Overview
ISO/TR 18476:2017 - Ophthalmic optics and instruments - Free form technology - Spectacle lenses and measurement - is a technical report that documents the workflow from refraction to dispensing with a specific focus on the benefits, manufacturing methods and measurement practices associated with free form technology for spectacle lenses. The report explains terminology and provides guidance on classification, manufacturing processes, measurement and quality control, but does not include proprietary lens-design features supplied by commercial vendors.
Key topics and technical content
- Definition of free form surfacing: description of computer-controlled CNC processes that create continuous, non-symmetrical 3‑D lens surfaces (e.g., single-point diamond turning and soft‑lap polishing) versus conventional spherical/toroidal surfacing.
- Classification of free form lenses: front-surface, dual-surface and back-surface free form configurations (the report concentrates on full back-surface lenses).
- Manufacturing workflows: comparison of conventional surfacing (blocking, generating, fining/smoothing, polishing) with modern free form surfacing steps and implications for production and process control.
- Optical design and benefits: potential advantages such as optimization for individual prescriptions, reduction of oblique astigmatism, customization for as-worn position, frame size and wearer behaviour, and progressive‑power adaptations.
- Measurement and quality control: guidance on surface-shape measurement, through‑power measurement, assessing conformity with standards, measuring the as‑worn position and inspection gates in manufacturing.
- Supporting material: Annex A (typical dispensing flowchart), Annex B (measurement technology), Annex C (glossary of terms).
Practical applications and who uses it
ISO/TR 18476:2017 is intended for professionals across the ophthalmic optics supply chain who need to understand or implement free form technology:
- Lens designers and optical engineers - to align design intent with surfacing and measurement capabilities.
- Laboratory and manufacturing managers - for process selection, surfacing strategy (front/dual/back) and quality-control checkpoints.
- Dispensing opticians and ophthalmic clinicians - to understand as‑worn measurement, customization options and fitting considerations.
- Quality and compliance engineers - for verification methods (surface shape, through power) and inspection gate planning.
- Equipment and metrology providers - to ensure measurement technologies support free form verification needs.
Related standards and resources
- Prepared by ISO/TC 172 (Optics and photonics), Subcommittee SC 7 (Ophthalmic optics and instruments).
- The report contains no normative references but includes a bibliography and normative guidance on measurement and verification practices (see Annex B and C).
Keywords: ISO/TR 18476:2017, free form technology, ophthalmic optics, spectacle lenses, lens measurement, free form surfacing, progressive lenses, as‑worn position, lens manufacturing, quality control.