection of more than 80 pulsars. Here, we aim to
search for optical emission from two Fermi pulsars which are interesting
targets on the basis of their spin-down age, energetics, and distance: PSR
J1357-6429and PSR J1048-5832. The two pulsars and their pulsar wind nebulae
(PWNe) are also detected in X-rays by Chandra and XMM. No deep optical
observations of these two pulsars have been reported so far. We used multi-band
optical images (V,R,I) taken with the VLT and available in the European
Southern Observatory (ESO) archive to search for, or put tight constraints to,
their optical emission. We re-assessed the positions of the two pulsars from
the analyses of all the available Chandra observations and the comparison with
the published radio coordinates. For PSR J1357-6429, this yielded a tentative
proper motion mu=0.17+/-0.055 "/yr (70+/-15 deg position angle). We did not
detect candidate counterparts to PSR J1357-6429 and PSR J1048-5832 down to V~27
and ~27.6, respectively, although for the former we found a possible evidence
for a faint, unresolved object at the Chandra position. Our limits imply an
efficiency in converting spin-down power into optical luminosity <7x10^{-7} and
<6x10^{-6}, respectively, possibly close to that of the Vela pulsar.
