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 (211, 212), the method comprising: directing measurement light to the transparent optical element; detecting measurement light reflected from at least one location on the first surface of the plane parallel portion; detecting measurement light 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 reflected from at least one location on the first surface of the plane parallel portion; detecting measurement light 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.