ISO 10938:2016

Overview

ISO 10938:2016 - Ophthalmic optics - Chart displays for visual acuity measurement - printed, projected and electronic - specifies requirements for high‑contrast optotypes used in clinical visual acuity charts. It applies to optotypes presented on printed media (opaque or transilluminated), optical chart projectors and electronic displays designed for general clinical use. The standard sets performance, measurement and documentation rules that help ensure consistent, reliable visual acuity testing across devices and settings.

Key topics and technical requirements

• Optotypes: Sizes must be specified by a critical dimension (e.g., Landolt ring gap). Comparability with the standard optotype (ISO 8596) is recommended.
• Background luminance: Specified range 80–320 cd/m² (recommended 200 cd/m²). Luminance uniformity limits are defined near the optotype and across the field.
• Contrast: Optotype luminance must be ≤ 15% of the background luminance (accounting for room lighting). Optotypes must have sharply defined edges at specified observation distances.
• Printed charts: Manufacturer must state the designed test distance.
• Projected charts: Resolution requirement expressed as line/mm - minimum is 4× the spatial frequency corresponding to the limb width of the 1.0 decimal optotype. Focus range required: 2.9 m to 6.1 m. Manufacturer must specify suitable projector screens.
• Electronic displays: Pixel size must be small enough that displayed optotypes perform equivalently to those meeting contrast and edge requirements. Notes address greyscaling/anti‑aliasing effects and calibration tolerance (ISO 8596 allows ±5% optotype size variability).
• Range of compliance: Manufacturer must specify the test distances and acuity grades covered (recommended minimum range 0.1–1.25 decimal acuity).
• Conformity & test methods: All tests are type tests. Measuring instruments should have error <10% of the smallest value measured. Resolution testing can use a Ronchi ruling and viewing protocols.
• Documentation & marking: Devices must be supplied with setup/use/maintenance instructions, specification of luminance and acuity ranges, and be permanently marked with manufacturer, model/serial and claim of compliance. Active ophthalmic instruments must also meet ISO 15004‑1.

Applications and users

ISO 10938 is used by:

• Manufacturers of printed acuity charts, chart projectors and electronic acuity systems (design, QA and product specs)
• Clinical equipment procurement and optical clinics (acceptance testing and correct setup)
• Calibration and test laboratories (type testing and conformity verification)
• Regulators and standards bodies assessing device safety and performance

This standard improves measurement consistency, patient safety and interoperability of ophthalmic visual acuity displays.

Related standards

• ISO 8596 - Visual acuity testing: standard optotype and presentation
• ISO 15004‑1 - Fundamental requirements and test methods for ophthalmic instruments
• ISO/TR 19498 - Methods for correlation of optotypes (informative)