Did you know this secrets:

[OCP]

Everyone are talking about individualised lenses, vertex distance, Pantoscopic tilt etc, etc, but did you know that:

• The Vertex distance have none (or lets say less) influence on the optical experience.
• The Pantoscopic tilt the same.
• The most important measure is the frame curve

Vertex: Vertex distance is ONLY usefull if you measure the distance behind the eye examination equipment first, and then compare it with the vertex distance you measure with the new frame. It´s the difference that counts. At the same time the vertex distance is close to impossible to measure 100 % correct, and will only make a little power changing if the power is above 5 D.(if you manage to measure both measures correct)!!! Therefore this measure is not used at all from any manufacturer. A secret ? YES DEFINITE !

Pantoscopic: Close to be the same issue as above. You can measure 100 % correct angle, but only in the angle that the client want to stay in that day, so no manufacturer use this either, because no person stay with the same head angle all day..

Frame curve: This is important. Lets say VERY IMPORTANT. This measure will radically change the power when the frame is curved. But did you know that this actually is the only measure you need to take to make a perfect power compensated lens.? I guess not, because if you ask the industry they will claim you need to measure all three measures to make it individual. They only say this because the other does. Thats a fact.!

No matter what your supplier claims, this two measurements, Vertex and Pantoscopic, will only change power theoretical, and give not any optical improvements in real life. For the manufacturer this is a question of making the most individual and personalised lens out there, but lets get our feet on ground again. With all these measures we are only getting confused and we all think we do it so damn great by measure all these data. And for NO reason. THATS THE TRUTH.!
Have a nice Christmas everyone, and sorry for my school english.:finger:

Mike (Shamir wholesaler)

[AWTECH]

• The Vertex distance have none (or lets say less) influence on the power.
• The Pantoscopic tilt the same.
• The most important measure is the frame curve

Vertex: Vertex distance is ONLY usefull if you measure the distance behind the eye examination equipment first, and then compare it with the vertex distance you measure with the new frame. It´s the difference you can use. At the same time this measure is close to impossible to measure 100 % correct, and will only make a little power changing if the power is above 5 D.!!! Therefore this measure is not used at all from any manufacturer. A secret ? YES DEFINITE !

Pantoscopic: Close to be the same issue as above. You can measure 100 % correct but only with the angle the client stay in that day, so no manufacturer use this either.

Frame curve: This is very important. Lets say VERY IMPORTANT. This measure will radically change the power when the frame is curved. But did you know that this actually is the only measure you need to take to make a perfect power compensated lens.? I guess not, because if you ask the industry they will claim you need to measure all three measures to make it individual. They only say this because the other does. Thats a fact.!

No matter what your supplier claims, this two measurements, Vertex and Pantoscopic, will only change power theoretical, and give not any optical improvements in real life. For the manufacturer this is a question of making the most individual and personalised lens out there, but lets get down on earth again. With all these measures we are only getting confused and we all think we do it so damn great by measure all these data. And for NO reason. THATS THE TRUTH.!
Have a nice Christmas everyone, and sorry for my school english.:finger:

Mike (Shamir wholesaler)

This is a very accurate statement regarding position of wear.

I would just like to add that the individualization of the height of the add relative to the distance optical center can vary for each frame by any amount the software designer chooses, but the patient who has been wearing a progressive lens is going to have his eye and brain expect the add to come into full power at about the same distance as before. So if the patient has been wearing a frame with 26mm B and a fitting height of 18mm. The optical center of the standard PAL would be about 2 mm above the bottom of the B measurement. Now if they select a sunlens that is an aviator shape with a B measurement of 38mm and the fitting height is now 30mm for example. Some lens design may optimize this to extend the corridor and the optical reading center to be their longest. This may increase the corridor length from 13mm to 17mm or 4mm more eye movement required when they switch from one to the other.

There is alot that can be done to individualize but what is practical, and what can properly explained so true improvements are delivered.

Some of these new possiblities have greater risks than rewards.

Example: Online ordering by the optician takes out one great previous remake reason. The person calling in the job or the person writing it down at the lab made a simple error. Each time you eleminate the possiblity for an error the better. Is the gain with some of this individualization really worth it?

[THE MEB]

I agree wholeheartedly with the comments regarding vertex distance, and pantoscopic tilt, especially for myopes, have no large effect in the patient seeing better. I have been fitting glasses for 35 years, and it's been my experience, practically speaking, that the major improvement that can be made to help the patient see better is changing the frontal bow of the frame to accomadate their rx.
With myopes, I have found that the flatter the frontal bow, the more clearly the patient sees. Conversly, with hyperopes, the more frontal bow given the more clearly they see. Also, it seems, that typically hyperopes prefer more pantoscopic tilt than myopes.
Of course these finding are just generalizations, but it has been my experience that the more myopic or hyperopic a patient is, the better the results of changing the curve of the front of the frame becomes. I have also seen the opposite of what I described holds true as well, but very rarely.
The point being, the first thing I try to do, if the patient is not seeing clearly out of their new rx, and you have already checked to see if rx and seg heights etc.. are lined up properly, is to alter the frontal bow of the frame. I have found this to be a huge help through the years.

[cocoisland58]

The point being, the first thing I try to do, if the patient is not seeing clearly out of their new rx, and you have already checked to see if rx and seg heights etc.. are lined up properly, is to alter the frontal bow of the frame. I have found this to be a huge help through the years.

True and in fact a little bit of everything might help but the frontal curve makes the most difference. Always check against their old frame. You know how often someone is wearing an extreme flat or an extreme curve on their old frame simply because of them being bent over the years and they have adapted.

[OCP]

Example: Online ordering by the optician takes out one great previous remake reason. The person calling in the job or the person writing it down at the lab made a simple error. Each time you eleminate the possiblity for an error the better. Is the gain with some of this individualization really worth it?

This is very true. The suppliers want us to take all these measures, and everytime they ask you to take a new measure, you will only increase the risk of errors.
In my opinion (as Shamir wholesaler) we recommend our customer when they order Auto II, only to measure the Faceform angle (the curve of the frame) with the Panorameter, Vertex in 13 mm (just to write something and to let the software accept the order) and for the Pantoscopic tilt choose 9 if the frame looks normal to the cheek, 12 if it´s very obliqe angle, and 5 if its a very vertical angle to the cheek. We don´t recommend to measure the Pantoscopic tilt with the Panorameter or others, but only visuel consider which angle to order. It´s impossible to measure the Pantoscopic tilt correct with any equipment. Only the front curve of the frame is a stationary measure that will not change.

Mike

[AWTECH]

This is very true. The suppliers want us to take all these measures, and everytime they ask you to take a new measure, you will only increase the risk of errors.
In my opinion (as Shamir wholesaler) we recommend our customer when they order Auto II, only to measure the Faceform angle (the curve of the frame) with the Panorameter, Vertex in 13 mm (just to write something and to let the software accept the order) and for the Pantoscopic tilt choose 9 if the frame looks normal to the cheek, 12 if it´s very obliqe angle, and 5 if its a very vertical angle to the cheek. We don´t recommend to measure the Pantoscopic tilt with the Panorameter or others, but only visuel consider which angle to order. It´s impossible to measure the Pantoscopic tilt correct with any equipment. Only the front curve of the frame is a stationary measure that will not change.

Mike

You have developed an excellent yet simple method for Panto and if they are off by 2 degrees the compensation will be insignificantly changed. We use 13.5 mm vertex as our default. (and 0.5mm will have almost no change to the prescription or the number).

The big advantage to a device for patient measurement will be to show the patient how high tech and individualized the measurements are compared to how they have always been previously fitted.

[YrahG]

Panto and Faceform have the very same effect on the prescription. In a PAL since we have a narrow corridor the design of the lens can benefit from the faceform measurements becuase the same degree of panto is only going to move the reading area higher or lower where as the faceform will narrow the corridor. This thread is the exact reason why the need to know if the effect panto and face is taken into consideration into both the prescription and the design.

The very same thing can be said about FF lenses compared to conventional lenses. If we are to pursuit precision we shoudn't set caps or ceilings on ourselves.

I remember when opticians used to teach each othr to fit certain lenses 1mm lower or 1mm higher instead of avoiding the design if it did not work for that patient.

[AWTECH]

YrahG said:

The very same thing can be said about FF lenses compared to conventional lenses. If we are to pursuit precision we shoudn't set caps or ceilings on ourselves.

We also have to be careful to not setup measuring and other detailed specifications that can not be followed by the majority of opticians, or we need to have an industry standard. Or each company would have their own method to determine which opticians were approved to take measurements that the majority of opticians were likely not be able to obtain correctly.

As an example of the difficulty in requiring measurements that are not the daily standard, we still have a problem getting the majority of optician, many of whom are very good and skilled into sending an optical center height for a single vision lens. (They expect you to split the B measurement, which works great for a round Ben Franklin style of frame but not very well for a fashion wrap)

[Barry Santini]

Everyone are talking about individualised lenses, vertex distance, Pantoscopic tilt etc, etc, but did you know that:

• The Vertex distance have none (or lets say less) influence on the optical experience.
• The Pantoscopic tilt the same.
• The most important measure is the frame curve

Vertex: Vertex distance is ONLY usefull if you measure the distance behind the eye examination equipment first, and then compare it with the vertex distance you measure with the new frame. It´s the difference that counts. At the same time the vertex distance is close to impossible to measure 100 % correct, and will only make a little power changing if the power is above 5 D.(if you manage to measure both measures correct)!!! Therefore this measure is not used at all from any manufacturer. A secret ? YES DEFINITE !

Pantoscopic: Close to be the same issue as above. You can measure 100 % correct angle, but only in the angle that the client want to stay in that day, so no manufacturer use this either, because no person stay with the same head angle all day..

Frame curve: This is important. Lets say VERY IMPORTANT. This measure will radically change the power when the frame is curved. But did you know that this actually is the only measure you need to take to make a perfect power compensated lens.? I guess not, because if you ask the industry they will claim you need to measure all three measures to make it individual. They only say this because the other does. Thats a fact.!

No matter what your supplier claims, this two measurements, Vertex and Pantoscopic, will only change power theoretical, and give not any optical improvements in real life. For the manufacturer this is a question of making the most individual and personalised lens out there, but lets get our feet on ground again. With all these measures we are only getting confused and we all think we do it so damn great by measure all these data. And for NO reason. THATS THE TRUTH.!
Have a nice Christmas everyone, and sorry for my school english.:finger:

Mike (Shamir wholesaler)

I'm not sure I completely agree with all the above.

IMHO, Panto really comes into its own in a progressive lens, where it helps define the visual axis obliquity in the near zone.

Some whole lens optimization programs, I believe, help correct/reduce unwanted astigmatism in the near zone with large deviations in panto value from the norm range, and also employ VD to further iterate the result.

And, if frame curve was realy so important, as you say (and I'm not saying it isn't, but since your kinda speaking from Shamir's viewpoint), then why does Auto II SV POW FF range allow up to 15 degrees of FF, with no POW compensation for the same in evidence?

To the best of my knowledge...and I certainly could stand to be corrected here....

B

[YrahG]

YrahG said:

We also have to be careful to not setup measuring and other detailed specifications that can not be followed by the majority of opticians, or we need to have an industry standard. Or each company would have their own method to determine which opticians were approved to take measurements that the majority of opticians were likely not be able to obtain correctly.

As an example of the difficulty in requiring measurements that are not the daily standard, we still have a problem getting the majority of optician, many of whom are very good and skilled into sending an optical center height for a single vision lens. (They expect you to split the B measurement, which works great for a round Ben Franklin style of frame but not very well for a fashion wrap)

I agree it'snot for the faint of heart, but I would ventue to say that the number of opticians sending in this data now is very small. Even I myself will leave these figures out in low powers.

A traditional lens assumes a panto of roughly 10 to 15 degrees and a face of 5 to 8 degrees. There exists a rule of thumb where we should lower the OC 1mm fro every 2 degrees of panto and this would allow us to not compensate the prescription. It used to be that a properly fit frame would have roughly 5 to 8 degrees of faceform and decentration of 2 to 3mm per eye. That wrap and that decentration go hand in hand. The need for compensations exists because opticians don't follow good fitting procedures anymore, frame manufacturers make frames that cannot have panto adjusted, and many other factors. As worn has become a method of correcting mistakes our industry has created and the measure of the variables to provide precision eyewear will be a tool best used by the brighter opticians, but I wouldn't call it unnecessary.

[AWTECH]

If you read all of the opinions in various post by many different optical professionals, you will see there are many different opinions.

I believe at some point you have to accept the manufacturers required information and procedures and follow them, if you don't get the patient satisfaction you are expecting it will probably be better to just find another supplier who you can work with.

If you can't trust the lens design specifications, rules, and recommendations, I don't think trying to add individualized tweeks to the supplied data will deliver a better lens for the patient. In fact these tweeks are likely to cause problems as only one suspected aspect has been addressed and this information is all related to all of the other required information. The possiblity for errors is increased due to the significance of the order of the various math formulas usage and the resulting compensation can be changed by using any substitute provided data that is not recommended by the supplier.

Another source for potential error is the lab management system and the interface with the lens calculation software. Unless the correct exchange of this information happens there is real possiblity that one lab management system might produce a lens design slightly differently than another. This is a great challenge for the lens companies as they try to distribute lens design software to work with different software and hardware platforms.

[YrahG]

If you read all of the opinions in various post by many different optical professionals, you will see there are many different opinions.

To each there own, this is a great place to share the things we learn and tweak our opinions to create a uniform truth.

I believe at some point you have to accept the manufacturers required information and procedures and follow them, if you don't get the patient satisfaction you are expecting it will probably be better to just find another supplier who you can work with.

Great and wise statement, a one size fits all philosophy never worked for me. I like to have a few progressive designs in my arsenal.

If you can't trust the lens design specifications, rules, and recommendations, I don't think trying to add individualized tweeks to the supplied data will deliver a better lens for the patient. In fact these tweeks are likely to cause problems as only one suspected aspect has been addressed and this information is all related to all of the other required information. The possiblity for errors is increased due to the significance of the order of the various math formulas usage and the resulting compensation can be changed by using any substitute provided data that is not recommended by the supplier.

This is the truth, everytime the optician or fitter uses a tweak the design has been comprimised. Better to move on, too many good designs out there to try the one size fits all method.

Another source for potential error is the lab management system and the interface with the lens calculation software. Unless the correct exchange of this information happens there is real possiblity that one lab management system might produce a lens design slightly differently than another. This is a great challenge for the lens companies as they try to distribute lens design software to work with different software and hardware platforms.

Communications standards exist, now how each manufacturer implements them and which proprietary procedures they implement are a different story. That's where things will differ by lab, some will invest int he top of the line to ensure great products are produced consistently, others will go for the cheap equipment just to use the FF buzzword. This is the foundation of a good FF offering through any ECP's office determining who is willing to invest in this technology and who's just exploiting it. I use a lab that invests in this technology, I have seen their equipment first hand and know it is some of the best, I have also seen their commitment to perfection in the QC department, this is where I am the most interested. Once again I know that the design is not the labs it belongs to the manufacturer, the QC is the key to ensureing that my trust in the manufacturers design was delivered by my lab.

[Darryl Meister]

Pantoscopic tilt etc, etc, but did you know that:

• The Vertex distance have none (or lets say less) influence on the optical experience.
• The Pantoscopic tilt the same.
• The most important measure is the frame curve

Unfortunately, I think you have been misinformed. Several of the points made in this post are not entirely accurate. To assert that the company you are affiliated with, Shamir, only utilizes position of wear measurements for prescription compensation is one thing. I completely agree that prescription compensation offers only minimal visual benefit to the wearer, as I have described ad nauseam in other threads, including this post from just a few days ago.

But the assertion that position of wear measurements do not influence optical performance, or that other lens manufacturers do not utilize these measurements when designing and fabricating free-form lenses, is incorrect. The position of wear can significantly influence optical performance over the entire lens design in many cases.

Basic prescription compensation, on the other hand, only improves vision through a narrow region of the distance zone. Further, any eye care professional can apply this form of prescription compensation to any lens, even semi-finished, using free software tools.

I have included an actual optical comparison of three different lenses, which demonstrates the influence of the position of wear. I would also encourage you to review US Patent 6,089,713, which details the use of position of wear measurements when calculating free-form lens designs.

Vertex distance is ONLY usefull if you measure the distance behind the eye examination equipment first, and then compare it with the vertex distance you measure with the new frame. It´s the difference that counts

This, again, refers to the same type of prescription compensation that eye care professionals have been applying for years. Free-form lens designs that are truly customized for the position of wear, on the other hand, utilize the vertex, or stop, distance to perform optical ray tracing of a lens-eye model in the position of wear. This is completely independent of any vertex compensation applied because of differences between the refracted and fitted vertex distances.

Frame Curve... This measure will radically change the power when the frame is curved

Actually, for a given base curve, the curvature of the frame can only influence optical performance by changing the position of wear, since decentering a meniscus lens introduces lens tilt. Otherwise, the curvature of the frame has no more effect upon optical performance than the color of the frame.

Now, if you have chosen to substitute a steeper or flatter base curve in lieu of the manufacturer's recommended base curve to achieve a better fit in a frame, thereby violating "best form" optical principles, sufficiently advanced free-form lens designs with full optical optimization can apply the necessary optical corrections over the lens surface.

If you read all of the opinions in various post by many different optical professionals, you will see there are many different opinions.

But, sadly, the opinions often expressed on the Internet do not represent facts. Nevertheless, it would be nice to keep the flow of "disinformation" to a minimum.

[YrahG]

Unfortunately, you have been misinformed. Most of the points made in this post are incorrect. To assert that the company you are affiliated with, Shamir, only utilizes position of wear measurements for prescription compensation is one thing. I completely agree that prescription compensation offers only minimal visual benefit to the wearer, as I have described ad nauseam in other threads, including this post from just a few days ago.

But the assertion that position of wear measurements do not influence optical performance, or that other lens manufacturers do not utilize these measurements when designing and fabricating free-form lenses, is completely false. The position of wear can significantly influence optical performance over the entire lens design.

Basic prescription compensation, on the other hand, only improves vision through a narrow region of the distance zone. Further, any eye care professional can apply this form of prescription compensation to any lens, even semi-finished, using free software tools.

I have included an actual optical comparison of three different lenses, which demonstrates the influence of the position of wear. I would also encourage you to review US Patent 6,089,713, which details the use of position of wear measurements when calculating free-form lens designs.


This, again, refers to the same type of prescription compensation that eye care professionals have been applying for years. Free-form lens designs that are truly customized for the position of wear, on the other hand, utilize the vertex, or stop, distance to perform optical ray tracing of a lens-eye model in the position of wear. This is completely independent of any vertex compensation applied because of differences between the refracted and fitted vertex distances.


Actually, for a given base curve, the curvature of the frame can only influence optical performance by changing the position of wear, since decentering a meniscus lens introduces lens tilt. Otherwise, the curvature of the frame has no more effect upon optical performance than the color of the frame.

Now, if you have chosen to substitute a steeper or flatter base curve in lieu of the manufacturer's recommended base curve to achieve a better fit in a frame, thereby violating "best form" optical principles, sufficiently advanced free-form lens designs with full optical optimization can apply the necessary optical corrections over the lens surface.


But, sadly, the opinions often expressed on the Internet do not represent facts. Nevertheless, it would be nice to keep the flow of "disinformation" to a minimum.

Thank you for the patent reference and the reiteration of the differences between prescription and design. I think your software (spectacle optics) makes it not only posible to compensate lenses but the tschernings ellipse makes it possible to see the effects of vertex on best form.

I also don't think that Shamir would endorse the roiginal posters statements. I have worked in a lab in the past but it did not make me that much more knowledgeable about the product, I think in the case of FF this effect is multiplied to an even greater extent.

[Darryl Meister]

I think your software (spectacle optics) makes it not only posible to compensate lenses but the tschernings ellipse makes it possible to see the effects of vertex on best form.

Yes, good point. Although it will not demonstrate the complex optical interaction between position of wear aberrations and the astigmatism of a progressive lens surface, the Optical Analysis module will also allow you to see the effects of viewing angle and vertex distance on optical performance (Spectacle Optics thread).

[YrahG]

I wish more education existed so that it wasn't so that opticians weren't considered the low hanging fruit. Misinformation is how some will make their money.

[OCP]

Unfortunately, I think you have been misinformed. Several of the points made in this post are not entirely accurate. To assert that the company you are affiliated with, Shamir, only utilizes position of wear measurements for prescription compensation is one thing. I completely agree that prescription compensation offers only minimal visual benefit to the wearer, as I have described ad nauseam in other threads, including this post from just a few days ago.

But the assertion that position of wear measurements do not influence optical performance, or that other lens manufacturers do not utilize these measurements when designing and fabricating free-form lenses, is incorrect. The position of wear can significantly influence optical performance over the entire lens design in many cases.

Basic prescription compensation, on the other hand, only improves vision through a narrow region of the distance zone. Further, any eye care professional can apply this form of prescription compensation to any lens, even semi-finished, using free software tools.

I have included an actual optical comparison of three different lenses, which demonstrates the influence of the position of wear. I would also encourage you to review US Patent 6,089,713, which details the use of position of wear measurements when calculating free-form lens designs.


This, again, refers to the same type of prescription compensation that eye care professionals have been applying for years. Free-form lens designs that are truly customized for the position of wear, on the other hand, utilize the vertex, or stop, distance to perform optical ray tracing of a lens-eye model in the position of wear. This is completely independent of any vertex compensation applied because of differences between the refracted and fitted vertex distances.


Actually, for a given base curve, the curvature of the frame can only influence optical performance by changing the position of wear, since decentering a meniscus lens introduces lens tilt. Otherwise, the curvature of the frame has no more effect upon optical performance than the color of the frame.

Now, if you have chosen to substitute a steeper or flatter base curve in lieu of the manufacturer's recommended base curve to achieve a better fit in a frame, thereby violating "best form" optical principles, sufficiently advanced free-form lens designs with full optical optimization can apply the necessary optical corrections over the lens surface.


But, sadly, the opinions often expressed on the Internet do not represent facts. Nevertheless, it would be nice to keep the flow of "disinformation" to a minimum.

Hi Darryl

Sometimes it´s better to overstate the facts to get people understand, but it will not change the point, that Vertex and Panto is more or less impossible to measure correct and are an surce to errors. I see measurement of 15 degrees pantoscopic, when the real measure should be 7. You know just as well as I do, that this could very well be the reasson that the lenses don´t fit prober, and when the client have issues with their new and expensive glasses, you and I (read Zeiss and Shamir)got the problem. My statement is my own opinion offcause, but it will not change the meaning of the contence. Some opticians cant get the personalised lenses like Auto II, the Individual, or the Impression to fitt perfect every time, and I´m quite sure it´s not in the lenses we find the problem, but in the measurements taking by the opticians. To bring down my statement back to reality again, I still think we would all have better lenses by ignoring Vertex and Pantoscopic, or at least use only three different degrees of pantoscopic like 5, 9 or 12 degrees. -and you know just as I do, that you cant use Vertex for anything if you dont got the differences between the refracted and fitted vertex distances. And when do optician take these measures at all, and do you have any guarantee that this measure has been taking 100 % correct? I guess not, and therefore you got an extra surce for mistakes, just like the pantoscopic tilt.

This is my statement and how it works in real life experience. This is different theoretical, but I´m quite sure Shamir and others would agree in real time experience.

Mike

[Barry Santini]

Mike:

I'm not sure why you feel that it's OK to use a set a default pre-set values for Panto (like 5,9, & 12) but it's *not* OK to use an already-substantiated value range of 12.5 to 14.5mm as OK for use as default values (say 13.5mm, yes?) in refractions done with a phoroptor.

I suspect that, as a value, 13.5mm is closer to what would normally be measured in the exam room than what's measured currently with panto at the dispensing desk.

What do you think?

Barry

[Darryl Meister]

Sometimes it´s better to overstate the facts to get people understand

I think your post might be interpreted more as misrepresenting the facts, not overstating them, particularly when you are making some rather specific claims followed by assertions that they are "facts" and "true."

but it will not change the point, that Vertex and Panto is more or less impossible to measure correct and are an surce to errors. I see measurement of 15 degrees pantoscopic, when the real measure should be 7.

Your main point was that these mesaurements do not matter in the first place, which is not accurate. It may be more difficult to take some of these measurements accurately using common dispensing tools, like a PD ruler, but consider the following:

1. Taking position of wear measurements to the best of your ability is still better than not considering these measurements at all, just as taking a less than accurate PD measurement is preferable to using some average value for every single person.

2. There are both manual and digital centration tools available that can take sufficiently accurate position of wear measurements. For that matter, the old "distometer" can take very accurate vertex distance measurements.

Auto II

According to your post, your company's Autograph II lens is not fully customized for the position of wear anyway, which would exclude it from the class of lenses including ZEISS Individual and Rodenstock Impression ILT.

at least use only three different degrees of pantoscopic like 5, 9 or 12 degrees.

That's still better than not measuring them at all and will still only matter if your free-form lens actually takes these measurements into account when calculating the lens design for the patient.

and you know just as I do, that you cant use Vertex for anything if you dont got the differences between the refracted and fitted vertex distances

Again, you are referring to compensation of the prescripton for the vertex distance. While this can be applied in addition to any design modifications based upon the vertex distance, I am referring to the design modifications.

Think of it like this: Suppose you are looking through some point on the lens at 15 mm from the center. Now, at a vertex distance (refracted and fitted) of 13.5 mm, this represents an angle of view of 29.1 degrees, assuming that the center of rotation is another 13.5 mm behind the corneal apex. Now, if you shorten the vertex distance from 13.5 to 7.5 mm, you would be looking through the same point at an angle of 35.5 degrees, which represents a change in the "tilt" of the line of sight relative to the lens of almost 6.5 degrees.

It gets a little more complicated depending upon the initial tilt and curvature of the back lens surface relative to the line of sight, but you should at least see from this example that differences in vertex distance, with or without compensation, can influence oblique astigmatism calculations away from the center of the lens. This is why the near zone in my earlier graphical comparison is "closed off" with unwanted astigmatism compared to the distance zone.

[OCP]

Mike:

I'm not sure why you feel that it's OK to use a set a default pre-set values for Panto (like 5,9, & 12) but it's *not* OK to use an already-substantiated value range of 12.5 to 14.5mm as OK for use as default values (say 13.5mm, yes?) in refractions done with a phoroptor.

I suspect that, as a value, 13.5mm is closer to what would normally be measured in the exam room than what's measured currently with panto at the dispensing desk.

What do you think?

Barry

Hi Barry

What I suggest is to measure the Panto tilt by VISUEL valuation. If the tilt is very oblique select 12, if it´s very vertical use 5, and if it looks normal tilt to the cheek select 9. This is because this tilt is very difficult to measure and because it´s not an fixed measure. It depends on how the person is standing, and therefore I suggest you measure this value visuel. Of cause you cant measure 100% correct this way, but you cant measure this value 100% correct anyway, so it´s an question of ordering realistics as possible.

About the Vertex you need to announce the refracted vertex AND the fitted vertex, because it´s the difference between these two values that makes the pow. comp. BUT it only makes a difference if the power is above 5D and it will only give optical improvement if you measure both values 100% correct, and that is nearly impossible. If your power is -6D and you measure 2 mm wrong, the lenses will NOT work. It´s very easy to measure 2 mm wrong in difference.

The Vertex distance does not change power so much. You can see the difference when you put an client from -3 glasses to contakt lenses. How much does the power change? Maximum 0,25 D in 13 mm difference!!!
The difference between the refracted Vertex and the Fitted Vertex lets say this is only 2 mm. How much would the power change then? I tell you. Aprox. 0,04 D !!! So the Vertex value is in the most cases an theoretical improvement.!!

So, if you do order vertex in 13,5 mm, the supplier does not use this value at all, because they need the refracted value as well to find the difference!

For Darryl. I read and understand your point, but this is still what I claim is "theorethical" improvement. How Zeiss, Shamir or Rodenstock are handling the abberations (because this is actually what we are talking about here) is secrets, and we have all different philosophyes how to handle this. When you exclude the Auto II from the group of individual lenses like Individual, I thank you for that, because we actually think that we are steps ahead these products with Auto II. So your right about this. :bbg:
Shamir are calculating the Vertex and Panto values just as other suppliers does, but that still dont change the statement that it´s sometime unnecessary values.

I hope this could clear out some statements.

Mike

[D.J. Roff, ABOM]

I will have to agree with the original comment, as to the vertex measurement being the least critical. Obviously, we can determine a mathmatical power variance when the vertex is not what the doctor used at the phoropter, but unless the patient has an EXTREMELY high Rx (more than +/-10.00), this rarely comes into play. And the concern with progressive fit is the same with an "individual" lens design as it was with an Omni: the patient wearing it on the end of their nose is like trying to see through a keyhole into a room, with their eye a foot from the door. This is simple common sense, although we're still explaining it to some patients. And no matter how well-fit the lens is, I guarantee it will refuse to sit at the same vertex, plus-or-minus 0.5, for the lifetime of the glasses, just because we wow the patient with our distometer.

The importance of pantoscopic tilt in a progressive fit, however, should not be underestimated. I have had many patients come in with adaptation problems where that one adjustment made all the difference... often saving a non-adapt or even a refund. The patient's near viewing angle, while certainly not static throughout their day, can be approximated, and is an issue of very individual sensitivity... just like "faceform", or "bow" in the frame front. I try to match both of these values to whatever the patient has accommodated to. How well I do will determine how comfortable the patient is with their correction, in many cases... regardless of what lens design I'm fitting.

[Darryl Meister]

So, if you do order vertex in 13,5 mm, Zeiss and other does not use this value at all, because they need the refracted value as well to find the difference!

Once again, you are misrepresenting facts. ZEISS Individual does indeed use the vertex distance in the lens design calculations, as I have already described in detail. Feel free to order and plot two Individual lenses with different vertex distances to see this for yourself. I would recommend doing this before you make further erroneous statements in a public forum.

Please refer to my previous posts, which explain the difference between power compensation for the vertex distance and lens design modifications based upon the vertex or assumed "stop" distance. ZEISS Individual has the entire design modified based upon this distance.

When you exclude the Auto II from the group of individual lenses like Individual, I thank you for that, because we actually think that we are steps ahead these products with Auto II. So your right about this. :bbg: Shamir are calculating the Vertex and Panto values just as other suppliers does, but that still dont change the statement that it´s sometime unnecessary values

You stated in your original post that Shamir's lens designs do not rely on position of wear measurements. If by ignoring these measurements you believe that Autograph II is more advanced than products that perform the extensive calculations necessary to do this, I would say that you are certainly entitled to your opinion, even if I do not agree with it.

[AWTECH]

All of these measurements, are important but to what degree?

Consider wavefront lens designs, it is not pratical for a lens to be used in a frame but can be used for contacts. In a contact for example a off axis of 3 degrees can cause the lens to not work. (The eye certainly moves more than 3 degrees).

How do place a frame back in the same position on the face. (not by the optician but the actual everyday user?) How close can the optician fit the frame to the face each time?

This brings up the point of designing a lens not just for maximum optical performance in a lab but one that will work in the real world.

I believe this tread was started in an attempt to show what is working in the real world use not just in theory.

Does an optimized surface of a lens work when it is mounted 0.5mm wrong by the lab? (I know it shouldn't be, but again real world) etc., etc., etc.

No one wants to wear that frame that is attached to the skull with special titanium screws to guarantee exact position of wear.

Just a few thoughts on the subject to consider.

[Darryl Meister]

Mike, I do not want to come across in this thread as combative or argumentative. And I do not want to discourage you from sharing your thoughts with the rest of the members of OptiBoard as much as possible. My intention in these last few posts has only been to clarify certain claims that you are making regarding products that I happen to be intimately familiar with, like Zeiss Individual, as a guy who spends much of his day calculating and analyzing them.
:cheers:

[OCP]

Once again, you are misrepresenting facts. ZEISS Individual does indeed use the vertex distance in the lens design calculations, as I have already described in detail. Feel free to order and plot two Individual lenses with different vertex distances to see this for yourself. I would recommend doing this before you make further erroneous statements in a public forum.

Please refer to my previous posts, which explain the difference between power compensation for the vertex distance and lens design modifications based upon the vertex or assumed "stop" distance. ZEISS Individual has the entire design modified based upon this distance.


You stated in your original post that Shamir's lens designs do not rely on position of wear measurements. If by ignoring these measurements you believe that Autograph II is more advanced than products that perform the extensive calculations necessary to do this, I would say that you are certainly entitled to your opinion, even if I do not agree with it.

Well, as I have already told, Shamir are calculation the values just like anyone else. BUT that does still not change my personal stance on this.
I did not put down Zeiss or other products, just told you my personal opinion on how to handle these issues and misunderstandings of these two values, and what is theoretichal and what is practical. You do not agree in my statement, and that way we got an constructive debate.

Mike