[Free-vision refraction determination].

A refraction process is called free vision if the patient's visual field is not restricted at all, or at most by the same amount as when using normal spectacles. Free-vision refraction measurement is performed with the help of virtual lenses, which are real optical images of material lenses. In certain circumstances virtual lenses act as normal optical lenses. The advantage of free-vision refraction measurement lies above all in the fact that remote refraction measurement can also be performed from a distance of less than five meters. Moreover, it permits over-refraction, which enables the duration of the measuring procedure to be shortened considerably.