Basic spectacle frame parameters – axis system
Introduction
Spectacle frame has some important parameters which are important for spectacle lens centration. Mainly it is spectacle frame size which contains bridge size and eye frame size. Next important parameter is eye frame height which is important mainly for bifocal and progressive lenses. There are two types of frame measurement system – axis system and boxing system. In this exercise we will work with axis system.
Goals
- Draw the frame schematically
- Draw horizontal and vertical axis of the frame
- Do the measurement of basic spectacle parameters and mark them in the scheme
Equipment
Spectacle frame, rule or millimeter rule, writing equipment, calculator, mirror.
Methods
Draw the frame schematically
Draw the spectacle frame with the front side put on the paper. Draw the inner shape of both eye frames.
Draw horizontal and vertical axis of the frame
Height of the eye frames divide in two half and middle point use for construction of the horizontal axis. Width of the eye frames divide in to half too and construct vertical axis.
Do the measurement of basic spectacle parameters and mark them in the scheme
Measure particular parameters of the spectacle frame. Measurement is related to horizontal axis not to boxes of the eye frames.
Results
Draw the frame schematically
Draw horizontal and vertical axis of the frame
Do the measurement of basic spectacle parameters and mark them in the scheme
OR =
d =
a =
b =
Discussion
All measured parameters related to horizontal axes. It means that there is difference in some spectacle parameters. Eye frame height should be the same for both systems. Exact measurement of the spectacle parameters is important for grinding the lenses. Currently these parameters are measured automatically with special readers (tracers) which send measured parameters right into the grinding machine.
Conclusion, notes, comments
Which spectacle parameters are written on the spectacle side or spectacle bridge?
Which are average values for eye frame width and bridge size for standard spectacles?