Overview
ISO/TR 11826:2024 - Ophthalmic optics - Spectacle lenses - Aspects of three-dimensional properties and reference markings is a Technical Report from ISO that explains how the three‑dimensional geometry of spectacle lenses and their permanent reference engravings influence lens mounting, measurement and optical performance. It provides background information, terminology, parameters and practical approaches for handling 3D effects, with particular emphasis on back‑surface reference markings created by free‑form manufacturing.
Key topics and technical highlights
- Three‑dimensional lens properties: discussion of how lens thickness, front/back surface geometry and free‑form surfaces affect apparent and actual reference positions.
- Reference markings: treatment of permanent engravings (markings) on front vs back surfaces, and how viewing back‑surface markings through the front surface can be displaced or magnified.
- Optical effects and centration: implications for prism imbalance, optical axis alignment and the “centre of rotation condition” used in dispensing single‑vision and power‑variation lenses.
- Frame geometry impacts: effects of face form (wrap) angle and pantoscopic angle on decentration, fitting height and induced prismatic errors; formulas and illustrative calculations are provided.
- Measurement positions & alignment approaches: options for specifying measurement reference points, including reference coordinate systems tied to engravings and discussion of data communication (e.g., Vision Council DCS).
- Simulation and analysis: results demonstrating how marking images and mounting tolerances can generate positioning errors and how to account for them in practice.
Practical applications and intended users
ISO/TR 11826:2024 is intended as guidance for:
- Spectacle lens manufacturers using free‑form surfacing and permanent back engravings
- Lens edging and mounting equipment designers and measurement‑system developers
- Optical laboratories and dispensers (optometrists, dispensing opticians) who must ensure correct centration and minimise prism errors
- Software and data‑exchange implementers integrating reference coordinate systems and the Vision Council DCS
Practical uses include improving mounting procedures, updating dispensing measurement workflows (to account for wrap and pantoscopic angles), refining digital dispensing systems, and reducing optical aberrations and prism imbalance in finished spectacles.
Related standards
- ISO 13666 - Ophthalmic optics: vocabulary and reference points
- ISO/TR 18476 - Free‑form lens manufacturing considerations (background)
- ISO 8624 - Frame face form / wrap definitions
- Vision Council Data Communication Standard (DCS) - referenced for coordinate/data exchange
ISO/TR 11826:2024 is a useful technical resource for organisations seeking to align manufacturing, measurement and dispensing practices with modern three‑dimensional lens designs and back‑surface marking workflows.