The structural, electronic and optical properties of two principal representatives of spinel oxides CdGa2O4 and CdIn2O4 have been investigated using the full-potential augmented plane-wave plus local orbitals method within density functional theory. We used the generalized gradient approximation (GGA) for the exchange-correlation (XC) potential. Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for the band structure calculations. The equilibrium lattice constants and the internal parameters are in agreement with the available experimental results. Results obtained for band structure using GGA-EV show a significant improvement over other theoretical work and are closer to the experimental data. The pressure dependence of band gaps is investigated. The dielectric function, reflectivity spectra and refractive index are calculated up to 50 eV. Pressure and volume dependence of the static refractive index have been also calculated.