We present a comprehensive approach for the design of adjustable-focus lenses based on the Alvarez principle. The design methodology consists of dividing the lens into two parts: the inner, optical part, where the optical quality is optimized, and the outer, mechanical part, connecting the optical part to the frame. For the optical part, we present a complete optical design methodology to minimize common optical aberrations, considered in ophthalmic lens design, for different focus adjustments. For the mechanical part, we show how to extend the lens surfaces to connect the optical zone with the frame, such that the entire surface is smooth and has acceptable thickness.