The nature of the critical behavior in the refractive index n is revisited in the framework of the complete
scaling formulation. A comparison is made with the critical behavior of n as derived from
the Lorentz-Lorenz equation. Analogue anomalies to those predicted for the dielectric constant ε,
namely, a leading |t|2β singularity in the coexistence-curve diameter in the two-phase region and a
|t|1−α along the critical isopleth in the one phase region, are expected in both cases. However, significant
differences as regards the amplitudes of both singularities are obtained from the two approaches.
Analysis of some literature data along coexistence in the two-phase region and along the critical isopleth
in the one-phase region provide evidence of an intrinsic effect, independent of the density, in the
critical anomalies of n. This effect is governed by the shift of the critical temperature with an electric
field, which is supposed to take smaller values at optical frequencies than at low frequencies in the
Hz to MHz range.