The current article presents the results of a study of the effect of single-walled carbon nanotubes carcass defects on their electronic structures and optical properties. The study was carried out using an ab-initio quantum mechanical approach: the pseudo-potential method in the density functional theory (DFT) framework in the local density approximation. It is shown that the defects of a single or double vacancy, and Stone- Wales change the absorption spectrum of nanotubes. This can be expressed in the appearance of absorption in the low-energy region and in the smearing of the absorption peaks corresponding to electron transitions between Van Hove singularities near the Fermi energy.