Optical design of power adjustable sphero-cylindrical ophthalmic systems

Abstract

The need for affordable and sustainable ophthalmic systems for measurement and correction of refraction is well-recognized. Power-adjustable spectacles based on the Alvarez principle (transversal lateral movement of two lenses) have emerged as an innovative technology for this purpose. Within this framework our aim is to design novel power-adjustable ophthalmic systems applying a comprehensive optical design methodology. We present two designs using only two lenses: one is a sphero-cylindrical refractor based on three independent lateral movements. The second system is a spectacle providing spherical correction over different gaze directions. Our optical design methodology comprises several stages. We set a merit function where the oblique astigmatism and mean power error were evaluated for different configurations. The lenses have a planar and a third degree polynomial surface. The lenses are arranged with their planar surfaces in contact, so that the incoming light is only refracted by two surfaces. The merit function was optimized following a cascade approach where different surface parameters where optimized at successive steps. The spherical-cylindrical refractor is capable of measuring sphere powers ranging from -5.00 D to +5.00 D and cross-cylinders from -2.00 D to 2.00 D. The astigmatism and power errors are mostly below 0.1 D in absolute value for all the configurations. We also demonstrate a design for hypermetropia and presbyopia correction with a power variation from +0.5 D to +5 D.