When manufacturing a pair of lenses for improving visual performance in patients with keratoconus (a lens here includes a contact lens, an intraocular lens, and a spectacle grass), the following steps are taken for each eye: determining by means of subjective refraction the most effective conventional lens, with equal spherical and cylindrical power over the entire anterior optical zone, determining by subjective refraction optimal optical parameters for a second optical zone applied to the first optical zone, wherein the patient does not have to hold his/her head in a specific position, which optical parameters are formed by the shape, size, value and course of the strength and position on the first optical zone, manufacturing a lens provided with a first and second optical zone as determined above, and repeating the determination of optimal optical parameters for the second optical zone by means of subjective refraction with the lens inserted or in front of it, and producing an adapted lens when deviating optical parameters are found. Then, in or for each eye, one of the fabricated lenses is either presented or inserted and with both eyes looking repeated the subjective refraction determination of optimal optical parameters for the second optical zones for each eye. Thereafter, a set of final lenses having a first and second optical zone as determined above is manufactured.