The need for affordable and sustainable ophthalmic systems for measurement and correction of refraction is recognized by humanitarian organizations and the scientific community involved in visual optics. Power adjustable optical systems based on transversal lateral movements of two lenses, one with respect to the other, provide a convenient technology for this purpose.
I will review the general theory to understand such systems. There are two types of designs. The first type is a spectacle providing spherical correction, within certain tolerances, over different gaze directions. The second type, recently proposed, is a sphero-cylindrical refractor based on three independent lateral movements of two lenses. Whereas the second type of system permits to set not only sphere but also the cylindrical part of refraction, the optical quality for different gaze directions cannot be optimized as well as for the spectacle with only spherical correction. Overall, both systems can be combined in an integrated strategy. The sphero-cylindrical system could be used to adequately measure refractive errors and then supply very cheap but aesthetically appealing spherical adjustable lenses.
The lenses have a planar and a third-degree polynomial surface. They are arranged with their planar surfaces in contact, so that the incoming light is only refracted by two surfaces. The design goal is to set the shape of these two surfaces. I will explain the methodology used to design these systems.
To show the potentials of the design methodology the optical performance of different examples, as evaluated by numerical simulations, will be presented. Finally, the reliability of manufacturing these systems will be shown with a prototype that was manufactured using free-form machining.
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