The present invention comprises a lens with variable refraction power as well as an optical system for the use as, preferably accommodating, visual aid. The lens is designed as an intraocular lens or as a contact lens. The general idea of the invention is to determine the accommodation requirement from the position of the eyes relative to one another. This is possible, since the accommodation requirement and the eyes' motor activity are closely related. According to a first embodiment, the present invention claims a lens with variable refraction power, which possesses the following components: means for adaptation of the refraction power, especially by a change of the lens' curvature as a reaction to a control signal; at least one position locator; means for detection of the relative position of the position locator to at least another position locator arranged on another lens; means for generation of the control signal for adaptation of the refraction power of the lens to the detected relative position and at least one device for power supply for at least parts of the components of the lens.