ANSI Z80.23-2018 pdf free download.Corneal Topography and Tomography Systems – Standard Terminology, Requirements
1.1 Scope
This American National Standard applies to instruments, systems and methods that are intended to measure the shape of the cornea of the human eye over a majority of its area. The measure- ments of the anterior and/or posterior surface in local areas may be of curvature and/or three di- mensional topographical measurements of the surface. The measurements may be used to de- rive more global parameters used to characterize the surfaces. Instruments classified as oph- thalmometers or keratometers are not covered by this standard.
1.2 Purpose
This standard defines certain terms that are peculiar to the characterization of the corneal shape so that they may be standardized throughout the field of vision care and have common meaning for all those who have occasion to participate in this area. This standard sets forth minimum requirements for instruments and systems that fall into the class of corneal topographers. This standard sets forth tests and verification procedures that will verify that a system or instru- ment complies with the standard and so qualifies as a corneal topographer or corneal tomogra- pher in the meaning of this standard. This standard sets forth certain tests and verification procedures that will allow the verification of capabilities of systems that are beyond the minimum required for corneal topographers or corneal tomographers.
2 Normative references
The following standard contains provisions that, through reference in this text, constitute provisions
of this American National Standard. At the time of publication, the edition indicated was valid. All
standards are subject to revision, and parties to agreements based on this American National
Standard are encouraged to investigate the possibility of applying the most recent editions of the
standards indicated below.
ANSI Z80.20-2004, Ophthalmics – Contact Lenses – Standard terminology, tolerances, meas-
urements and physicochemical properties 1 )
ANSI Z80.28-201 7, Ophthalmic Instruments – Methods for reporting optical aberrations of eyes 1 )
ISO 8429:1 986, Optics and optical instruments – Ophthalmology – Gradual dial scale
ISO 1 01 1 0-1 2:1 997, Optics and optical instruments – Preparation of drawings for optical elements
and systems – Part 12: Aspheric surfaces 1 )
ISO 1 5004-1 :2006, Optics and Optical Instruments – Ophthalmic instruments – Fundamental
requirements and test methods 1 )
IEC 60601 -1 :2006, Medical electrical equipment – Part 1: General requirements for safety 1 )
Foley JD, van Dam A, Finer SK, et al. Fundamentals of Interactive Computer Graphics. Addison-
Wesley, Reading, MA, 1 990
3 Terminology
3.1 corneal apex: The location on the corneal surface, of a normal cornea, where the mean
of the local principal curvatures is greatest.
3.2 corneal eccentricity (e): The eccentricity (e) of the ellipse that best fits the corneal me-
ridian of interest (see 3.9).
If the meridian is not specified, the corneal eccentricity is that of the
flattest corneal meridian (see Table 1 and Annex A).
3.3 corneal meridian (θ): The curve created by the intersection of corneal surface and a
plane that contains the CT axis. A meridian is identified by the angle, θ, that the plane creating it
makes to the horizontal as described by ISO 8429. The value of θ, for a full meridian, takes val-
ues from 0 to 1 80 degrees.
3.3.1 corneal semi-meridian: The portion of a full meridian extending from the CT axis toward
the periphery in one direction. The value of θ for a semi-meridian takes values from 0 to 360 de-
grees.
3.4 corneal shape factor (E): A value that specifies the asphericity and type (prolate or ob-
late) of conic section that best fits a corneal meridian. Unless otherwise specified, it refers to the
meridian with least curvature (flattest meridian) (see Table 1 and Annex A).
3.5 corneal topographer: An instrument or system that measures features of the corneal
surface of living human eyes in a noninvasive manner by using reflected images from the precor-
neal tear film.
Such an instrument is also referred to as a videokeratographer.
