Ophthalmic optics — Spectacle frames — Measuring system and vocabulary
1Key Takeaways
This document specifies a measuring system for spectacle frames and related vocabulary. It is applicable to spectacle frames with fronts that are intended to be symmetrical.
2Expert Interpretation
An in-depth interpretation of the eyeglass frame measurement system and professional terminology in the ISO 8624:2020 international standard, including the principles of the box-type lens system, three-dimensional frame measurement methods, key dimension definitions and technology evolution analysis, providing optometrists and frame manufacturers with a standardized implementation guide.
Interpretation of the core content of the standard
The ISO 8624:2020 standard establishes a measurement system based on the box lens system, and defines three key parameters: horizontal lens size (a), vertical lens size (b), and lens center distance (c). This standard is applicable to symmetrically designed frames, and for the first time systematically handles the measurement of three-dimensional frames with significant face angles.
Key Technology Evolution
| Version | Main Improvements | Impact Dimensions |
|---|---|---|
| 2011 Edition | Basic Measurement System | Two-Dimensional Plane Measurement |
| 2020 Edition | Three-Dimensional Measurement Specifications/Facial Angle Compensation/Nose Pad Asymmetry Processing | Compatibility with Modern Curved Frames |
Case: When the face angle reaches 7°, there is a 0.25mm difference between the 34mm monocular pupil distance measured on the lens shape plane and the measurement result on the front plane of the frame, which directly affects the fitting accuracy of the progressive multifocal lens.
Key Terms Analysis
Box Lens System
The measurement reference of this system is a rectangular frame surrounding the lens shape:
- Horizontal centerline: determined based on the vertex of the frame groove
- Effective diameter: twice the distance from the box center to the farthest point on the lens edge
- Face angle: the angle between the lens shape plane and the frame front plane (Figure 8)
Implementation Suggestions
Measurement Process Optimization
- Preferably use 3D scanning equipment for curved frames
- The reference plane (frame front plane or lens shape plane) must be indicated when measuring lens size
- The measurement of non-articular temples must be kept in a 90° unfolded state (Figure 3)
Special Case Handling
When the nose pads of the frame are asymmetrical (common for custom frames):
The bridge height measurement should be taken from the bridge width line to the highest point on the lower edge of the nose bridge of the frame, regardless of whether the point is on the vertical axis of symmetry (3.2.6 Note 2).