A method and apparatus for modelling a lens (104) of an eye (100), comprising: measuring (302) the anterior shape of the eye"s cornea (102) determining (304) direct optical measurements of at least one parameter of the cornea (102) of the eye (100) and at least one parameter of the lens (104) of the eye (100) deterrnining (306) the refractive index of the cornea correcting (308) the optical measurements to account for the effect of the refractive index of the cornea on the direct optical measurements measuring (310) the aberration of the eye calculating (312) the refractive index of the lens by combining the corrected measurements and the aberration and further correcting (314) the optical measurements of the lens to account the effect of the refractive index of the lens on the direct optical measurements.
