Originally Posted by
Robert Martellaro
You said, As a point of example, if PD is determined to be at certain point, then all other calculations will be based off that, especially in a high curve. Get the PD off by 1mm, and now everything is skewed by that.
The best lens designers, at least on paper, have a pretty good handle on how to make a lens that will perform as well as technically possible, assuming that the optician starts with an ideal frame/lens/eye relationship, and is able to supply accurate data for the software to work with. I also believe that the more optimized/compensated lenses are much less tolerant of inaccurate data, compared to spherical best form surfaces and simple PALs. A 3mm position error on a semi-finished lens might be tolerated, but the same error on a highly optimized lens will probably cause symptoms.
You can see some of this for yourself by inputting a large p-value and dioptric power into Darryl Meister's optical analysis program. Observe how the power error and oblique astigmatism reacts to changes in base curves compared to spherical surfaces.
Hope this helps,
Bookmarks