UK Opticians and Add Power

[Darryl Meister]

I've spoken to several US opticians about verifying the add power of progressive lenses, and most seem to use the semi-visible add etchings.

I was curious as to whether European opticians verify the add power using the semi-visible add etchings or actually measure the add power using a focimeter of some sort.

Best regards,
Darryl

[John R]

Depends on wether they know about the markings or not.
I would guess its a 50 - 50 split. Some know of the markings but still send back saying wrong add power.
Trouble with measuring on a focimeter is you need to have the manufactures markings still in place and very few now supply replacement ones that cover the addition checking point.

[Darryl Meister]

Hi John,

Thanks for the feedback. Just to clarify a few of your points:

Depends on wether they know about the markings or not.

Do you mean to say that some opticians are not aware of the semi-visible etchings?

Some know of the markings but still send back saying wrong add power.

Do you mean, then, that some opticians actually measure the add power with a focimeter and decide whether to accept or reject it? If so, if you had to guess, what percentage of opticians actually measure the add power of the lens with a focimeter, versus just inspecting the add engraving on the front?

Trouble with measuring on a focimeter is you need to have the manufactures markings still in place and very few now supply replacement ones that cover the addition checking point.

Do you mean that many European labs remove the ink markings before delivering them to opticians?

Best regards,
Darryl

[John R]

Do you mean to say that some opticians are not aware of the semi-visible etchings?

I would say a few are unaware of them or their staff are.

Do you mean, then, that some opticians actually measure the add power with a focimeter and decide whether to accept or reject it?

Yep i would say most will check on a focimeter, guess they dont always trust manufactures.

Do you mean that many European labs remove the ink markings before delivering them to opticians?

Well its not uncommon for some of the markings to be missing when dispatched. The replacement stickers for UK optical varis do not show where the add should be mesaured at.

[Adam Simmonds]

Sorry to contradict you John, but I'm as amazed at your replies as Darryl is.

I can't speak for every optician (neither can John) but I'd be shocked if opticians or any of my staff were unaware of the add markings on the lenses.

In truth, because it's so tricky reading a varifocal on the focimeter, and because I only ever order Panamic or Gradal Tops, I assume (yes I know about assumptions being the mother of all ****ups!) that the lenses are correct - going by what was ordered and what's on the lens packet.

I always receive lenses with the markings on intact.

P.S. What's the point of the question??

[John R]

Adam Simmonds said:
Sorry to contradict you John, but I'm as amazed at your replies as Darryl is.

Adam, Dont be sorry. I just call them as i see them.
We have had varifocals returned for wrong add powers even though it clearly states on the lens the addition power, and when asked the person has responed with "It reads wrong on the focimeter" and never mention that it is marked up wrong by the manufacture. Which leads on to they dont know about the add markings.

[Darryl Meister]

What's the point of the question??

I'm investigating dispenser habits when it comes to verifying progressive lenses for the development of future dispensing guides, recommendations, products, and so on.

Best regards,
Darryl

[David Wilson]

Darryl,
Without referring specifically to any countries, I suspect that the reason that labs have lenses rejected for wrong add (ie the practitioner measures something different to the marking) is that they have not been checked correctly. Some may measure the back vertex powers of the distance and near rather than the FVP of distance and near. In a script like mine that would create a significant error. The same problem applies to bifocals. Adam, I am sure that this would not be common in the UK, at least with qualified DOs or otometrists, where I know the standards of education are very high.

Incidentally, Mo Jalie has an interesting view on checking front surface bifocals etc, claiming that the textbook method, outlined above, is not the most appropriate way of doing it. I'll see if I can dig out his article.

Regards
David

[Darryl Meister]

Hi David,

I certainly agree that many opticians measure the add power incorrectly. For that matter, it is really not possible to measure the add power of a progressive lens to any high level of accuracy at the dispensing level. There are several optical factors that affect the add measurement, including -- but not limited to -- the type of instrument, the prescription, processing aberrations, and the nature of the design, itself. (And that's assuming that they are using the correct method in the first place.) Consequently, even if a progressive lens was made perfectly by the manufacturer, there is still a chance that the optician will read an error of some sort. And, if the lens has some form of compensated "as-worn" prescription, the process becomes even more confusing.

So, I am curious as to how many opticians actually try to measure these things with a focimeter, versus just reading off the add label/etching.

By the way, are you referring to Jalie's "mechanical" addition?

Best regards,
Darryl

[John R]

Darryl Meister said:
So, I am curious as to how many opticians actually try to measure these things with a focimeter, versus just reading off the add label/etching.

I have always wondered if it has something to do with they have had a error at their end and are looking for a way out. Some go the non-tolerance route but risk getting caught out when re-ordering.
Could also be that they just dont trust anyone but themselves.

[David Wilson]

Hi Darryl,
I agree. I suppose you and your colleagues in the other manufacturers have had many queries about rotating axes etc, found when checking adds on the focimeter. I know that most manufacturers (or their local branches) down our way recommend checking the add by reading the engraving. I agree with this method. I think that it was you, some time back, who made the very good point that the checking circles should be considered as windows of simplicity, provided by the lens designers as a sop to the humble focimeter.

I think that John also makes a good point. Some trust their judgement even when their method may not be correct. Some examples that come to mind are measuring the frame centration distance through not trusting the frame manufacturer, However errors have occurred because the practitioner has measured using datum but used the manufacturer's boxing former. Another is the trust of the PD rule as opposed to the pupillometer. We have discussed this in detail in past posts.

And, yes, I was referring to Jalie's mechanical addition.

Regards
David

[chip anderson]

When in doubt why not mark the centers as you would when measureing for a PAL, check the distance power 3 mm above the mark and then check the add 20 mm down and 2 in from the first mark?

Should work even when the marks are not visible.

Chip