We investigated the crystal structures and optical properties of Ba(M,Mg,Ta)O-3, Ba(M,Zn,Ta)O-3, and Ba(M,Mg,Nb)O-3 (M=Ti, Sn, Zr, and Hf) transparent ceramics. Tetravalent cation substitution resulted in a reduction in the 1:2 order structure of the B-site of the parent perovskites; this in turn led to an increase in the transmittance of the ceramics. There was an increase in the refractive index of Ba(Mg1/3Ta2/3)O-3 due to Ti, Zr, and Hf substitution at the B-site; the refractive index was particularly high in the case of Ti substitution. Furthermore, Ti substitution resulted in a significant decrease in the Abbe number of Ba(Mg1/3Ta2/3)O-3. The refractive index of the perovskites was calculated with high accuracy using the Gladstone-Dale relation. We hypothesize that the Abbe number of perovskites is dependent on its band-gap energy.