1、AMERICAN NATIONAL STANDARDOLAfor Ophthalmics Corneal Topography Systems Standard Terminology, RequirementsANSI Z80.23-2008ANSIZ80.23-2008ANSIZ80.23-2008(Revision ofANSI Z80.23-1999)American National Standardfor Ophthalmics Corneal Topography Systems Standard Terminology, RequirementsSecretariatOptic
2、al Laboratories Association (until December 31, 2008)The Vision Council (after January 1, 2009)Approved August 4, 2008American National Standards Institute, Inc.Approval of an American National Standard requires review by ANSI that therequirements for due process, consensus, and other criteria for a
3、pproval havebeen met by the standards developer.Consensus is established when, in the judgement of the ANSI Board ofStandards Review, substantial agreement has been reached by directly andmaterially affected interests. Substantial agreement means much more thana simple majority, but not necessarily
4、unanimity. Consensus requires that allviews and objections be considered, and that a concerted effort be madetowards their resolution.The use of American National Standards is completely voluntary; theirexistence does not in any respect preclude anyone, whether he has approvedthe standards or not, f
5、rom manufacturing, marketing, purchasing, or usingproducts, processes, or procedures not conforming to the standards.The American National Standards Institute does not develop standards andwill in no circumstances give an interpretation of any American NationalStandard. Moreover, no person shall hav
6、e the right or authority to issue aninterpretation of an American National Standard in the name of the AmericanNational Standards Institute. Requests for interpretations should beaddressed to the secretariat or sponsor whose name appears on the titlepage of this standard.CAUTION NOTICE: This America
7、n National Standard may be revised orwithdrawn at any time. The procedures of the American National StandardsInstitute require that action be taken periodically to reaffirm, revise, orwithdraw this standard. Purchasers of American National Standards mayreceive current information on all standards by
8、 calling or writing the AmericanNational Standards Institute.American National StandardPublished byOptical Laboratories Association11096 Lee HighwayA101Fairfax, VA 22030-5039Copyright 2008 by Optical Laboratories AssociationAll rights reserved.No part of this publication may be reproduced in anyform
9、, in an electronic retrieval system or otherwise,without prior written permission of the publisher.Printed in the United States of AmericaDeveloped byThe Accredited Committee Z80 for Ophthalmic Standards -Optical Laboratories AssociationZ80 Secretariat11096 Lee HighwayA101Fairfax, VA 22030-5039iCont
10、entsPageForeword ii1 Scope and purpose 12 Normative references . 13 Terminology 24 Requirements . 85 Test methods and test devices. 86 Accompanying documents . 147 Marking. 14Tables1 Conic section descriptors . 72 Test surfaces for type testing . 103 Tolerance levels for test surface measurements 11
11、4 Analysis zones for accuracy and repeatability testing 13Figures1 Illustration of axial curvature, Ka, axial radius of curvature, ra, meridional curvature, Km, and meridional radius of curvature, rm62 Illustration of the corneal vertex and the apex 7AnnexesA Test surfaces for corneal topographers 1
12、5B Standardized displays for corneal topographers 17C Calculation of area weighting values 20D Preprocessing of axial elevation data prior to analysis ofpared data sets. 22iiForeword (This foreword is not part of American National Standard ANSI Z80.23-2008.)This American National Standard continues
13、to address the expressed needs of thosemembers of the ophthalmic community who use corneal topography in clinical set-tings, those who manufacture corneal topographers and those who teach others re-garding the use of the information collected by corneal topographers. In particularthere continues to
14、be a need for standardization of the terms and definitions used inthe field, for standardization of the methods used for characterizing the performanceof these instruments and for standardization of displays of corneal topographical in-formation. The experts who worked together to create this standa
15、rd felt that at thistime there is not sufficient consensus within the ophthalmic community to set perfor-mance requirements for these instruments beyond those for minimum area mea-sured and measurement sample density. The standard continues to addressstandardization of the methods for testing these
16、instruments, for assessing their per-formance, and for reporting the results thus obtained. The number and type of test surfaces to be used has been changed to include onlytest surfaces for which the results can be verified. When these surfaces are tilted orrotated the expected surface measurements
17、are easy to predict. These surfaceswere considered to be adequate as minimum verification surfaces for corneal topog-raphers; if a corneal topography system can measure these surfaces well, it will be aclinically useful instrument. The method for standardization of color maps has beenchanged in an e
18、ffort to improve the users ability to discern just-noticeable-differenc-es in corneal topography. The user always has the option of using a scale with lessresolution but with greater range, as long as the scale recommended in this docu-ment is available to be used.This standard was created by a spec
19、ial working group created by the Z80 Subcom-mittee on Ophthalmic Instruments and included experts in the field of corneal topog-raphy from the clinical, manufacturing and academic areas of the ophthalmiccommunity. This standard contains four annexes. Annex A is informative and is not considered tobe
20、 part of this standard. Annexes B, C, and D are normative and are considered to bepart of this standard.Suggestions for improvement of this standard will be welcome. Prior ro December31, 2008, any comments should be sent to the Optical Laboratories Association, P.O.Box 200, Merrifield, VA 22116-2000
21、. After January 1, 2009, comments should besent to The Vision Council, 1700 Diagonal Road, Suite 500, Alexandria, VA 22314.This standard was processed and approved for submittal to ANSI by the AccreditedStandards Committee on Ophthalmics, Z80. Committee approval of this standarddoes not necessarily
22、imply that all committee members voted for its approval. At thetime it approved this standard, the Z80 Committee had the following members:Thomas White, M.D., ChairmanQuido Cappelli, Vice-ChairmanRobert Rosenberg, O.D., SecretaryDaniel Torgersen, SecretariatOrganization Represented Name of Represent
23、ativeAdvance Medical Technologies Association Douglas J. FortunatoGlenn Davies (Alt.)Bernie Liebler (Alt.)Richard Courtney (Alt.)iiiOrganization Represented Name of RepresentativeAmerican Academy of OphthalmologyThomas C. WhiteGerhard Cibis (Alt.)Norman Lanphear (Alt.)Paul F. Vinger (Alt.)American A
24、cademy of Optometry .David S. LoshinAmerican Ceramic SocietyLyle RubinHerbert Hoover (Alt.)American Glaucoma Society.Steven J. Gedde Douglas J. Rhee (Alt.)American Optometric Association .William L. BrownWilliam J. Benjamin (Alt.)Robert Rosenberg (Alt.)Jeffrey Weaver (Alt.)American Society of Catara
25、ct and Refractive SurgeryStephen KlyceJack T. Holladay (Alt.)Stephen H. Johnson (Alt.)Contact Lens Institute .Tom HenteleffPeter Mathers (Alt.)Contact Lens Manufacturers AssociationQuido CappelliJan Suochak (Alt.)Department of Veterans Affairs.John TownsendSharon R. Atkin (Alt.)Federated Cornea Soci
26、eties .Michael W. BelinDavid Glasser (Alt.)Food ellipse(01). In order to signify use of an oblate curve of the ellipse, e is sometimes given a negative sign that is not used in computations. Otherwise, use of the prolate curve of the ellipse is assumed.3.10 elevation: The distance between the cornea
27、l surface and a defined reference surface, measured in a defined direction from a specified position. 3.10.1 axial elevation: The elevation as measured from a selected point on the corneal surface in a direction parallel to the CT axis. 3.10.2 normal elevation: The elevation as measured from a selec
28、ted point on the corneal sur-face in a direction along the normal to the corneal surface at the point. 3.10.3 reference normal elevation: The elevation as measured from a selected point on the corneal surface in a direction along the normal to the reference surface. 3.11 keratometric constant: The v
29、alue 337.5 used to convert corneal curvature from inverse millimeters (mm -1) to keratometric diopters. 3.12 keratometric diopters: Curvature, in inverse millimeters (mm -1), multiplied by the kera-tometric constant, 337.5. 3.13 meridional plane: The plane that includes the surface point and the cho
30、sen axis. 3.14 normal 3.14.1 surface normal: A line passing through a surface location perpendicular to the plane tangent to the surface at that location. 3.14.2 meridian normal: A line passing through a surface location, perpendicular to the tangent to the meridian curve at the location and lying i
31、n the plane creating the meridian. 3.15 conic parameter (p): A number that specifies a conic section such as an ellipse, a hy-perbola or a parabola. (See table 1.) With a conic section given in the form: 1ab2222=+xzan ellipse or 1ab2222=xz+ a hyperbola ANSI Z80.23-2008the conic parameter is defined
32、by: 22ba=p pE -1=where a and b are constants + indicates an ellipse - indicates a hyperbola The conic parameter of a parabola is zero. 3.16 placido ring target: A target used in corneal topographers consisting of multiple con-centric rings. Each individual ring lies in a plane; however, the rings ar
33、e not in general coplanar. 3.17 radius of curvature: The inverse of the curvature. The units of radius of curvature, for the purpose of this standard, are millimeters. 3.17.1 axial radius of curvature (ra): The distance from a surface point, P, to the axis along the corneal meridian normal at the po
34、int (see figure 1). ra is also defined by the equation: ()xsinxra=where x is the perpendicular distance from the axis to the meridian location millimeters (x) is the angle between the axis and the meridian normal at location x 3.17.2 meridional radius of curvature (rm): rm= 1/Km(see figure 1). 3.18
35、surface 3.18.1 aspheric surface: A nonspherical surface. For corneal topography, a surface with at least one principal meridian that is a noncircular section. For ophthalmic lenses, an axisymmetri-cal surface. 3.18.2 atoric surface: A surface having mutually perpendicular principal meridians of uneq
36、ual curvature where at least one principal meridian is a noncircular section. These surfaces are symmetrical with respect to both principal meridians. 3.18.3 oblate surface: A surface whose curvature increases as the location on the surface moves from a central position to a peripheral position in a
37、ll meridians. 3.18.4 prolate surface: A surface whose curvature decreases as the location on the surface moves from a central position to a peripheral position in all meridians. 3.18.5 reference surface: A surface that can be described in an exact, preferably mathemati-cal fashion, used as a referen
38、ce from which distance measurements are made to the measured corneal surface. In addition to its mathematical description, the positional relationship of the ref-erence surface to the corneal surface shall be specified. For instance, a reference surface might 5 ANSI Z80.23-2008be described as the sp
39、here that is the best least squares fit to the measured corneal surface. Likewise, a plane could serve as a reference surface. 3.18.6 toric surface: A surface for which the principal curvatures are unequal and for which principle meridians are circular sections. Such surfaces are said to exhibit cen
40、tral astigmatism. 3.19 toricity: The difference in principal curvatures at a specified point or local area on a sur-face. 3.20 transverse plane: The plane perpendicular to the meridional plane that includes the normal to the surface point. Figure 1 Illustration of axial curvature, Ka, axial radius o
41、f curvature, ra, meridional curvature, Km, and meridional radius of curvature, rm6 ANSI Z80.23-2008Figure 2 Illustration of the corneal vertex and the apex Table 1 Conic section descriptors Conic Section Conic Parameter, pCorneal Shape Factor, E Eccentricity, e hyperbola p1 e1 parabola 0.0 1.0 1.0 p
42、rolate ellipse 1p0 01 E r1r1- r2= 0.4 0.07 mm accuracy 1 m 10 mm NOTE 1 Surface (1): Verification measurement is possible with a micrometer unit. NOTE 2 Surfaces (2) and (3): An ellipsoid and toric shape can be manufactured by a contact lens company and measured with a 3D-coordinate measuring device
43、. 10 ANSI Z80.23-2008Table 3 Tolerance levels for test surface measurements Tolerances if measurements are expressed in terms of curvature in keratometric diopters Measuring accuracy Type Area center diameter middle diameter outer diameter Twice the standard de-viation A 0.27 0.16 0.16 Twice the sta
44、ndard de-viation B 0.52 0.37 0.37 Tolerances if measurements are expressed in terms of radius of curvature in millimeters Measuring accuracy Type Area center diameter middle diameter outer diameter Twice the standard de-viation A 0.05 0.03 0.03 Twice the standard de-viation B 0.1 0.07 0.07 NOTE Kera
45、tometric diopters are related to radius of curvature given in millimeters by: keratometric diopters = 337.5/radius of curvature. 5.3 Data collection 5.3.1 Test surfaces Align the test surface to the instrument in the manner specified by the manufacturer of the system for measuring human eyes. Measur
46、e the surface and save the measured data. At each meas-ured point, the data set consists of the value of the measured variable and the two-dimensional position of the measurement. 5.3.2 Human corneas Align the instrument to the eye in the manner specified by the manufacturer of the system. Meas-ure
47、the corneal surface and save the measured data. At each measured point, the data set con-sists of the value of the measured variable and the two-dimensional position of the measurement. Move the corneal topographer with respect to the eye and then recenter it. Take a second meas-urement and save the
48、 measured data. 5.4 Analysis of the data The treatment of the corneal topographic data consists of a comparison between the measured values of two data sets. The structure of the data sets is slightly different for the analysis of accu-racy and the analysis of repeatability, so they are given separa
49、tely. 11 ANSI Z80.23-20085.4.1 Structure of the accuracy data set For the purpose of accuracy determination, one data set consists of the measured values and measurement locations from a measurement of a known test surface. The other data set con-sists of the known values of the test surface at the locations measured by the instrument and re-ported as part of the data set. The analysis of the paired sets of data is done in accordance with 5.4.3. 5.4.2 Structure of the repeatability data set For the purpose of repeatability determination, a sample popula
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