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 x 4 phase (As-rich) is obtained after annealing the sample at 340 degreesC (10 mins), while a subsequent annealing at 450 degreesC (15 mins) yields a 4 x 2 phase (In-rich). Using Kramers-Kronig relations, the anisotropy of the imaginary part of the surface dielectric function (Delta epsilon (s)") between [(1) over bar 10] and [110] directions of the substrate has been obtained from RAS data. We present both the RAS and Delta epsilon (s)" spectra characteristic of (2x4) and (4x2) 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-o' bulk critical point (at 4.4 eV) is visible.