The reflectivity spectra of representative glasses were analyzed to obtain their uv absorption spectra. From these, we show that the first few inverse moments of the absorption give a good representation of the refractive index for visible light when used with the generalized Cauchy dispersion formula [Radiat. Eff. Def. Sol. 157 (2002) 823]. The absorption spectra also illustrate the roles of modifier ions in determining the visible refractive index. These include introduction of ion-specific absorptions (uv color centers); broadening, shifting and altering the strength of glass-former absorptions; and alteration of the density and structure of the glass' random network.