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GB 11533-2011 English PDF (GB11533-2011)

GB 11533-2011 English PDF (GB11533-2011)

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GB 11533-2011: [GB/T 11533-2011] Standard for logarithmic visual acuity charts

This Standard specifies the design criteria, printing specification, use methods, and visual acuity statistical methods, etc. of visual acuity charts. This Standard is applicable to general physical examinations for children, adolescents and adults aged 3 years and above, distant and near optometry and visual impairment screening for physical examinations such as enrollment and recruitment. It can also be used for reference in ophthalmology and optometry clinical aspects.
GB/T 11533-2011 (Renamed from GB 11533-2011)
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 13.100
C 56
GB 11533-2011
Replacing GB 11533-1989
Standard for logarithmic visual acuity charts
ISSUED ON: DECEMBER 30, 2011
IMPLEMENTED ON: MAY 01, 2012
Issued by: Ministry of Health of the P. R. China;
Standardization Administration of the P. R. China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Terms and definitions ... 5
3 Design criteria for visual acuity charts ... 9
4 Printing specification for visual acuity charts ... 10
5 Use methods of visual acuity charts ... 12
6 Visual acuity statistics ... 16
7 Others ... 17
Appendix A (Informative) Standard for logarithmic distant visual acuity charts ... 18 Appendix B (Informative) Standard for logarithmic near visual acuity charts ... 19 Standard for logarithmic visual acuity charts
1 Scope
This Standard specifies the design criteria, printing specification, use methods, and visual acuity statistical methods, etc. of visual acuity charts.
This Standard is applicable to general physical examinations for children, adolescents and adults aged 3 years and above, distant and near optometry and visual impairment screening for physical examinations such as enrollment and recruitment. It can also be used for reference in ophthalmology and optometry clinical aspects.
2 Terms and definitions
The following terms and definitions apply to this Standard.
2.1
Optotype
Various characters, numbers, and graphics etc. used to measure visual acuity. 2.2
Visual angle
The angle between two points on the external object at the eye nodal point (N), expressed as ??, in minutes (?€?) (see Figure 1).
Figure 1 -- Schematic diagram of visual angle ?? and nodal point N
2.3
Nodal point, N
Use the 5-mark record method. For each additional line of optotypes above 3.0, the record is added by 0.1, which is arranged in an arithmetical progression. Each line of optotypes can be accompanied by the corresponding decimal record value (approximate value) at the same time.
3.6 Directly measurable range
3.6.1 The visual angle of the maximum optotype of distant visual acuity chart is 10?€?. The visual angle of the minimum optotype is 0.501?€?. The visual acuity of 4.0~5.3 (decimal record 0.1~2.0) can be directly measured.
3.6.2 The visual angle of the maximum optotype of near visual acuity chart is 19.953?€?. The visual angle of the minimum optotype is 0.794?€?. The near visual acuity of 3.7~5.1 (decimal record 0.05~1.2) can be measured directly.
4 Printing specification for visual acuity charts
4.1 Paper
4.1.1 The distant visual acuity chart is printed on offset printing paper. The quantitative weight is more than 70 g/m2. The whiteness is not less than 85%.
4.1.2 The near visual acuity chart is printed on white cardboard. The quantitative weight is more than 200 g/m2. The whiteness is not less than 90%.
4.2 Breadth
4.2.1 The distant visual acuity chart adopts the 5K (777 mm??217 mm) breadth of 787 mm??1092 mm paper. The allowable deviation is ??3 mm.
4.2.2 The near visual acuity chart adopts the 115 mm??105 mm breadth. The allowable deviation is ??2 mm.
4.3 Format
4.3.1 The distant visual acuity chart is arranged with 14 lines of optotypes from top to bottom according to the size. The line spacing is 24 mm. The number of optotypes in each line is shown in Table 2.
Table 2 -- Number of optotypes on the distant visual acuity chart
4.3.2 The near visual acuity chart is arranged with 15 lines of optotypes from top to Number of
optotypes
Visual
acuity
after reflection is 5 m.
5.1.2 The near visual acuity chart shall be placed at 25 cm in front of the examined eye (nodal point) (that is, the standard distance of near visual acuity chart). 5.1.3 In addition to the examine distances specified above, other examine distances can be used for distant and near visual acuity charts; see 5.5.
5.2 Placement height of visual acuity chart
5.2.1 The 5.0-line optotype on the distant visual acuity chart is the same height as the eye to be examined.
5.2.2 The near visual acuity chart is perpendicular to the line of sight of the eye to be examined.
5.3 Lighting of visual acuity chart
Artificial lighting shall be used. If direct lighting is used, the illumination shall not be less than 300 lx. If back-lighting method (visual acuity chart light box or screen display) is used, the luminance of the white background of the visual acuity chart shall not be lower than 200 cd/m2. The lighting shall be uniform, constant, non-reflective and non- dazzling. The visual acuity chart shall be kept out of direct sunlight or strong light. 5.4 Determination of visual acuity
5.4.1 Determination of general visual acuity
According to the general use method of the visual acuity chart, measure the smallest line of optotypes that can be recognized by the examined eye (the number of correctly- recognized optotypes shall be more than half of the total number of optotypes in this line). Record the visual acuity record value of the line of optotypes, which is the visual acuity of the eye.
5.4.2 Determination of extraordinary visual acuity
When the distant visual acuity exceeds 5.3 (2.0), the following method can be used to measure.
When the examinee, in front of the distant visual acuity chart, retreats to a certain examine distance listed on the right side of Table 5, the measured 5-mark record value plus the corresponding emendation (e) is his actual visual acuity.
5.4.3 Determination of low visual acuity
When the visual acuity is less than 4.0 (0.1), the following method can be used to measure:
a) The examinee directly walks to 1 m in front of the distant visual acuity chart. The measured 5-mark record must subtract the emendation 0.7 (that is, the emendation e corresponding to the 1 m examine distance in Table 5). At this time, the distant visual acuity chart can measure the visual acuity of 3.3~4.6 (0.02~0.4); b) When the examinee approaches the distant visual acuity chart to a certain examine distance listed on the left side of Table 5, the measured 5-mark record value plus the corresponding emendation e is his actual visual acuity;
c) The near visual acuity chart is a ready-made low visual acuity chart, which can directly measure visual acuity as low as 3.7 (0.05).
5.5 Variable distance application of visual acuity chart
5.5.1 General principles of variable distance application
According to the site distance, the design distance (see Table 3 and Table 4) of any line of optotypes on the distant and near visual acuity charts of this Standard can be selected as the examine distance. When the design distance of a line of optotypes is selected as the examine distance, the 5-mark record value of the line of optotypes shall be recorded as 5.0. The difference between the original record value of this line and 5.0 is the emendation. The 5-mark record values of the upper and lower lines of optotypes must be corrected one by one with this emendation.
5.5.2 Special cases for variable distance application
5.5.2.1 When using the near visual acuity chart to measure the near visual acuity, the examinee can freely move the examine distance. The measured highest 5-mark record value PLUS the emendation obtained by looking up Table 6 according to the distance IS the actual visual acuity.

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