Page 164 - PowerPoint 演示文稿

154 Ophthalmic Lenses

identified, place the lens on the respective brand layout card with two circles
of the lens coinciding with the two circles on the card. Now mark the other
markings.
The following options may be followed:
The microengraving can be detected by reflecting light from the
overhead lights off the lens surface.

Fig. 11.33: Stripped grid
Or, fogging the lens surface by breathing warm moist air onto the lens
surface.
Or, position the light source behind the lens.
Or, hold the progressive addition lens 10-15 cm in front of the striped
grid. Focus on the lens surface.
The marking will stand out against the background as shown in the
Figure 11.34:

Fig. 11.34: Hidden circles relocated

GENERATING PROGRESSIVE POWER SURFACE
A progressive power lens surface is an aspheric surface of the non-
rotationally symmetric type, generated by means of computer numerically
controlled (CNC) machining of either the surface itself or the mould from