GB 11533-2011Standard for logarithmic visual acuity charts (English PDF)

Foreword

3.1, 3.2, 3.3, 3.4, 3.5, 4.1, 4.3.2, 4.3.4, 5.2, 5.3, 5.6.1 of this Standard are mandatory.

The rest are recommended.

This Standard replaces GB 11533-1989 "The standard logarithmic visual acuity charts".

Compared with GB 11533-1989, the main changes of this Standard are as follows.

- Revise the Scope (Clause 1 of the 1989 edition; Clause 1 of this edition).

- Add the term and definition "Logarithm record" (2.13 of this edition).

- Modify the provisions on the maximum optotype size, the minimum optotype size, and the measurable range of near visual acuity charts (3.6.2 of the 1989 edition;

3.6.2 of this edition).

- Modify the provisions on the breadth of near visual acuity charts (4.2.2 of the 1989 edition; 4.2.2 of this edition).

- Modify the number of optotypes in the first line of distant visual acuity charts (Table 2 of the 1989 edition; Table 2 of this edition).

- Modify the provisions on the number of lines of optotypes, the number of optotypes per line, and the line spacing of near visual acuity charts (4.3.2 and Table 5 of the 1989 edition; 4.3.2 and Table 4 of this edition).

- Delete the table to express the number of optotypes and line spacing of near visual acuity charts (Table 3 of the 1989 edition).

- Add requirements for the orientation of adjacent optotypes (4.3.4 of the 1989 edition; 4.3.4 of this edition).

- Modify the record values on both sides of distant and near visual acuity charts AND other printing requirements (4.3.5, 4.3.6, 4.3.7 of the 1989 edition; 4.3.5 and 4.3.6 of this edition).

- Add another regulation on the use method of distant visual acuity charts (5.1.1 of the 1989 edition; 5.1.1 of this edition).

- Modify the provisions on the lighting of visual acuity charts (5.3 of the 1989 edition;

5.3 of this edition).

- Delete a method for the determination of extraordinary visual acuity (5.4.2.2 of the 1989 edition).

- Modify the minimum value that can be measured by the near visual acuity chart [5.4.3.3 of the 1989 edition; 5.4.3.b) of this edition)].

- Modify the table for variable distance correction of near visual acuity chart (Table 7 of the 1989 edition; Table 6 of this edition).

- Delete two methods of special cases for variable distance application (5.5.2.2 and 5.5.2.3 of the 1989 edition).

- Add the informative Appendix "Standard for logarithmic distant visual acuity charts" (see Appendix A).

- Add the informative Appendix "Standard for logarithmic near visual acuity charts" (see Appendix B).

Appendix A and Appendix B of this Standard are informative appendices.

This Standard was proposed by and shall be under the jurisdiction of Ministry of Health P. R. China.

This Standard shall be interpreted by Ministry of Health P. R. China.

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.

Optotype

Various characters, numbers, and graphics etc. used to measure visual acuity.

Visual angle

The angle between two points on the external object at the eye nodal point (N), expressed as alpha, in minutes (') (see Figure 1).

Nodal point, N

The optical center of the eye's refractive system, which is about 7 mm behind the corneal vertex on the optical axis of the eye. When light passes through the nodal point, the direction does not change (see Figure 1).

Examine distance, d' Actual examine distance.

The distance from the visual acuity chart to the eye nodal point (N) of the examinee during the examination. The design distance of all optotypes can be selected as the examine distance in actual use.

2.11

Fraction record

Use the examine distance (numerator) and the design distance (denominator) at the same time to express the visual acuity, namely d/D or d'/D. Its essence is to express visual acuity by the reciprocal of visual angle.

2.12

Decimal record, V

Use the reciprocal of visual angle to express the visual acuity. The unit of visual angle is (') (minute). It is formulated as.

2.13

Logarithm record

Use the logarithm of visual angle to express the visual acuity, i.e. lgalpha.

3 Design criteria for visual acuity charts

4 Printing specification for visual acuity charts

5 Use methods of visual acuity charts

6 Visual acuity statistics

6.1 The visual acuity in 5-mark record can be used for direct comparison of visual acuity level and statistical processing such as visual acuity average, standard deviation, standard error, and significance test. An example is as follows.

6.1.1 The visual acuity comparison can be directly expressed by the number of visual acuity differences (number of lines of optotypes).

6.2 All decimal records, fraction records, and values such as visual angle, optotype size, and design distance cannot be directly compared and counted by the method of 6.1;

7 Others

Other methods of using the visual acuity chart shall comply with the general regulations.

5-mark record