The invention relates to a process for designing magneto-optical glasses with zero Verdet constant for manufacturing lenses free of aberration upon operation in magnetic field. The process, as claimed by the invention, consists in using, as vitreous material, aluminophosphatic glass with the composition [0.6 LiPO0.3 Al(PO)0.1 Ba(PO)] which is doped with paramagnetic rare-earth oxides, the Verdet constant for a wavelength within the visible spectrum of 400…700 nm being annulled by selecting a certain dopant molar concentration specific to each type of rare-earth paramagnetic ion, namely: for wavelengths of 405, 465 and 560 nm, the concentrations selected being of 2.10%, 2.25% and 2.45% TbO, respectively, or 2.30%, 2.35% and 2.50 DyO, respectively.