Overview
EN ISO 8596:2018 / ISO 8596:2017 - Ophthalmic optics - Visual acuity testing - Standard and clinical optotypes and their presentation - defines a standardized method for measuring distance visual acuity using the Landolt ring optotype under photopic conditions for purposes such as certification or licensing. It specifies the standard optotype design, visual acuity grades, presentation rules and test-area requirements. The document is explicit that it is not intended as a clinical measurement standard nor for certifying blindness or partial sight; clinical optotypes for research are described informatively in Annex A.
Key topics and technical requirements
- Standard optotype (Landolt ring):
- Grade 1 Landolt ring: outer diameter subtends 5 minutes of arc; ring width and gap subtend 1 minute of arc at the designated viewing distance.
- Eight gap orientations (horizontal, vertical and four diagonals) required.
- Visual acuity grading systems:
- Decimal visual acuity, Snellen fraction and LogMAR are defined and cross-referenced.
- Optotype sizes are graduated logarithmically (series R10, quotient ≈ 1.2589).
- Table of nominal acuity grades (e.g., decimal 1.0 = 6/6) with minimum presentation counts.
- Presentation and layout:
- Minimum spacing between optotypes depends on acuity grade (see Table 2).
- Test field must extend at least 0.5° beyond optotype contours and have a uniformly bright, texture-free background.
- Rotational presentation of optotypes must not reveal orientation cues.
- Test methods and reporting:
- Specifies viewing distances for distance visual acuity testing, criteria for assigning acuity grades, luminance and quality of presentation, and required content of the test report.
- Informative content:
- Annex A lists other clinical optotypes (for research/comparative use) and ISO/TR 19498 is referenced for correlating clinical optotypes to the standard optotype.
Practical applications
- Ensures consistent, reproducible visual acuity testing for certification and licensing (e.g., driver vision standards, occupational health assessments).
- Guides manufacturers of vision test charts, digital acuity displays and ophthalmic equipment to comply with standardized optotype geometry and presentation.
- Supports regulatory bodies and testing laboratories in developing accredited test procedures and devices that adhere to internationally recognized optotype specifications.
Who should use this standard
- Standards and regulatory authorities, certification and licensing bodies
- Ophthalmic equipment and chart manufacturers
- Vision testing laboratories and test developers
- Optical instrument designers and quality managers involved in standardized acuity testing
Related standards
- ISO 3:1973 (Preferred numbers - Series of preferred numbers) - referenced for optotype scaling (R10 series)
- ISO/TR 19498 - method for correlation of clinical optotypes to the standard optotype
Keywords: EN ISO 8596:2018, ISO 8596:2017, Landolt ring, visual acuity testing, ophthalmic optics, optotype, decimal visual acuity, Snellen, LogMAR, photopic conditions.
