Reading a -27.00 - 2.00 x 175 on a lensometer that only goes to a -20.00
Hey all!
Seeking some feedback here, just curious, how do you all read a lens of this power when the lensometer you're using only goes up to a -20.00? I've heard some differing opinions,so I'm curious what everyone here would do. Would greatly appreciate your
Thanks!
DC
Put a known power lens in front of the lens. Such as a +10 sphere power lens in front of the lens, read it, then add -10.00 sph back into it.
That is like neutalizing by hand in the old days .............should work
Originally Posted by Chris Ryser
I don't totally stop listening when you old fogies start talking wisdom j/k
Cut the -10 lens to fit into the prism adapter, then neutralize as above. Keep it in the box you keep your prisms in and you will never lose it.
If you don't do that, you will get more and more of these jobs until you make one, then you will never get another one, ever.
Great suggestion! I have to do the same thing at least 1 a week when it comes to prism over 5 diopters.
Paul:cheers:
Many trial lens sets have them that will fit nicely.
Diane
Anything worth doing is worth doing well.
If you place it in the auxiliary prism holder, measure the power, and add that back into the new reading.
For example, because the aux prism holder on my Marco 101 is about 60mm from the lens stop, a +6.00 D from my trial lens set reads +9.50, so add -9.50 to your result when measuring a lens placed on the lens stop. This extends the range to -29.50 D. The trial lens isn't centered, so watch for unwanted prism.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
That is definitely the way to go.
Unfortunately I no longer have a marco, I have a Burton 2021 which has no prism holder, instead has a dial-in prism compensation, which is so sensitive it changes its reading if I sneeze, or blink or think too hard (but that isn't relevant here, just a pain in my ***).
So I actually have to put the trial lens on top of the lens in the glasses, or have one of my minions or cohorts do this for me. It isn't perfect, I know but It is fairly accurate and I can double check it with a 12 year old auto lensometer.
Don't scratch the lens!
Fortunately, we don't see >20 D RXs too often- the last one I saw was more than three years ago. WRT precision, keep in mind that mispositioning the lens, wearer's vertex distance-wise, on a 29 D lens by 1mm is more than ±.75 D of error, and that the grinding tolerance is more than ±.50 D.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Hahaha That's true!
Just take for granted that it is correct.
+1+1!!!!!!!!
I just realized that I never came back to comment on this one. My bad! Thanks for all the advice, everyone! New question: How do you accomplish the recommendations above when you have a prism dial on your lensometer, not prism rings (I like the rings so much more!)? Other than just putting a lens in front of the glasses...any other options?
What did you end up dispensing to your patient?
I wasn't dispensing anything...just finding out after the Doc brought a pair of glasses over for one of my opticians to read.
As Diane said a -10.00 trial lens will work well, just compensate for Vertex changes a bit.
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