1、American National Standardfor Ophthalmics Instruments General-Purpose ClinicalVisual Acuity ChartsANSI Z80.21-2010 (R2015)ANSI Z80.21-2010(R2015)ANSIZ80.21-2010 (R2015)Reaffirmation ofANSI Z80.21-2010American National Standardfor Ophthalmics Instruments General-Purpose ClinicalVisual Acuity ChartsSp
2、onsorThe Vision CouncilApproved May 27, 2010Reaffirmed April 23, 2015American National Standards Institute, Inc.Approval of an American National Standard requires review by ANSI that therequirements for due process, consensus, and other criteria for approval havebeen met by the standards developer.C
3、onsensus 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 unanimity. Consensus requires that allviews and o
4、bjections 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, from manufacturing, marketing, purchasing, or usin
5、gproducts, 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 have the right or authority to issue aninterpretatio
6、n 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 American National Standard may be revised orwithdrawn at
7、 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 calling or writing the AmericanNational Standard
8、s Institute.American National StandardThe Vision Council225 Reinekers LaneSuite 700Alexandria, VA 22314Copyright 2015 by The Vision CouncilAll rights reserved.No part of this publication may be reproduced in anyform, in an electronic retrieval system or otherwise,without prior written permission of
9、the publisher.Printed in the United States of AmericaDeveloped byThe Accredited Committee Z80 for Ophthalmic StandardsThe Vision CouncilZ80 Secretariat225 Reinekers LaneSuite 700Alexandria, VA 22314Published byiContentsPageForeword ii1 Scope and purpose . 12 Normative references. 13 Clinical optotyp
10、e calibration . 24 System requirements 25 Application of standard 36 Marking . 4Table1 Progression of optotypes, in terms of gap size of the equivalent Landolt ring. 5Annexes A Methods of generating correlating optotypes. 6 B Bibliography . 10iiForeword (This foreword is not part of American Nationa
11、l Standard ANSI Z80.21-2010 (R2015).)This American National Standard addresses the optical design of optotypes used inclinical visual acuity measurement systems that use recognition of high-contrast op-totypes and that are designed for general use.ANSI Z80.21-2010 (R2015) was adapted by a group of e
12、xperts within the ANSI Oph-thalmic Instruments Subcommittee under the chairmanship of William L. Brown,O.D., Ph.D. It is a performance standard.There are no substantive changes in this document compared to the previous 2010edition.This standard contains two annexes. Annex A, which is normative, is c
13、onsidered partof this standard. Annex B, which is informative, is not considered part of this stan-dard.Suggestions for improvement of this standard will be welcome. They should be sentto the Vision Council, 225 Reinekers Lane, Suite 700, Alexandria, VA 22314.This standard was processed and approved
14、 for submittal to ANSI by the AccreditedStandards Committee on Ophthalmic Optics, Z80. Committee approval of this stan-dard does not necessarily imply that all committee members voted for its approval. Atthe time of approval of this standard, the Z80 Committee consisted of the followingmembers:Thoma
15、s White, M.D., ChairmanQuido Cappelli, Vice-ChairmanWilliam Benjamin, O.D., SecretaryJeff Endres, SecretariatOrganization Represented Name of RepresentativeAbbott Medical Optics. Leonard BorrmannAdvance Medical Technologies Association Michael PflegerAmerican Academy of Ophthalmology . Dr. Thomas Wh
16、iteAmerican Academy of Optometry. Dr. David LoshinAmerican Ceramic Society Lyle RubinAmerican Glaucoma Society . Dr. Steven GeddeAmerican Optometric Association . Dr. Karl CitekAmerican Society of Cataract and Refractive Ophthalmology Dr. Stephen KlyceContact Lens Institute. Stan RogaskiContact Lens
17、 Manufacturers Association . Quido CappelliDepartment of Veterans Affairs Dr. John TownsendFederated Cornea Societies/ASCRS . Dr. Michael BelinFood the manufacturer should specify the range over which the chart complies with this standard. ANSI Z80.21-2010 (R2015) 4 6 Marking The manufacturer shall
18、provide the following: a) Instructions for setup of the equipment. b) Maintenance required for continued compliance with the requirements of the standard. c) Safety requirements. d) Specification of replacements parts (e.g., lamps) if not supplied by the manufacturer of the original equipment. e) Sp
19、ecifications, including the ranges of visual acuity and luminance conditions within which the instrument complies with the standard. ANSI Z80.21-2010 (R2015) 5 Table 1 - Progression of optotypes, in terms of gap size of the equivalent Landolt ring Exact gap size (min of arc) Snellen fraction for tes
20、t distance Decimal acuity 6 m 5 m 4 m 5.08 m (20 ft) 0.501 6/3.0 5/2.5 4/2.0 20/10.0 2.000 0.631 6/3.8 5/3.2 4/2.5 20/12.5 1.600 0.794 6/4.8 5/4.0 4/3.2 20/16 1.250 1.000 6/6.0 5/5.0 4/4.0 20/20 1.000 1.259 6/7.5 5/6.3 4/5.0 20/25 0.800 1.585 6/9.5 5/8.0 4/6.3 20/32 0.630 1.995 6/12 5/10 4/8.0 20/40
21、 0.500 2.512 6/15 5/12.5 4/10 20/50 0.400 3.162 6/19 5/16 4/12.5 20/63 0.320 3.981 6/24 5/20 4/16 20/80 0.250 5.012 6/30 5/25 4/20 20/100 0.200 6.310 6/38 5/32 4/25 20/125 0.160 7.943 6/48 5/40 4/32 20/160 0.125 10.000 6/60 5/50 4/40 20/200 0.100 12.589 6/75 5/63 4/50 20/250 0.080 15.849 6/95 5/80 4
22、/63 20/320 0.063 19.953 6/120 5/120 4/80 20/400 0.050 ANSI Z80.21-2010 (R2015) 6 Annex A (normative) Method of correlating optotypes A.1 Scope This Annex specifies a method of correlation between a given set of optotypes and the standard optotype (Landolt ring) specified. A.2 General requirements fo
23、r optotypes A.2.1 Each size of a set of optotypes shall be specified in terms of the size of some critical dimension common to that set of optotypes. In the case of the standard Landolt ring, the critical detail is the gap size. In the case of a set of optotypes where there is no dimension common to
24、 the different members of the set (e.g., optotypes for illiterates), the members of a given acuity grade shall have the same relative dimensions as corresponding members of other acuity grades. The size shall be identified by a specified dimension of one member of the set. NOTE 1 If letters or figur
25、es are used for visual acuity measurement, then it should be acknowledged that these normally show large differences in respect of recognizability, even if their size and thickness of stroke are identical. The disadvantages of their use can be reduced by choosing letters or figures that are comparab
26、le with each other. A.3 Correlation of optotypes A.3.1 Selection of optotypes for correlation testing The optotype sizes (grades) specified in the standard shall be used. Sufficient grades or steps shall be used to establish a frequency of seeing curve for the standard optotype and the optotype bein
27、g investigated. A.3.2 Test area The test area shall be circular with a diameter of 4 0.4. The surrounding field shall have a diameter of 15 1.5 and shall be illuminated homogeneously so that it does not influence the measurement. The luminance of the surrounding field shall not be greater than that
28、of the test area. ANSI Z80.21-2010 (R2015) 7 A.3.3 Presentation of the optotypes In making a measurement of visual acuity with the eight-position Landolt ring, 120 presentations shall be made one ring at a time with the ring positions for successive presentations arranged in random order. The optoty
29、pes to be correlated shall also be presented one at a time in random order until a series of 120 presentations has been completed. In the 120 presentations, the different optotypes in each set shall be represented approximately the same number of times. NOTE 2 The number 120 is divisible by 2, 3, 4,
30、 6, 6, 8, 10, 12, 15, 20, 30, 40 and 60. Hence, with sets of optotypes having any of these numbers of different optotypes, it is possible for each optotype to be represented the same number of times in 120 presentations. The comparison must start with a grade of optotypes large enough to yield a fre
31、quency of seeing of 100%. Measurements shall be made with both eight-position Landolt rings and the optotypes of the same size being correlated. When this has been completed, the procedure must be repeated with smaller and smaller sizes until the failure rate corresponds to the level of guessing of
32、0.125. Each optotype must be exposed for 3 s with an interval of 4 s between exposures. NOTE 3 If possible, the comparison of optotypes should be made by means of binocular measurement. A.3.4 Corrective lenses The observers shall be fully corrected to a visual acuity of 1.0 or better, if correction
33、is necessary. A.3.5 Test distance The test shall be performed at a distance of 5 m 0.05 m between the subject and the optotype. NOTE 4 This test distance is for correlation purposes only. A.3.6 Luminance The luminance of the test area shall be 200 cd/m2 50 cd/m2and shall be the same for the Landolt
34、ring as for the optotypes to be correlated. The difference between the luminances of both test areas shall not exceed 10%. The luminance of the optotypes themselves shall not exceed 10% of the luminance of the test area. A.4 Assignment of an acuity score If, before the end of the test, the observer
35、is no longer able to recognize the test types, the subject shall be requested to make a guess. The subject shall not be informed before the end of the test ANSI Z80.21-2010 (R2015) 8 whether or not any mistakes were made. The number of errors per optotype size shall be recorded. From the raw data. a
36、n allowance for guessing shall be made and the frequency of seeing shall be assessed for each optotype size. NOTE 5 The allowance for guessing is performed by the following equation: )1( pNNpRNE= where E is the number of right answers corrected for guessing; N is the number of presentations; R is th
37、e number of right answers; p is the probability of guessing (p is equal to the reciprocal of the number of different optotypes or directions in the set). For the various grades, the frequency of seeing shall be plotted against the logarithm of the size of the critical details. The points on the grap
38、h for each type of optotype shall be fitted with an ogive curve represented by the integral of the probability curve. NOTE 6 Any of the usual methods of fitting the ogive curve may be used. From the curves, the optotype sizes at which the frequency of seeing is 50% shall be estimated, representing t
39、he thresholds for the Landolt ring optotype and the optotype being correlated. From these thresholds the acuity scores shall be derived. A.5 Assessing the equivalence of two kinds of optotype The measurements described in 3.3 shall be repeated with ten or more observers having uncorrected visual acu
40、ity of 1.0 or better, or the observers shall be fully corrected to a visual acuity of 1.0 or better, if correction is necessary. The threshold values for each kind of optotype shall be averaged. NOTE 7 If the two averages differ by more than 0.05 log units, the two sets of optotypes cannot be said t
41、o be equivalent. They can be made equivalent by enlarging or contracting the size of the non-standard optotypes by a factor equal to the ratio of the visual acuity for the nonstandard optotypes to the visual acuity for the standard optotypes. ANSI Z80.21-2010 (R2015) 9 A.6 Significance of the differ
42、ence between the two averages The meaningfulness of the difference between the two averages can be studied by: a) comparing the overlap of the frequency distributions of the two sets of scores; b) using standard statistical procedures to evaluate the significance of the difference between averages;
43、c) plotting a frequency distribution of the differences between the scores on the separate tests to evaluate the tendency to be high or low on both tests; d) using the method of linear regression. ANSI Z80.21-2010 (R2015) 10 Annex B (informative) Bibliography ISO 8596: 1994, Ophthalmic optics Visual
44、 acuity testing Standard optotype and its presentation1)ISO 10938: 1998, Ophthalmic instruments Chart projectors1)Committee on Vision, National Research Council, National Academy of Sciences. Recommended standard procedures for the clinical measurement and specification of visual acuity. Report of W
45、orking Group 39, Washington, DC, 19792). (Also in Advances in Ophthalmology 41, 103-148, 19803)4)Consilium Ophthalmologicum Universal, Visual Functions Committee. Visual acuity measurement standard, 1984) (Also in Italian J. Ophth. II/I, 15, 1988 and Arq. Bras. Oftal. 51(5), 203,1988)4) 1 Available
46、from the American National Standards Institute, 25 West 43rdStreet, New York, NY 10036. 2 Available from the National Academy of Sciences, 2101 Constitution Avenue, NW, Washington, DC 20004. 3 Available from Karger Medical & Scientific Publishing, 27 West Avon Road, Farmington, CT 06085. 4 These standards provide detail and rationale concerning the clinical measurements of visual acuity.
