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New Bi-Sign Aspheric IOL and Its Application

Purpose. To present a bi-sign aspheric intraocular lens (IOL) and make theoretical comparisons with spherical and one-sign aspheric IOLs for retinal image quality in mesopic conditions and intermediate image capability in photopic conditions. Methods. Using ray-tracing in pseudophakic eye models, retinal image quality in terms of modulation transfer function was analyzed between the bi-sign aspheric and three types of one-sign aspheric IOLs and the spherical IOL for the range of corneal asphericities and different lens misalignments at 5 mm pupil diameter; comparison is made with the spherical IOL at defocus conditions characterized by negative refractive errors at 3 mm pupil diameter. Results. Retinal image quality of the bi-sign aspheric lens was equal to or exceeded the one-sign aspheric and spherical IOLs in the majority of anterior cornea asphericities and lens misalignments within the spatial frequencies of 6 to 15 c/deg. Intermediate image capability of the bi-sign aspheric exceeded the spherical IOL. Conclusions. A new bi-sign aspheric lens produces regions of opposite spherical aberrations in the eye model with pupil diameters above 3 mm to balance out aberrations within the lens itself in addition to compensating corneal aberration as with a one-sign aspheric lens. This allows reduction in the variability of the retinal image quality at different anterior cornea asphericities and lens misalignments, when compared with a one-sign aspheric and spherical lens. The bi-sign aspheric produces positive longitudinal spherical aberration in the eye model within 3 mm pupil diameter that improves intermediate image capability when compared with the spherical IOL.