1、BRITISH STANDARD BS 4274-1:2003 Visual acuity test types Part 1: Test charts for clinical determination of distance visual acuity Specification ICS 11.040.70 BS 4274-1:2003 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 13 January 2003 BSI 1
2、3 January 2003 First published 26 January 1968 This revision 13 January 2003 The following BSI references relate to the work on this British Standard Committee reference CH/78/6 Draft for comment 00/560371/DC ISBN 0 580 40644 X Committees responsible for this British Standard The preparation of this
3、 British Standard was entrusted to Technical Committee CH/78/6, Ophthalmic Instruments, upon which the following bodies were represented: Association of British Dispensing Opticians BMA College of Optometrists DoH Medical Devices Agency Federation of Ophthalmic and Dispensing Opticians Federation of
4、 Manufacturing Opticians Flat Glass Manufacturers Association Institute of Mechanical Engineers Medical sterile Products Association Optic (UK) Royal College of Ophthalmologists Amendments issued since publication Amd. No. Date CommentBS 4274-1:2003 BSI 13 January 2003 i Contents Page Committees res
5、ponsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3T e r m s a n d d e f i n i t i o n s 1 4 Requirements 2 5 Environmental conditions 4 6 Electrical safety 5 7L a b e l l i n g 5 Annex A (informative) Conversion of different visual acuity notations 6 Annex B (normative)
6、Letter formats 7 Bibliography 9 Figure B.1 Letter formats 7 Table 1 Range of letter sizes, heights and number of letters per line 3 Table 2 Conditions in use 4 Table 3 Storage conditions 4 Table 4 Transport conditions 4 Table A.1 Conversion of different visual acuity notations 6BS 4274-1:2003 ii BSI
7、 13 January 2003 Foreword This part of BS 4274, which has been prepared for clinical use by Technical Committee CH/78, supersedes BS 4274-1:1968, which is withdrawn. The other parts of BS 4274, which are for non-clinical purposes, are: Part 2: Specification for Landolt ring optotype for non-clinical
8、 purposes (BS EN ISO 8596); Part 3: Method for correlating optotypes used for non-clinical purposes (BS EN ISO 8597). This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does no
9、t in itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to ii, pages 1 to 9 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 4274-1:2003 BSI 13 Janua
10、ry 2003 1 Introduction This British Standard utilizes the logMAR notation (logarithm of the minimum angle of resolution) as opposed to the traditional Snellen notation. Use of the logMAR notation facilitates analysis of visual acuity scores, and changes in such scores, more effectively than other no
11、tations because equal linear steps on the logMAR scale represent equal ratios in the standard size sequence. This minimum standard, which in itself does not represent a full logMAR chart, is intended as a stepped approach to the goal of the introduction of a full logMAR chart. This British Standard
12、takes into account the need for these charts to fit into existing hardware/test cabinets. The physical size of a full logMAR chart would exclude this possibility. Nevertheless, although a full chart exceeds the minimum requirements of this British Standard, this British Standard does not preclude th
13、e use of a full chart. 1 Scope This Part of BS 4274 specifies minimum requirements for test charts and test types employing upright sans-serif capital letters for use in the clinical determination of distance visual acuity. NOTE Unless otherwise indicated by the context, the word “letter” includes,
14、in any orientation, the single letter (Landolt or broken ring) and the single letter (illiterate ). This Part of BS 4274 is primarily intended for clinical measurements but may be used for other purposes such as screening, certification and licensing. It is not applicable to chart projectors, charts
15、 or types designed for specialized use (e.g. crowding symbols, lower case letters, isolated letters, low vision evaluation and contrast sensitivity testing). NOTE This British Standard makes no reference to surrounding luminance because this relates to the conditions in the consulting room or clinic
16、 itself and this is outside the Scope of this British Standard. Nevertheless, the level of surrounding luminance can seriously affect the visual acuity scores obtained, for example, by producing glare or excessive contrast. Attention, therefore, should be paid to the level of surrounding luminance w
17、hen installing and utilizing these test charts. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document applies. BS EN
18、 60601-1:1990, Medical electrical equipment Part 1: General requirements for safety. BS ISO 9022-2:1994, Optics and optical instruments Environmental test methods Part 2: Cold, heat, humidity. BS ISO 9022-3:1994, Optics and optical instruments Environmental test methods Part 3: Mechanical stress 3 T
19、erms and definitions For the purposes of this Part of BS 4274, the following terms and definitions apply. 3.1 Landolt ring character in the form of a letter in any one of the orientations described in 4.9 3.2 letter size distance, measured in metres, at which the height of the letter subtends an ang
20、le of five minutes of arc, expressed as the number only 3.3 limb constituent component of a letter, which may be straight or curved 3.4 line row of lettersBS 4274-1:2003 2 BSI 13 January 2003 3.5 logMAR log minimum angle of resolution logarithm to base 10 of the smallest visual angle (expressed in m
21、inutes of arc) that can be resolved by the subject 3.6 luminance contrast the ratio: 3.7 Snellen notation fraction in which the numerator indicates the test distance, expressed in metres, and the denominator indicates the distance, expressed in metres, at which the limb width of the letter subtends
22、one minute of arc and the letter size subtends five minutes of arc 3.8 test chart test type (non-preferred) optotype (non-preferred) presentation of letters of graduated sizes for the purpose of determining distance visual acuity NOTE The presentation may be by means of a printed chart, projection,
23、electronic display or other means. 3.9 unit length linear distance subtending one minute of arc at the distance indicated by the letter size NOTE This equates to of the height of the letter. 3.10 visual angle angle subtended by the unit length of the letter at the testing distance. 3.11 5 5 letter u
24、pright letter which is capable of being framed tangentially by a square, 5 unit lengths in height and width 4 Requirements 4.1 Range of letter sizes The minimum range of letter sizes shall be from logMAR 0.1 to logMAR 1.0. The minimum graduation of letter sizes shall be in not more than 0.1 logMAR s
25、teps between logMAR -0.1 and logMAR 0.4, and in not more than 0.2 logMAR steps thereafter to logMAR 1.0, as shown in Table 1. NOTE Conversions of different visual acuity notations are given in Annex A. where L 1= luminance of the background L 2= luminance of the test letter. L 1 L 2 L 1 -BS 4274-1:2
26、003 BSI 13 January 2003 3 Table 1 Range of letter sizes, heights and number of letters per line NOTE The letter heights given have been calculated on the basis of a 6 metre testing distance. 4.2 Testing distance The design testing distance shall be not less than 4 m. 4.3 Indication of letter size Th
27、e letter size shall be indicated in Snellen denominator and logMAR notation by figures not more than 3 mm high placed below or at either side of each line. 4.4 Selection of letters The letters employed shall be sans-serif 5 5 letters, the selection being from the following: No letter shall be repeat
28、ed on any one line except for Landolt rings and illiterate s. Letters shall be reversed if the chart is to be viewed via a mirror. NOTE It is recommended that no letter be repeated as either the first or last letter of a line although it is acknowledged that, if the chart carries more than 12 lines,
29、 this will not be possible. 4.5 Spacing of letters The letters on each line shall be evenly spaced and centrally disposed. The gap between letters shall be equal to the width of the letters. The space exposed at the ends of each line, as presented, shall be not less than the limb width of the letter
30、s. 4.6 Spacing of lines Lines of letters shall be separated by a gap not less than the letter height in the smaller line or 20 mm whichever is the smaller. 4.7 Additional lines If additional lines are included, their size shall be in accordance with the logMAR notation (see 4.1). The number of lette
31、rs per line shall correspond to the number of letters in the immediately adjacent larger line, and the selection size and spacing shall conform to the requirements of 4.1, 4.2, 4.3, 4.4 to 4.5. 4.8 Dimensions and styles of letters All letters shall have a limb width of 1 unit length, the clear space
32、 between parallel limbs in a letter being 1 or 3 unit lengths as appropriate. In order to unify letter styles all letters shall conform to the formats given in Annex B. 4.9 Dimensions of Landolt ring characters The overall diameter of each broken ring shall be 5 unit lengths, with a limb width of 1
33、unit length. The length of the break shall be 1 unit, the break being placed in the vertical or in any positions either 90 or 45 from the vertical. There shall be a minimum of four different positions. Letter size Minimum number of letters per line Linear height of letter Tolerance on letter height
34、logMAR Snellen mm mm 1.0 60 1 87.30 1.0 0.8 38 2 55.08 0.5 0.6 24 3 34.75 0.5 0.4 15 4 21.93 0.3 0.3 12 5 17.42 0.3 0.2 9.5 5 13.84 0.3 0.1 7.5 5 10.99 0.3 06 5 8 . 7 3 0 . 2 0.1 4.8 5 7.03 0.15BS 4274-1:2003 4 BSI 13 January 2003 4.10 Dimensions of illiterate characters Each letter shall be of 5 5
35、unit length dimensions, the overall length of the middle bar being 4 unit lengths. The position of the open side of the shall be selected from one of four orientations: top, bottom, right or left. 4.11 Luminance contrast Letters shall be black on a white background. The luminance contrast shall not
36、be less than 0.9. 4.12 Luminance The luminance of the presentation shall be uniform and not less than 120 cd/m 2 . Any variation across the test chart shall not exceed 20 %. 5 Environmental conditions 5.1 Conditions in use When tested as described in BS ISO 9022:Parts 2 and 3, the accuracy of the te
37、st charts shall be maintained under the environmental conditions specified in Table 2. Table 2 Conditions in use 5.2 Storage conditions After being exposed to the conditions specified in Table 3, test charts shall meet the manufacturers specifications and the requirements of this standard under the
38、conditions in use specified in 5.1. Table 3 Storage conditions 5.3 Transport conditions After exposure of the charts in the original packing to the conditions given in Table 4, the test charts shall meet the manufacturers specifications and the requirements of this standard under the conditions in u
39、se specified in 5.1. Table 4 Transport conditions Criterion Environmental condition Temperature +10 C to +40 C Relative humidity 95 % Atmospheric pressure 800 mbar to 1060 mbar a Mains power supply voltage b (20 C) 10 % a 1 mbar = 10 2Pa. b If applicable. Criterion Environmental condition Temperatur
40、e 10 C to +55 C Relative humidity 95 % Atmospheric pressure 700 mbar to 1060 mbar a a 1 mbar = 10 2Pa. Criterion Environmental condition Temperature 40 C to +70 C Relative humidity 100 % Atmospheric pressure 500 mbar to 1060 mbar a Vibration sinusoidal 10 Hz to 500 Hz, 0.5 g Shock 30 g; duration 6 m
41、s Bump 10 g; duration 6 ms a 1 mbar = 10 2Pa.BS 4274-1:2003 BSI 13 January 2003 5 6 Electrical safety All electrically-powered (e.g. illuminated) test charts shall conform to the requirements of BS EN 60601-1:1990. All applicable tests of BS EN 60601-1:1990 shall be carried out in the sequence speci
42、fied within Annex C of that standard. 7 Labelling Test charts for which compliance with this Part of BS 4274 is claimed shall be labelled at least with the following information: a) name of manufacturer or manufacturers logo; b) reference to this standard, i.e. BS 4274-1:2002; c) markings as specifi
43、ed in BS EN 60601-1:1990, as appropriate.BS 4274-1:2003 6 BSI 13 January 2003 Annex A (informative) Conversion of different visual acuity notations Table A.1 provides a means of converting visual acuity data from one notation to another. Table A.1 Conversion of different visual acuity notations Snel
44、len Notation indicating measurement at: Decimal notation Visual angle LogMAR 6 m 5 m 4 m 20 ft (independent of test distance) 6/3.0 5/2.5 4/2.0 20/10.0 2.00 0.50 0.3 6/3.8 5/3.2 4/2.5 20/12.5 1.60 0.63 0.2 6/4.8 5/4.0 4/3.2 20/16 1.25 0.80 0.1 6/6.0 5/5.0 4/4.0 20/20 1.00 1.00 0.0 6/7.5 5/6.3 4/5.0
45、20/25 0.80 1.25 +0.1 6/9.5 5/8.0 4/6.3 20/32 0.63 1.6 +0.2 6/12 5/10.0 4/8.0 20/40 0.50 2.0 +0.3 6/15 5/12.5 4/10.0 20/50 0.40 2.5 +0.4 6/19 5/16 4/12.5 20/63 0.32 3.2 +0.5 6/24 5/20 4/16 20/80 0.25 4.0 +0.6 6/30 5/25 4/20 20/100 0.20 5.0 +0.7 6/38 5/32 4/25 20/125 0.16 6.3 +0.8 6/48 5/40 4/32 20/16
46、0 0.125 8.0 +0.9 6/60 5/50 4/40 20/200 0.10 10.0 +1.0 6/75 5/63 4/50 20/250 0.08 12.5 +1.1 6/95 5/80 4/63 20/320 0.06 16.0 +1.2 6/120 5/100 4/80 20/400 0.05 20.0 +1.3BS 4274-1:2003 BSI 13 January 2003 7 Annex B (normative) Letter formats Figure B.1 Letter formatsBS 4274-1:2003 8 BSI 13 January 2003
47、Figure B.1 Letter formats (continued)BS 4274-1:2003 BSI 13 January 2003 9 Bibliography Standards publications BS 3521, Terms relating to ophthalmic optics and spectacle frames BS 3521-1:1991, Glossary of terms relating to ophthalmic lenses Other publications CONCILIUM OPHTHALMOLOGICUM UNIVERSALE VIS
48、IONS FUNCTIONS COMMITTEE. Visual acuity measurement standards. New York, NY: International Council of Ophthalmology, 1984. BAILEY, I.L., and J.E. LOVIE, New design principles for visual acuity letter charts. Am. J. Optom. Physiol. Opt., 1976, 53(11), 7405.BS 4274-1:2003 BSI 389 Chiswick High Road Lo
49、ndon W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions British Standards are updated by amendment or revision. Users of British Standards
