Variable focal length lenses which have an arbitrarily shaped periphery

Abstract

A variable focal length lens whose peripheral shape can be arbitrarily specified, for use in spectacles, which includes a rigid lens to provide the wearer's distance correction, and a liquid-filled lens bounded by a stretched distensible elastomeric membrane to provide a variable near addition. The liquid, which has a fixed volume, is stored in the field of view between the elastomeric membrane and the rigid lens. Variation of the optical power of the liquid filled lens is achieved by displacement of a membrane support to which the outer periphery of the stretched elastomeric membrane is attached. The shape of the distended membrane is kept substantially spherical, despite the circumference of the membrane being non-circular, by making the free area of the membrane circular. This is accomplished by supporting the membrane on a transparent spacing member which has substantially the same refractive index as the liquid and which includes a circular opening which defines the free area of the membrane. A pair of spectacles is comprised of two variable focal length lenses mounted to a frame with an actuator for adjusting their focal lengths mounted on the frame between the lenses. The actuator is mechanically coupled to the lenses by point contacts which prevent twisting couples from being created in the lens structures.