A method for determining information about a transparent optical element comprising a lens portion and a plane parallel portion , the lens portion comprising at least one curved surface and the plane parallel portion comprising opposing first and second surfaces , the method comprising: directing measurement light to the transparent optical element ; detecting measurement light (S1) reflected from at least one location on the first surface of the plane parallel portion ; detecting measurement light (S2) reflected from the second surface of the plane parallel portion at a location corresponding to the at least one location on the first surface ; determining, based on the detected light (S1, S2), information about the plane parallel portion , wherein the information about the plane parallel portion comprises information about a refractive index of a material forming the transparent optical element , and either i) wherein the information about the refractive index comprises information about variations of a refractive index between different locations of the plane parallel portion , or ii) wherein the information about the refractive index comprises information about birefringence of the material forming the transparent optical element , and the measurement light (S1, S2, S3, S4) is detected for a first polarization and, thereafter, a second polarization different from the first polarization; and evaluating the transparent optical element based on the information about the plane parallel portion . directing measurement light to the transparent optical element ; detecting measurement light (S1) reflected from at least one location on the first surface of the plane parallel portion ; detecting measurement light (S2) reflected from the second surface of the plane parallel portion at a location corresponding to the at least one location on the first surface ; determining, based on the detected light (S1, S2), information about the plane parallel portion , wherein the information about the plane parallel portion comprises information about a refractive index of a material forming the transparent optical element , and either i) wherein the information about the refractive index comprises information about variations of a refractive index between different locations of the plane parallel portion , or ii) wherein the information about the refractive index comprises information about birefringence of the material forming the transparent optical element , and the measurement light (S1, S2, S3, S4) is detected for a first polarization and, thereafter, a second polarization different from the first polarization; and i) wherein the information about the refractive index comprises information about variations of a refractive index between different locations of the plane parallel portion , or ii) wherein the information about the refractive index comprises information about birefringence of the material forming the transparent optical element , and the measurement light (S1, S2, S3, S4) is detected for a first polarization and, thereafter, a second polarization different from the first polarization; and evaluating the transparent optical element based on the information about the plane parallel portion . <EOS>