| 摘要 |
Multifocal lenses are defined by nonconical aspheric optical surfaces. Various alternative surface shapes provide a central distance vision region surrounded by an optical step. The optical step has repidly increasing power in the radial direction which creates an induced aperture through which the cortical elements of the vision system are induced to concentrate. The induced aperture results in increased clarity in distance vision. Nonconical aspheric optical surfaces are defined to produce the desired optical power distributions. These surface functions are also provided in form of polynomial series for simplicity of use in computer driven lathes for shaping contact lenses. To allow increased manipulation of the defining functions additional elements such as conic terms are added. To improve near vision correction in some configurations, an annular near vision region extends radially outward from the optical step. To improve low light distance vision, power is reduced in the lens region outside the mesopic pupillary dimension. In alternative embodiments, the distance vision region and optical step are formed by cyclic functions. These have benefits in ease of manipulation to fit various specific user geometry requirements. In some configurations, an extended near vision region is used outside the optical step to improve near vision correction. The invention includes contact lenses, scleral lenses, intraocular lenses, and lenses impressed or surgically shaped within the corneal tissue as well as methods of designing and fitting these lenses. Although nominally positive power lenses are also within the present invention, negative lenses gain particular benefit due to decreased lens thickness at the lens perimeter and consequent reduced spherical aberration. |
