Overview
ISO/TS 6838:2024 addresses proposed tolerances and measurement methods for multifocal contact lens addition power. The Technical Specification focuses on refractive/symmetric multifocal designs and sets out proposals for measuring the base and add power of these lenses. It explicitly excludes diffractive multifocal lenses and the measurement of distance (label) power. The document is intended to solicit feedback from clinicians, manufacturers and health authorities and is not intended for use as a production acceptance or quality control standard.
Key Topics
- Scope and purpose: Proposals for tolerances and test methods specifically for multifocal add power rather than distance power.
- Tolerances: Framework for tolerance limits and conditioning of lenses prior to testing; separate considerations for rigid and soft materials are discussed.
- Measurement methods: Detailed methods described include:
- Wavefront sensor (WFS): Instrument specification, calibration, in-air and immersed measurement considerations, and example power profiles.
- Focimeter: Principle, specification, calibration and procedures to measure most-plus and least-plus power points.
- Ring test results: Results and analysis from interlaboratory ring tests, including calibration verification and gauge repeatability and reproducibility (GR&R).
- Discussion and challenges: Practical measurement challenges (e.g., immersed vs in-air WFS), calibration lens accuracy requirements, and questions to resolve before potential standardization.
Applications
This Technical Specification has practical value for a range of stakeholders involved in contact lens design, testing and regulation:
- Clinicians and researchers: Understand proposed measurement approaches and their limitations when evaluating multifocal addition power in study settings.
- Manufacturers and test labs: Review proposed tolerances, calibration needs and equipment specifications (wavefront sensors and focimeters) to inform internal test methods and R&D.
- Health authorities and standards bodies: Use the document as a consultation tool to assess measurement consistency and identify open questions before formal standard adoption.
Although informative, ISO/TS 6838:2024 is not intended to be used as a binding acceptance criterion in quality systems - its primary role is to gather feedback and harmonize measurement approaches.
Related Standards
- ISO 18369 series (contact lens standards) - note ISO/TS 6838:2024 clarifies add-power measurement where ISO 18369-3:2017 does not specify methods for multifocal add power.
- ISO/TC 172/SC 7 working documents and guidance referenced in the TS for optics and ophthalmic instrumentation.
For implementation, stakeholders should review the full ISO/TS text, consult calibration-lens requirements described in the ring-test summaries, and participate in the feedback process to refine these proposals.