I opened up an independent optometry practice and haven't sold glasses in 14 years. I want to provide excellent material to compliment my excellent care!
I ordered a PAL lens identifier and didn't receive the unit I anticipated but thought I'd see how well the unit I received performed and it happens to have a polariscope evaluator as well. Trying out the polariscope was illuminating! I've started comparing the amount of distortion, apparent through the birefringence revealed through the the polariscope, of all the lenses that I get back from the different labs I send my frames out to. It varies, I guess, based on many factors but what I wonder is with the manufacturers claiming to reduce unwanted distortion in their PALs via digital surfacing, how much difference can it make if the frames are inducing distortion in the lenses?
I measure base curves and recognize that the frames are capable of inducing measurable warpage of the lenses and I understand that 1D is ANSI standard tolerance. That seems like a lot.
How many opticians use a polariscope or a colmascope when inspecting frame mounted lenses?
cheap 'polarized' WM sunglasses; no distortion
trivex Younger Image PAL; moderate amount of distortion, some in the near reading zone
demo lens w/AR; small amount of distortion inferiorly
hi index flat top; some small amount of distortion around the mountings but pretty clear
SV poly; a moderate amount of distortion in the corners. Looks crisp through the lensometer. There is 0.75D of warpage of the BC. Is the birefringence inferior nasal and superior center a function of frame tension and an indication of distortion or related to being poly?
Perhaps I'm too compulsive. I'm here to learn, so don't hold back.
Reply With Quote
Bookmarks