Reflectance anisotropy spectroscopy (RAS) was applied to study the reconstructed surfaces of InAs(001) at room temperature. Arsenic-capped InAs samples, grown by molecular beam epitaxy, were annealed in ultrahigh vacuum. Low energy electron diffraction shows that, following As decapping, a $2\ifmmode\times\else\texttimes\fi{}4$ phase (As-rich) is obtained after annealing the sample at 340 \ifmmode^\circ\else\textdegree\fi{}C (10 mins), while a subsequent annealing at 450 \ifmmode^\circ\else\textdegree\fi{}C (15 mins) yields a $4\ifmmode\times\else\texttimes\fi{}2$ phase (In-rich). Using Kramers-Kronig relations, the anisotropy of the imaginary part of the surface dielectric function $(\ensuremath{\Delta}{\ensuremath{\varepsilon}}_{s}^{\ensuremath{''}})$ between [1\ifmmode\bar\else\textasciimacron\fi{}10] and [110] directions of the substrate has been obtained from RAS data. We present both the RAS and $\ensuremath{\Delta}{\ensuremath{\varepsilon}}_{s}^{\ensuremath{''}}$ spectra characteristic of $(2\ifmmode\times\else\texttimes\fi{}4)$ and $(4\ifmmode\times\else\texttimes\fi{}2)$ reconstructed InAs(001) surfaces, and interpret the appearing features in terms of surface-state transitions and bulk transitions (modified by the surface). The experimental data are compared with the case of GaAs(001). Below 3 eV, the presence of As and In dimers at the surface gives rise to optical anisotropies centered at 2.4 and 1.7 eV, respectively, with opposite polarizations depending on the dimer-bond direction. At higher energies, a structure related to ${E}_{0}^{\ensuremath{'}}$ bulk critical point (at 4.4 eV) is visible.