A gradient-index ophthalmic lens based on Wood's convex pseudo-lens.

Although the Varilux type varifocal has been and still is very popular, research has been carried out on other methods of providing a progressive addition lens. This paper deals with the field of gradient-index optics. It includes a review of the literature related to the production of a gradient-index element and the theoretical analysis of concentric varifocals. A procedure is described to construct a varifocal lens, after that described by Wood in 1905, to produce lenses known as 'non-homogeneous cylinders' or 'pseudo-lenses'. The method is based on a diffusion process, taking place in half of the lens, and creates steps in the refractive index of the material. Experimental data are also given on the change of the spherical and cylindrical power, which indicate that the lens constructed is an optical system having a rotational symmetry in power, around a fixed point.