ISO 9342-1:2023

Overview

ISO 9342-1:2023 - Optics and optical instruments - Test lenses for calibration of focimeters - Part 1: Reference lenses for focimeters used for measuring spectacle lenses - defines the requirements and verification method for reference lenses used to calibrate and check focimeters that measure spectacle form lenses (for example, those complying with ISO 8598-1). The standard covers design, materials, verified-power determination and marking, and gives guidance for spherical, prismatic, cylindrical and spherocylindrical reference lenses and neutral density reference filters.

Key topics and technical requirements

• Scope and purpose
  • Calibration and verification of focimeters used for spectacle lens measurement.
  • Defines the concept of verified power: a calculated back vertex power derived from measured lens parameters with stated uncertainty.
• Materials and workmanship
  • Reference lenses are normally made of homogeneous white crown glass, free of bubbles/striae within an 8 mm radius of the aperture; other materials allowed if equivalent stability and uncertainty are demonstrated.
• Reference wavelengths
  • Verified powers are reported for a stated reference wavelength: green mercury e-line (λ = 546.07 nm) or yellow helium d-line (λ = 587.56 nm) per ISO 7944.
• Spherical reference lenses
  • Recommended nominal set: −25 D, −20 D, −15 D, −10 D, −5 D, +5 D, +10 D, +15 D, +20 D, +25 D.
  • Aperture ≥ 15 mm; back-surface curvature and centre thickness chosen to mimic spectacle lens form to limit spherical aberration.
  • Example maximum uncertainties on verified spherical power (standard set) range from ±0.01 D to ±0.04 D depending on nominal power (values specified in Table 1 of the standard).
  • Optional low-power set (e.g., ±0.12 / ±0.25 / ±2.5 D) with tighter uncertainty (example ±0.01 D) for validating automated focimeters.
• Prismatic, cylindrical and spherocylindrical lenses
  • Prismatic reference lenses: plane optical surfaces, aperture ≥ 15 mm. Recommended prism powers: 2 Δ, 5 Δ, 10 Δ, 15 Δ, 20 Δ. Uncertainties and validation methods are detailed (see Annex B).
  • Cylindrical and spherocylindrical designs and validation procedures are covered to verify axis and non-symmetric cylinder measurements (Annexes B and C).
• Traceability and marking
  • Parameters used to compute verified power (refractive index, radii, thickness) must be measured using procedures or equipment traceable to accredited metrology laboratories (e.g., ISO/IEC 17025). Recommended protective mounts should be marked with the verified power and reference wavelength.

Applications and who uses this standard

• Calibration and periodic verification of focimeters in:
  • Ophthalmic instrument manufacturers
  • Metrology and calibration laboratories
  • Optical dispensaries and eyewear quality-control facilities
  • Research labs developing lens measurement equipment
• Useful for instrument technicians, calibration service providers and optical engineers responsible for ensuring measurement accuracy of spectacle lens power, prism and axis.

Related standards

• ISO 8598-1 (spectacle lens measurement practices)
• ISO 7944 (reference wavelengths)
• ISO 13666 (ophthalmic optics vocabulary)
• ISO/IEC 17025 (metrology laboratory accreditation)
• ISO/TR 28980 (implications of focimeter design on prismatic values)

Keywords: ISO 9342-1:2023, focimeter calibration, reference lenses, back vertex power, verified power, spectacle lenses, prismatic reference lens, spherical reference lens, calibration standards.