lens" specifically refers to a subclass of aspheric lens. Designs that feature "flatter" curves trade optical quality for cosmetic appearance. By using a non-spheric lens shape, an aspheric lens attempts to correct the error induced by flattening the lens. Typically, the design focuses on reducing the error (OAE) across the horizontal and vertical lens axis edges. This is of primary benefit to farsighted individuals, whose lenses have a thick center. An atoric lens design refers to a lens with a more complex aspheric lens design. An atoric lens design can address errors over more corners of the lens, not just the horizontal and vertical axis. A toric lens is designed to compensate for the astigmatism of a patient's eye. Even though this lens is technically "aspheric", the terms "aspheric" and "atoric" are reserved for lenses which correct errors induced by cosmetic lens flattening. U.S. legal requirements for prescriptions In the United States, laws at the federal and state level govern the provision and effective dates of prescriptions for contact lenses and eyeglasses. Federal law requires that eyeglass and contact lens prescriptions be given to every consumer and that the prescriptions be for a minimum of one year. (FTC Section 456.2 "Separation of examination and dispensing" was reviewed in 2004: FTC 2004 review of section 456.2). State laws vary. For example, California law also requires prescriptions to be provided to clients whether demanded or not. Eyeglass prescriptions must be for a minimum of two years, and contact prescriptions must be for a minimum of one year. See also Contact lens Dioptre Eyeglass prescription Lorgnette Monocle Photochromic lens Pince-nez Visual acuity References Ophthalmology Optometry