Verification of Tolerance: Prismatic Imbalance or PDs and OC Heights
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- čas přidán 18. 08. 2020
- What could be more fun than taking a deep dive into tolerance verification of horizontal and vertical prismatic imbalance? What if we just talk about PDs and OC heights for say 30 minutes?
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Hey All - John Here - There are three videos in this series. Part I and Part 3, this one, seem to get some great views while Part 2 is a little shy but so, so, so important. Please don't miss it: czcams.com/video/EceKSkGIkso/video.html
Thank you! Thank you! Thank you! This drove it home for me. You are a REALLY GREAT teacher.
You are welcome, welcome, welcome. You wouldn't believe me if I told you how hard we tried to find anyone on Earth who actually understands the ANSI standards as written. The video took months, almost a year and it did just about drive me mad... John
Thank you John time 6:04 pm
Nice opener :)
Thanks 😁
What if my PD is 54 but the frames are said to start at 61, would that work ? the bridge is only 14mm. Thanks.
Wow, this video really made things so much clearer for me!!! Thank you thank you! GREAT 3 part series. I'd just like to clarify a doubt in my head I'm still unclear about. When working prentice formula, whether it's a horizontal or vertical imbalance, what do we do if one eye is correct? What if there is no decentration up or down in one eye? We can't do the formula with 0 mm decentration for that one eye can we?
That is why the whole ANSI/ABO Prentices formula stuff is garbage. Just go back to the mantra - if it is wrong sent it back and get it made right. If one lens is perfect and there is enough power for you to pick up an error in the other then figure out where it went wrong (OC no OC, binocular PD when it should be monocular, etc) and send it back. R lens is fine, left lens OC should have been 17 and it is at half the B at 12. Once again you aren't going to waste time trying to figure out if something cancels or compounds! I think you might be "overthinking" it just a tiny bit. You know enough to ask the questions. You know enough to see the problem. Then - You know enough to figure out what went wrong.
Wrong is wrong. If it is made wrong send it back.
Can you go more in depth at 13:35 where you said that regardless of power that as long as the OC is on the same plane for both eyes that it does not really matter? I showed this to my fellow opticians at the office and we are very interested as to why. When we are always taught to take OC for high powers. Any more info on it would be great! :) thank you. Love your content!
Taking OCs for higher powers is a great idea. But - as we know not everyone does it and yet people do just fine with their glasses even in powers that are quite high. Even when we take an OC we don't just jam the lens up 10, 12, 15mm to meet the pupil center since it creates thickness issues. Generally we aim for just a little bump of 5mm or so. I can't remember the exact "thing" behind it but we were taught that the eye and brain are more sensitive to PD error than OC error. Of course vertically (99% of the time) the prism error will be the same BU/BU or BD/BD while in PD error the two will often create the opposite BI/BO or BO/BI since one eye is looking nasally and the other temporally. Which yes creates a cancelling effect but the image shift is opposite eye to eye. Hope that helps - but I'd say the proof is in the pudding so to speak... I'm not anti-OC at all. But what really matters to our brain is that the OCs are on the same plane. John
Laramy-K Optical thank you for the reply. that clears it up for me
What you explain at minute 13:00 and minute 19:00 & 21:27 is what it's important, but yes, you had to explain all the rest around also. Thank you. "If you order 15/15 and you get 14/15, they were made wrong." And absolutely at minute 22:13... XD
Thanks!
I'm still baffled every day by that series.
We challenge the status quo of an entire industry and much of what the accepted certification is based on and we got exactly zero feedback. No discussion. Nothing... I figure it must be either apathy or a lack of understanding. My hunch is a lack of understanding. John
Hello Laramy, I liked good explained...thank you...and please, don't drink and drive...
8:13 R lens with AR and the other without AR :D Correct me if I'm wrong but shouldn't aspherical lenses be centered: far PD R i L separately and OC R and L separately minding the panto (or measuring while perpendicular to the floor)? Event "reading" glasses with asf lenses ought to be ceneted with far PD?
NO, What you never, ever want is for the OC or vertical placement to be anything but equal. Kind of the point of the video. Don't care if they are high, low, spot on as long as they are on the same plane. PDs absolutely monocular but OCs always equal. (progressives can be different).
What is a wave test? My optician did a redo from polycarbonite lenses to 1.67 high index and inside the glasses case were my old lenses that they replaced with a post it on them that said 'wave test'. Just wondering what that could mean.
Sorry but no idea. A lens can have a wave or an area of distortion from surfacing error. Perhaps they have a high end auto lensmeter or a lens mapper that is capable of picking that up. But as to a specific "test" have not heard of that.
@@LaramyKOptical Thanks for the reply. Actually maybe it was the Optician that requested some sort of a wave test when sending them back to the lab and the lab didn’t know what to do with that probably.
Hi John, what are your thoughts about OCs needing to be on the same plane when a patient has one eye that is definitively higher than the other? Should we do different OC heights in that case?
Really tough one there... If you can see the difference just by looking and powers are getting up there it may well be worth experimenting with different OCs assuming that there is a "problem" of some kind you are trying to sort. Might be something to try in basic stock cheap CR-39 as a test and take it from there. John
@@LaramyKOptical We use an Optikam measuring device in our office and it automatically provides OCs for every order, so we usually provide them to the lab. However, we have definitely not been ordering OCs on the same plane - usually it's just a difference of 1 mm or two between the two eyes, but your comments on the importance of them being the same has us concerned. If we do use a digital measuring device like an Optikam should we just split the difference between what it provides as an OC to get just one OC height?
@@kirstenwikingazoulay I've never heard of anyone using different OC heights on routine work. I guess this would be a case of if it works for you keep doing it (?) but it sounds like a horrible idea to me. What would you do if you got a pair like it from outside your office? Wouldn't you think that something was wrong? I mean the very definition of vertical imbalance. The optics of a progressive allow for differing fitting heights but it is not the same for single vision work. I'm surprised your lab hasn't called you out on it? Does the work actually come back with the different OC heights? Always possible I'm missing something... John
@@LaramyKOptical No our lab has never mentioned this to us! I just called them to ask about this, and they said that depending on the office/optician they receive both - orders where the OCs are the same and then split OCs set to different heights for each eye. However, they did say that they generally recommend using identical OC heights where you split the difference between the two eyes (if there is a difference in heights). I am flabbergasted - neither the optician who trained us, any of the 4 labs we work with, instructors from other online courses, etc. have ever mentioned this to us over the year we've been working this job. We'll be switching to doing matching OC heights per your advice. I wouldn't have thought anything of it if I received a pair with different OCs because this was how we were trained.
@@kirstenwikingazoulay Since the very definition of vertical imbalance is that the OCs are not on the same plane I would think that the optician, labs, instructors etc. didn't feel it necessary to even mention it? If they covered verification and/or ANSI stuff it would have been a part of it. Oh well - guess it goes to show that in routine powers it really doesn't matter all that much!
would a OC height matter more if a digitally optimized lens utilizing vertex, wrap, and panto measurements is being ordered? my thinking is yes.
what about when we take half the B for a customer who has been glasses with the OC always in front of their eye? would they be bothered by a pair using half the B? My thinking is it'll be a bit of an adjustment at first but something they will adjust to fairly quickly. It would be a tougher adjustment for higher powers.
OC height will always be one of the point-of-wear (POW) measurements included in a true free-form personalized lens order/design. 99% of the time they will all come from a digital measuring device of some kind.
See: czcams.com/video/el_EAEGSOZE/video.htmlsi=DZ4gDWhJumkT8cEW
As a customer who buys glasses, never ever has any optician come up with any "proof" that the lenses are correctly made if I've asked could there be an issue with the lenses if I didn't see properly or there is something that bothers me in the image produced by the lenses. Maybe I could go and visit another optician and pay them to check if the lenses were made and installed properly in the frame.
Whew - I could go on for an hour here... At the very least any "optician" should be willing to double check powers in the lensmeter and dot up the lenses showing the proper OC/PD placement. Unless they have an auto-lensmeter showing you or proving to you would be a little tricky but certainly not impossible. I've certainly done it. Hopefully you watched the other two videos in that series which might give you more to go on. Now, every lab I know of has an auto-lensmeter and a dual lens mapper and they send that verification slip with each pair they send to the store. That may well end up in the trash but somewhere along the line you have a 70% chance that someone did check them before they left the lab. You probably have a 70% chance that someone checked them when they came into the store but whether that person had any idea what they were doing is another story. Keeping in mind that power(s) aren't the only thing that can create image problems. Anyway - if you came in to the store where I worked and asked me nicely to do a "forensic" exam on your glasses I would have done it for you no charge. I see it as part of being a real optician. Some places may charge a nominal fee for their time. BUT - unless you can also provide a pair that works and any "prescription" information they have nothing to compare their findings to. Hope that helps even a little. John
In vertical prism imbalance
Ordered
OD:-7.00sph , OC:18/18
OD:-7.50sph
Received
OD:-7.00sph , OC: 16/17
OS:-7.50sph
According ANSI.1mm difference (17-16mm)in height of PRPs
Would it pass?
Yes but it has nothing to do with 18/18 and 16/17 only 16/17 being 1 apart. That is basically the example given right? ????
Yes.This is second example.but I add OC
In first example
Power +3.50D OU
Ordered OC 18/18
Received OC 16/15
it would not pass ANSI even 16/15 being 1mm apart?
@@tuoinguyen9061 ANSI is never about the OC given to the OC received. ANSI is about the relative position between the two irregardless of any OC requested. So according to ANSI 16/15 would always pass. YOU (not ANSI) are the one to decide what happens when and if you want to work from 18/18 and work out Prentice's rule and compound and/or cancel. I think you are saying the same thing just in a different way maybe? And - yep it is crazy confusing hence why it took us over 3 months to get it done... If you wanted 18/18 and got back 16/15 send it back and get it made right. Bottom line - who cares what ANSI says!
Thanks
Great stuff so much for doing my own PD and ordering progressives online! Damn you Zenni. Lol
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