ISO/DIS 18490:2025(en)

ISO/TC 135/SC 7/WG 10

Secretariat: SCC

Date: 2025-03-05

Non-destructive Testing — Evaluation of vision acuity of NDT personnel

Essais non destructifs — Evaluation de l'acuité visuelle du personnel END

© ISO 2025

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Contents

Foreword iv

Introduction vi

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Chart print quality and marking 2

5 Health and safety requirements 2

6 Personnel administering the test 2

7 Near and Far Vision Test charts 2

8 Test procedure 3

8.1 General 3

8.2 Illumination level (normative) 3

8.3 Luminance (informative) 3

8.4 Eye to chart distance 3

8.5 Vision Correction 3

8.6 The tests 3

9 Acceptance levels 4

Annex A (informative) Radner Chart (Not to scale) 6

Annex B (informative) Snellen Chart (Not to scale) 7

Annex C (informative) Landolt Chart (Not to scale) 8

Annex D (informative) Ishihara Chart (Not to Scale) 9

Annex E (informative) Sample Colour Trade Test Exam 10

Annex F (informative) Corresponding Reading Acuity Notations for Test Distances of 40 cm (16 inches) and 32 cm (12.5 inches) 13

Annex G (informative) Grey Scale Perception Testing 14

Annex H (informative) Low Contrast Visual Acuity 15

Bibliography 16

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

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This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing, SC 7, Personnel Qualification in collaboration with European Committee for Standardization (CEN), in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 18490:2015), which has been technically revised.

The main changes are as follows:

— Far and Colour vision acuity of NDT personnel added to the Scope

— Reference to EN 4179 Aerospace series - Qualification and approval of personnel for non-destructive testing removed

— Reference to ISO 8596:2017 Ophthalmic optics Visual acuity testing Standard and clinical optotypes and their presentation added as informative reference in the bibliography

— Reference to ISO 7921:2024 Ophthalmic optics and instruments- Near reading charts added as informative reference in the bibliography

— Reference to ISO 10938:2016 Ophthalmic optics — Chart displays for visual acuity measurement — Printed, projected and electronic added as informative reference in the bibliography

— Reference to ASTM E3168, Standard practice for Determining Low-Contrast Visual Acuity of Radiographic Interpreters added as informative reference in the bibliography

— New terms and definitions added

— Charts for Illumination level and Luminance added; Chart for Eye to Chart distance for Near, Far and Colour vision added

— Additional provisions for vision correction added

— Test instructions for Near, Far, and Colour vision added

— Informative information for grey scale perception and low contrast acuity added as Annexes (Annex G and Annex H)

— For Near vision removed use of Jaeger Chart and Tumbling E and added use of Reading Charts and Snellen chart

— Acceptance level for Near, Far, Colour visions added

— Examples of Radner, Snellen and Landolt charts added as Annexes

— Corresponding Reading Acuity Notations for Test Distances of 40 cm (16 inches) and 32 cm (12.5 inches) added as Annex

Introduction

Standards for NDT Personnel qualification and certification require that the visual acuity of inspection personnel is verified as being appropriate to their function. By meeting the vision acuity level defined in this International Standard, such requirements of ISO 9712 will be met. The purpose of this International Standard is to provide a detailed, standardised procedure for the evaluation of vision acuity for such personnel under defined lighting conditions.

The tests are not medical in nature and are intended to objectively ensure adequate vision perception without reliance on reading ability or text identification. Because it is extremely difficult to demonstrate any equivalency in vision tests, this International Standard has been prepared in order that an international system may be used without any need to demonstrate equivalence and is the recommended method of determining vision acuity for NDT Personnel.

Non-destructive Testing — Evaluation of vision acuity of NDT personnel

This International Standard specifies the quality requirements for the chart, the test procedure, and the acceptance level for near, far, and colour vision acuity of NDT personnel. Informative information for grey scale perception and low contrast can be found in the annexes. It also addresses the qualification requirements for personnel permitted to carry out the test.

This International Standard only addresses vision acuity under defined conditions similar to those encountered during routine NDT inspection. It does not address an individual’s overall visual acuity and users are advised to consider the need for a general eye examination by specialist medical personnel to ensure general vision acuity.

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel

For the purposes of this document, the terms and definitions given in ISO 9712, ISO 7921, ISO 8596 and the following apply.

3.1

optotype

Letters or symbols shown on an eye chart.

3.2

eyewear

A form of lens or protective transparent material placed or used between the human eye and the work piece during routine NDT inspection operations.

3.3

trade test

A test performed by the employer after failure of the Ishihara Colour test to ensure a candidate can distinguish and differentiate between the colours used in the NDT methods/ techniques concerned as specified by the employer.

3.4

x-height

Height of a lower case “x”, i.e. the middle height of a font.

3.5

logRAD (reading acuity)

Logarithm of “Reading Acuity Determination” which is determined based upon the x-height.

3.6

logMAR (distance acuity)

Logarithm of the “Minimal Angle of Resolution” based upon the opening, or line thickness of a Landolt ring (i.e. one fifth of the optotypes).

3.7

decimal

Reciprocal proportion of the visual angle as calculated from the test distance and one-fifth of the x-height.

3.8

M-Size

Factor used to modify the print size, multiplying it by the letter height at 1 meter (= 1 M- unit).

3.9

N

Desktop Publishing (DTP) point size (1 pt = 1/72 inch) of lower-case letters printed in Times Roman approximately representing correct sizing.

3.10

snellen fraction

Relationship between the test distance in feet and the distance at which an optotype subtends five minutes of an arc (for near vision 1,3/1,3 Snellen for feet or 0,4/0,4 Snellen for meter).

It is recognized that charts produced locally will have varying print quality and resolution. It is recommended that the charts be purchased directly from suppliers or manufacturers and not printed or copied locally. The charts supplied shall be permanently marked with a name or trade name of the manufacturer or supplier, name and model of the chart, reference to documents if the manufacturer or supplier claims conformity with it (i.e. for Reading Charts see ISO 7921 for details, for far vision see ISO 8596). Failure to meet the defined level of acuity, in some cases, may be due to the quality of the test chart produced. Care should be exercised to ensure that the quality of the test chart is appropriate and where personnel fail to meet the required level, the quality of the chart should be reviewed before declaring that an individual has inadequate vision.

If required, the suppliers or manufacturers of the charts may supply a certificate of conformity.

Care shall be exercised when measuring or verifying the eye to chart distances.

Near and far vision testing, or colour vision verification(s) shall be administered by a licensed physician, nurse, ophthalmologist or optometrist; or a person designated and approved by the NDT Level 3.

Test charts shall be in accordance with this International Standard.

Ophthalmologists and Optometrists may use digital charts as an alternative to printed charts.

Prior to the test being carried out, it is necessary to ensure that properly prepared charts of adequate quality are available. Tests shall be administered at a pace and in a manner that puts the candidate at ease. Guidance is given below to allow for proper illumination level of reflective test charts for near, far, and colour vision testing to be measured. Additional information on luminance of luminescent test charts is also supplied for information but it is not necessary to measure at the time of testing.

The chart shall be positioned perpendicular to the line of sight on a flat surface. At no time shall the candidate be permitted to get closer to the chart than the distances below. A ruler or gauge stick may be used to verify the test distance; while traceable calibration is not required, the accuracy of measurement shall be appropriate.

Candidates shall wear the same eyewear, if any, as used during routine NDT inspection. This may be corrective personal protective equipment and/or corrective lenses. Lenses used during an eye examination and not intended for regular use shall not be permitted.

Where corrective lenses are necessary to achieve the required level of vision acuity, this shall be specifically recorded as part of the results of the test.

Only clear ophthalmic lenses or clear contact lenses are allowed during the eye examination, or during active non-destructive testing.

The use of pharmacological agents (e.g. eye drops) that would improve or enhance visual acuity at any distance shall not be used.

General

The tests shall be carried out under the conditions defined below and shall not be limited to a test of an individual eye. Both eyes shall be used together as for normal NDT inspection. Limited or no vision in one eye does not preclude a candidate from taking the test; however, care should be exercised to make sure that any other requirements for binocular vision are accommodated.

Near Vision

Start at a print size that is sufficiently bigger than the limit (about two log-units) and decrease the print sizes until the limit is achieved or exceed. Annex A gives an example of a reading chart (Radner chart). Annex B gives an example of an optotype chart (Snellen chart).

Far Vision

Start at a print size that is sufficiently bigger than the limit (about two log-units) and decrease the print sizes until the limit is achieved or exceed. Annex B gives an example of an optotype chart (Snellen chart). Annex C gives an example of an optotype chart (Landolt chart).

Colour Vision

Start at Ishihara plate number 1 and continue to number 17. Annex D gives an example of an Ishihara chart. Annex E gives an example of a sample Trade Test documentation and sample test.

Near and Far Guidance

The candidate shall identify the characters starting from the left side of line 1 moving to the right until a response is given. This shall be repeated for lines 2 onwards until the candidate reaches the limit of their capability.

Confidence can affect results and candidates shall be encouraged to provide answers even when they express some uncertainty in their ability to identify the characters. The larger characters should be easily identifiable and should be used to relax the candidate and ensure good communication between test administrator and candidate before the limit of acuity is reached. The test administrator should prepare a results sheet in advance or record the candidate’s response in a manner that allows verification of correctness.

If the candidate has a diagnosed condition that creates issues with the use of a reading or Snellen chart a further investigation will be required by an ophthalmologist or optometrist with proper documentation to be supplied to the Certifying Board if required.

Near Vision Reading Chart (example Radner or Snellen) ¹

Annex F gives Corresponding Reading Acuity Notations for Test Distances of 40 cm (16 inches) and 32 cm (12.5 inches).

Far Vision (example Landolt² or Snellen)

Colour Vision (Ishihara)

1. 
   (informative)
   
   Radner Chart (Not to scale)

1. 
   (informative)
   
   Snellen Chart (Not to scale)

1. 
   (informative)
   
   Landolt Chart (Not to scale)

1. 
   (informative)
   
   Ishihara Chart (Not to Scale)

1. 
   (informative)
   
   Sample Colour Trade Test Exam

1. 
   (informative)
   
   Corresponding Reading Acuity Notations for Test Distances of 40 cm (16 inches) and 32 cm (12.5 inches)

1. 
   (informative)
   
   Grey Scale Perception Testing

Grey scale perception testing (not a requirement of this Standard) could be used in addition to the colour test requirements to further test a person’s ability to differentiate between shades of grey for radiography and time of flight diffraction.

— Dr. Koelbl shades of grey test (ONE/TUV/BV) eye examination.

— Skerik grey scale test.

1. 
   (informative)
   
   Low Contrast Visual Acuity

Low contrast visual acuity testing (not a requirement of this Standard) could be used in addition to the colour test requirements to further test a radiographic interpreter.

ASTM E3168-20a details the procedure for determining the low-contrast visual acuity of a radiographic interpreter by evaluating the ability of the individual to detect linear images of varying radiographic noise, contrast, and sharpness.

Bibliography

[1] IS0 7921:2024, Ophthalmic optics and instruments- Near reading charts

[2] ISO 8596:2017, Ophthalmic optics — Visual acuity testing — Standard and clinical optotypes and their presentation

[3] ASTM E3168, Standard practice for Determining Low-Contrast Visual Acuity of Radiographic Interpreters

[4] ISO 10938:2016, Ophthalmic optics — Chart displays for visual acuity measurement — Printed, projected and electronic