Overview
EN ISO 9342-1:2023 - "Optics and optical instruments - Test lenses for calibration of focimeters - Part 1" defines reference lenses used to calibrate and verify focimeters that measure spectacle lenses. Published in 2023 and adopted by CEN, this second edition updates the 2005 version and provides requirements, terminology and a method to determine the back vertex power of reference lenses. The standard ensures repeatable, traceable focimeter calibration for quality control and compliance when measuring spectacle form lenses (e.g., lenses evaluated to ISO 8598-1).
Key topics and requirements
- Scope and terminology: Defines terms such as reference lens, back vertex power, verified power, and specific lens types (spherical, prismatic, cylindrical, spherocylindrical, reference filter).
- Design requirements: Reference lenses shall be manufactured from homogeneous white crown glass and be free of bubbles/striae in an 8 mm radius around the centre (see Clause 4.1).
- Types of reference lenses covered:
- Spherical reference lenses (including optional low-power variants)
- Prismatic reference lenses
- Cylindrical reference lens
- Spherocylindrical-power reference lens
- Reference filters (neutral density, including optional darker filters)
- Verified power and uncertainty: A verified power is derived from measured parameters (e.g., refractive index, surface radii, thickness) with associated uncertainty; measurements must be traceable to accredited metrology labs.
- Calibration constraints: Only lenses with integer nominal powers may be used for calibration of digitally-rounding focimeters (Clause 4.1 note).
- Measurement method: The document gives a method to determine back vertex power and includes informative annexes on design and validation (Annex A–C).
- Normative references: Includes ISO 7944 (reference wavelengths) and ISO 13666 (ophthalmic vocabulary).
Applications and users
Who benefits:
- Manufacturers of focimeters and ophthalmic measurement instruments
- Calibration and metrology laboratories providing traceable focimeter verification
- Ophthalmic lens manufacturers and optical labs performing quality control on spectacle lenses
- Regulatory and standards bodies ensuring instrument conformity
Practical uses:
- Routine calibration and verification of focimeters to maintain measurement accuracy
- Validation of automated focimeter readings (dioptric power, prism, cylinder axis)
- Ensuring traceability and reproducibility in eyewear production and inspection
Related standards
- ISO 8598-1 (measurement of spectacle lenses) - typical target for focimeter use
- ISO 7944 - reference wavelengths
- ISO 13666 - ophthalmic optics vocabulary
Keywords: EN ISO 9342-1:2023, focimeter calibration, reference lenses, back vertex power, spectacle lenses, verified power, prismatic reference lens, spherocylindrical reference lens.
