  Well-sampled optical light curves of 50 gamma-ray bursts (GRBs) with plateau
features are compiled from the literature. By empirical fitting, we obtained
the parameters of the optical plateaus, such as the decay slopes ($\alpha_{\rm
1}$ and $\alpha_{\rm 2}$), the break times ($T_{\rm b}$), and the corresponding
optical fluxes ($F_{\rm b}$) at the break times. The break time of optical
plateaus ranges from tens of seconds to $10^6$ seconds, with a typical value
about $10^4$ seconds. We have calculated the break luminosity, and it mainly
ranges from $10^{44}$ erg $s^{-1}$ to $10^{47}$ erg $s^{-1}$, which is
generally two or three orders of magnitude less than the corresponding break
luminosity of the X-ray afterglow plateaus. We reanalyzed the optical plateaus
and also found that a significantly tighter correlation exists when we added
the isotropic equivalent energy of GRBs $E_{\rm \gamma,iso}$ into the $L_{\rm
b,z}-T_{\rm b,z}$ relation. The best fit correlation is obtained to be $L_{\rm
b,z}\propto T_{\rm b,z}^{-0.9}E_{\rm \gamma,iso}^{0.4}$. We next explored the
possible correlations among $L_{\rm b,z}$, $T_{\rm b,z}$ and $E_{\rm p,i}$, and
found there is also a tight correlation between them, which takes the form of
$L_{\rm b,z}\propto T_{\rm b,z}^{-0.9}E_{\rm p,i}^{0.5}$. We argue that these
two tight $L_{\rm b,z}-T_{\rm b,z}-E_{\rm \gamma,iso}$ and $L_{\rm b,z}-T_{\rm
b,z}-E_{\rm p,i}$ correlations are more physical, and it may be directly
related to radiation physics of GRBs. The tight correlations are possible to be
used as standard candles.
