Non-Orthogonal Refractive Lenses for Non-Orthogonal Astigmatic Eyes

Purpose: To present a novel design method for non-orthogonal lenses to reduce the problem of residual astigmatism in non-orthogonal, astigmatic eyes Methods: A method to create spectacle trial lenses with non-orthogonal power axes was developed based on a novel optimised light ray-tracing algorithm rather than conventional lens design methods which could not fully eliminate spherical aberration. Using this method, three sets of refraction trial lenses were made with the angles between power axes of each set controlled at 80°, 70° and 60°, respectively. Within each set, the cylindrical power varied from -1.00 D to -6.00 D in 1.00 D steps in addition to a -0.50 D lens. Computer-based numerical simulation of the lenses optical performance was carried out to apply orthogonal and non-orthogonal lenses on simulated astigmatic eyes. Subsequently, three clinical trial cases were investigated. Results: Computer-simulated optical performance of non-orthogonal lenses showed the ability to achieve high performance in correcting non-orthogonal astigmatism. Subsequently, three patients with irregular astigmatism were refracted with the non-orthogonal lens sets, and clinically observed improvement at least two lines in the LogMAR chart was achieved in all three cases, compared with correction with orthogonal lenses, along with subjective improvement in image quality. Conclusions: Non-orthogonal astigmatism, which is commonly ignored by current eye prescription systems, is taken into account in this study in the design of spectacle and soft contact lenses. The new approach considers the possible non-orthogonal positions of the eye's two optical power meridians and appears to be better able to correct the vision of irregular astigmatic eyes and significantly reduce residual astigmatism.