Wait, what !?the optometrist does not measure the PD
How would you set up the trial frame without the PD?
How do you setup the phoropter without the PD?
Also most auto-refractometers measure (reasonably well) the PD.
On a different note:
The public obviously do not understand that the PD and the (monocular) horizontal centration distance are two different values.
The later one depends on how the frame sits on the face and varies for each frame.
Well, they put on the trial frame and twist the nobbly bits until the lenses are centred. Simples! We don't use phoropters or auto refractors, so can't comment on them. Some of the big chains do, which is great for independents because so often although the numbers might be correct, they don't take into account real life.Originally Posted by Nikolay Angelov
Wait, what !?
How would you set up the trial frame without the PD?
How do you setup the phoropter without the PD?
Also most auto-refractometers measure (reasonably well) the PD.
On a different note:
The public obviously do not understand that the PD and the (monocular) horizontal centration distance are two different values.
The later one depends on how the frame sits on the face and varies for each frame.
But, Nikolay, exactly how much difference (I'm assuming we're takling tenths of a mm here) do you *rountinely* expect to encounter between PD centered eyewear and *frame* compensated/PD centered eyewear, and...Wait, what !?
How would you set up the trial frame without the PD?
For light to moderate power Rxs, by "eye"...roughly centering the eye
How do you setup the phoropter without the PD?
Same...
Also most auto-refractometers measure (reasonably well) the PD.
Yes!
On a different note:
The public obviously do not understand that the PD and the (monocular) horizontal centration distance are two different values.
The later one depends on how the frame sits on the face and varies for each frame.
how much significant difference in "comfort"/vision would you expect clients would experience/recognize for the same Rx range?
B
Last edited by Barry Santini; 02-20-2012 at 09:41 AM.
When we talk about "PD centered" there are 2 options:difference ... between PD centered eyewear and *frame* compensated/PD centered eyewear
- use total PD divided by 2 to get the mono PD
- use measured mono PDs for both eyes (pupilometer etc.)
We routinely see differences of about 2mm between right/left monocular PD (pupilometer values).
So if we used the PD/2 equation for monocular centration distance (instead of measuring actual mono PD with a pupilometer) we will get a 2 mm total decentration.
If we got the mono PD with a pupilometer (option 2):
However the pupilometer sits on the front of the nose and eyeglasses tend to hold the sides of the nose.
Depending on how irregular the nose is the frame will be shifted differently than the pupilometer was.
What differences could we expect? I have no actual data.
However i will ask my colleagues to measure and attach pupilometer values to the video centration system printouts.
When i get a good amount of data i will share the file and do some simple statistics (mean value, standard deviation etc.).
On small RXs with standard spherical lenses i expect the differences to be negligible (when comparing a pupilometer mono PD and the actual frame horizontal centratrion distance).how much significant difference in "comfort"/vision would you expect
If however we consider a calculated mono PD (total PD divided by 2) i thing the difference would be noticeable (as the error will be larger).
We do a video centration on medium and above RX's and any lens more special than a spherical. All aspheric, atoric, bi/trifocals, PALs and so on pass through video centration (mandatory).
The only reason we don't do moderate RXs with spherical lenses is because of time constrains (they get a conventional pupilometer measurement).
PS: The phoropter takes automatically the PD from the auto-refractor/keratometer (in our case).
PD could be fine-tuned in the "PD mode" where crosshair lenses are inserted and the eyes illuminated.
Last edited by Nikolay Angelov; 02-20-2012 at 11:33 AM.
I completely agree here.
I do however feel, as many on here do, that online is here to stay unfortunately. We have to adapt and find a way to operate with it. I have set up a fee for measuring their PD, advising that they need an OC or Seg for accuracy that we cannot do without the frame, and asking that they return with the glasses to verify that my measurements were fabricated correctly. I've only had to do this twice in the last year and a half.
I find it interesting, and somewhat irritating though, when the patient comes to you asking for help to order their glasses online though. I tell them my policy above and send them on their way.
What "visual health" is endangered if the PD is off, or the Rx for that matter (some strabismus patient's excepted)? If the glasses are wrong the patient just doesn't see until it's fixed. He doesn't develop an eye murmer, or go blind, or lose vision.
Now if you dispense the wrong drops for glaucoma or hypertension, or something you are endangering his "visual health."
Lets not over-rate the importance of a pair of glasses.
Chip
And no, I am not in favor of mail order glasses. I also don't think the patient should be locked into the prescribers shop either.
With a very complex (eg digitally surfaced progressive) or specialist lens a very accurate PD and proper vertical fitting can make a big difference for the customer.
However, for the basic single vision specs (which is the primary market for most online outfits) its really not rocket science and we should stop pretending it is.
Most frames move around on the face far more than the mm or so some are fussing about.
Also, let's not forget that with advances in smartphones it's only a matter of time until most online shops convert to a digital image based system that isn't all that different from what many brick-n-mortar shops do today anyway. Many online shops already send out the frames free for in-home fittings before purchase so they just need to have the customer use an app to take some pics with the frame on. The PD (mono or otherwise) and seg height or other measurements can be taken remotely.
With the right technology and records on the lens placed in the frame the same techniques could be used to verify final fit and alignment remotely as well to ensure then final lens lines up correctly on the face.
If the customer doesn't recognize the value of the service offered by a B&M shop then that's the problem... not some nonsense over PDs.
Does the Porche dealership lose some customers because they'd rather just buy a Chevy? Yes.
Are there measurable differences that make the Porche a better car? On some factors, yes. Do all customers care about those factors? No.
Would a dealership that sells Chevy's at Porche prices do well? Heck no.
Those of us in the traditional non-chain B&M optical business are the Porche dealerships of the optical industry. ...however if customers perceive that we only provide Chevy's at Porche prices don't be surprised if they go elsewhere.
Well said for both opt63 and Chip. I really like the Porsche analogy opt63. Right on the money there.
This is the truest thing ever said on the forum.
B
I provide Volkswagons. Or as I like to say, Porsche-lite.
Yeah Santini its a Porsche 914 but it was a VW/Porsche design.
By the way the 911 turbo 6 fits very nicely in the back of this one too.
- Optician
- Frame Maker/Designer
- Teacher of the art of crafting handmade eyewear.
That's what I get for quickly responding too quickly.
I don't think so either Chip, it is HORRIBLE. Just last week, they found a patient who had been locked in the exam room for over two weeks until he finally succumbed, but only after ancient Chinese tortures were applied.
makes sense. Who ever builds the eyewear, should be responsible for all of its proper measurements, eye size, temple length, pd.......
Seems to me that a while back there was a court ruling that the last person to touch or modify a contact lens was liable.
Hense many practioners stopped doing (to the detriment of the patient) any modification in house. This leaving the lab responsible for adverse effect. Pehaps there is some sort of similar thing where we can make the person who makes the glasses responsible, and of course we will have to keep our hands off for adjustments.
Chip
Chip, I'm usually the first to agree with your visual health point. But...having just completed an article on 3D and eye-synching/eye-teaming, I'd have to say that there *are* insidious associated effects with glasses whose centering, prism, or lack thereof may impact eye-syncing in a latent manne, not overwise normally obvious. Especially with children, these effects can significantly impair their reading speed, comprehension and retention. Adults may actually be suffering from similar effects, but just shirk it off to being tired or disinterested in the subject matter.
Lot's to learn about here. I'm thinking that I will modify my current stance about the visual effects of mismade eyewear.
drk should luv this one...
B
Gentlemen, may I be so bold as to state the obvious. No dispenser in their right mind is happy to have online opticals biting at their balance sheets. But they are. You guys crack me up by arguing the ethics, morality and liability of releasing a PD. In a prior post Barry Santini stated something to the effect that eye wear is viewed by consumers as a commodity and I believe he is correct. When dealing with a commodity 99/100 price wins. So suck it up and give the people something extra in the way of customer service or whatever to make them feel that spending a couple of bucks more with a local business is actually in their best interests. Hopefully that puts the commodity aspect in the back seat. But if you have to bust out a deal to keep that price conscious patients in house I say do it. After years of being aggravated with 1800 Contact you know how I ended up dealing with them ? I straight up match their price. Do I make a big profit, no. Do I retain my patients and keep money out of their tills...yes. Anything that weakens an enemy ultimately strengthens your position. And make no mistake about it, online retailers, across the board, are at war with brick and mortar businesses. It's a combination of practitioner greed and consumer savy that fuels the on line beast. If a patients is asking for their PD instead of getting upset...try asking yourself what happened to make this patient wander off the path to your door.
Last edited by RIMLESS; 02-22-2012 at 06:43 PM.
90% of everything is crap...except for crap, because crap is 100% crap
As analogies go, yours is singularly uncompelling.
Corrective lens prescriptions are written so that a given patient can have lenses made for a given purpose. If that isn't patently obvious, then why else would a refraction include testing at different distances? And why else would phoroptors adjust to bring the lenses over the center of each pupil? And if PD is irrelevant to an Rx then why, after having made the aforementioned adjustment, does the PD (or a close approximation thereof) automatically appear on the PD SCALE on the phoropter? The point is, a refraction cannot even be done if the each lens of the phoropter isn't centered over each eye such that the distance between the centers of the lenses closely matches the patient's PD!
Without a PD, lenses cannot even be manufactured, let alone used for a given purpose. Without an accurate PD, corrective lenses do not correct. That being the case, PD is an integral and essential component of an Rx.
What is an Rx without a PD? INCOMPLETE !
Instead of quibbling over the extra 2 minutes spent measuring PD, why not charge whatever it costs to those who don't like, or can't afford, any of the frames you carry? Or just hang a sign on your window that says "No Framy – No Prescripty".
The PD is taken by the optician who will verify it.
No one is saying a PD isn't necessary to make a pair of glasses, nice strawman. The pd is not measured by the doctor, it is measured by the optician. You pay for the doctor's exam, if you go elsewhere to purchase glasses you didn't pay for my services.
Let me ask you a question, if we should measure everyone's PD for free should we also measure their seg height for an online progressive lens purchase too? Because you cannot have a pair of progressive lenses without a seg height, it would be as you said, INCOMPLETE! (In this example the customer got 3 trials frames from an online store and brought them into the doctor's appointment so they could have us measure the seg)
How we deal with it:
We are happy to give people their PD if they have purchased glasses with us in the past. We are also happy to give them their mono pd from the auto-refractor if we still have that on file and they haven't purchased glasses with us before. If someone wants a more accurate measurement we do charge to take their PD and we offer free troubleshooting and adjustments for the lifetime of their glasses.
Last edited by NAICITPO; 11-20-2023 at 08:02 PM.
You really don't know that much. I'm going to take you apart. Watch.
Sometimes. If so, they're specified as such. Example SVDO, SVNO, over-CLs, computer use, etc. Other times it's a general prescription for an optician to design glasses with.Corrective lens prescriptions are written so that a given patient can have lenses made for a given purpose.
Almost all refracting is at infinity. Only exceptions around here are for emerging presbyopes.If that isn't patently obvious, then why else would a refraction include testing at different distances?
Monocular refractions don't require any specific attention to centration. All refractions on absolute presbyopes are done monocularly.And why else would phoroptors adjust to bring the lenses over the center of each pupil?
Otherwise, it is good to have the patient look through zero prism when doing binocular refractions or measuring ocular deviations.
Nobody measures a p.d. that way. It's totally imprecise. It works the other way around: if you want zero prism, you use the scale to separate the lenses to the proper distance.And if PD is irrelevant to an Rx then why, after having made the aforementioned adjustment, does the PD (or a close approximation thereof) automatically appear on the PD SCALE on the phoropter?
I can refract with a loose trial lens.The point is, a refraction cannot even be done if the each lens of the phoropter isn't centered over each eye such that the distance between the centers of the lenses closely matches the patient's PD!
This you have right. Whomever designs the lens should have a p.d. Among other biometric data. You can also apply your thought process to those other data, and quit making p.d. some special issue.Without a PD, lenses cannot even be manufactured, let alone used for a given purpose. Without an accurate PD, corrective lenses do not correct. That being the case, PD is an integral and essential component of an Rx.
What is an Rx without a PD? INCOMPLETE !
What is the Rx without an optician? INCOMPLETE
Last edited by drk; 11-21-2023 at 12:25 PM.
jasg- Just what is your title in our field? Other???
You're resurrecting 10 year old threads and it feels like you are trolling.
@JASG here are some other older threads that I am awaiting your amazing insights on.
https://www.optiboard.com/forums/sho...-ON-DISPENSING
https://www.optiboard.com/forums/sho...p/59620-Trivex
https://www.optiboard.com/forums/sho...e-a-confession
https://www.optiboard.com/forums/sho...Prism-thinning
https://www.optiboard.com/forums/sho...Med-versus-VSP
Ya’ll do realize that in the UK, where this petition started, optometrists are called opticians, right?
That said, this is a problem (& a petition) for doctors, not U.S. opticians……..
You know Barry, you made a wise statement in 2000 when you said this! Some still argue about a simple PD! We as a profession/trade/job......need to do a lot of things. I'm working now to do just that! Look for it down the road! Professions have much in common. Common education and training, licenses to practice in some cases, or like CPAs, advanced Certification, called CPA! We are working towards something like that!
"This is why I've said we as a profession must reflect upon exactly what we say is the real danger with online eyewear. Trying to falsely tap into the public's emotions with unsubstantiated scare tactics will not work. It will in fact, work against us."
I hope you have a wonderful holiday season, Bubba Santini!
They are referred to as Ophthalmic Opticians and require a formal education. We attempted to do the same thing here in starting the Society to Advance Opticianry. We wanted to recognize those who saw value in education and training. They made a membership organization out of it.
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