ANSI Z80.20-2016 pdf free download

ANSI Z80.20-2016 pdf free download.Contact Lenses – Standard Terminology, Tolerances Measurements and Physicochemical Properties.
3.5 Apical radius of curvature: The radius of curvature of an imaginary spherical surface having a sagittal depth that is approximately equal to the sagittal depth of the actual aspheric surface in a small area surrounding its apex. 3.6 Aspheric lens: Contact lens with either front or back optic zone having an aspheric surface. 3.7 Aspheric bicurve lens: Contact lens with back surface consisting of two intersecting, concentric, posterior zones of different aspheric surfaces. 3.8 Aspheric multicurve lens: Contact lens with back surface consisting of more than three intersecting, concentric posterior zones of different aspheric surfaces. 3.9 Aspheric surface: A surface that is symmetric about its axis of rotation, in which the radius of curvature varies from the apex to the periphery of the surface. Most aspheric surfaces in the contact lens field are conoidal surfaces derived from conic sections, each having an eccentricity (e) and apical radius of curvature that specify the surface. . 3.10 Aspheric tricurve lens: Contact lens with back surface consisting of three intersecting, concentric posterior zones of different aspheric surfaces. 3.11 Axial edge lift (Iae): Distance from a point on the back surface of a lens at the edge and the vertex sphere, measured parallel to the lens axis. This value is often computed by the manufacturer on the basis of an uncut edge and may be altered by the edging process. 3.12 Axial edge thickness (ae): The axial thickness at the extremity of the peripheral zone (edge) of a contact lens. This value is often computed by the manufacturer on the basis of an uncut edge and may be altered by the edging process. 3.13 Axial lift: Distance from a specified point on the back surface of a lens and the vertex sphere measured parallel to the lens axis. 3.14 Axial thickness: Thickness between the front and back surfaces of a contact lens at a specified position, measured parallel to the lens axis.
3.19 Back peripheral optic zone radius (/x): Where X is one less than the number of back peripheral zones): The radius of curvature of the posterior peripheral zone of a tricurve or multicurve contact lens; a term synonymous with the secondary curve radius of a bicurve lens and then designated 1r. This radius is sometimes called the back peripheral optic zone radius (r) of a concentric back-surface bifocal contact lens, which has two optic zones. 3.20 Back peripheral curve width (中x): Where X is one less than the number of back peripheral zones): The width of the posterior peripheral zone of a multicurve contact lens; a term synonymous with the secondary curve width of a bicurve lens and then designated中1. This dimension is sometimes called the back peripheral optic zone width (中) of a concentric back- surface bifocal contact lens, which has two optic zones. 3.21 Back peripheral zone: The posterior peripheral surface area not contributing to the prescribed optical effect of the optic zone for a single-vision contact lens. This area is sometimes called the back peripheral optic zone of a concentric back-surface bifocal contact lens, which has two optic zones. 3.22 Back secondary curve radius (1): The radius of curvature of the posterior secondary zone of a bicurve, tricurve, or multicurve contact lens; a term synonymous with the back peripheral curve radius of a bicurve lens and the back intermediate curve radius of a tricurve lens, both of which would then also be designated n. Typically, r1 to rn are progressively flatter than ro. For alternative designs, e.g., lenses designed to flatten the cornea, r1 may be steeper than ro 3.23 Back secondary curve diameter or width (中1): The diameter or width of the posterior secondary zone of a bicurve, tricurve, or multicurve contact lens; a term synonymous with the overall diameter or back peripheral curve width of a bicurve lens and the back intermediate curve diameter or width of a tricurve lens, both of which would then also be designated.