Help with a bet on the OC

[Paul Smith LDO]

Not just 'pupil heights' though, is it? It's more like 'pupil point'. Which is a term I might just well start using, provided I don't fall victim of the emboldened, chastising typography as seen above...

Clarification of proper terminology is far from chastising any said individual and if the members of the board can help with clarification is that not what we are all here to do. I prefer to call a spade a spade, that's why it is designated as such.

[Speed]

So with digital SV lenses you don't drop the OC based on the panto?

AH! Someone has read an opticians book. Good to see.

[standarduck]

Clarification of proper terminology is far from chastising any said individual and if the members of the board can help with clarification is that not what we are all here to do. I prefer to call a spade a spade, that's why it is designated as such.

My comment was meant as tongue in cheek really, so apologies for the miscommunication...

As for the terminology, I stand by what I said - when you mark a pupil in a frame, you are not taking 'pupil heights'. It's a composite measurement including both vertical and horizontal components. Shouldn't it have a name on its own? (perhaps it does - if so, someone tell me).

[Barry Santini]

Semantics perhaps - but no wholesale lab I've ever worked with called this measurement anything but OC. In the end, we need to know how to take this measurement consistently (on pre-adjusted frames), and the strength of the SRx (as it relates to this measure) truly should be the least of our concerns.

In the immortal words of the Stay Puft marshmallow man - Just Do It!

Yes...ALL labs continue to do this..and it's obsolete and WRONG!

B

[Uilleann]

Yes...ALL labs continue to do this..and it's obsolete and WRONG!

B

Go git 'em Big B!

[Robert Martellaro]

At what power do you start to sell "digital" and asheric's?

When it's good for the individual client.

Isn't why we add Panto to progressives to help the patient "get to the reading" faster because it artificially raises the OC in the lens by changing the angle it is being viewed out of?

Slower with more panto, but the primary reason is to decrease the vertex distance at near, increasing the zone width at near, allowing for an alignment that more closely matches the intended design envisioned by the lens designer/team.

Not just 'pupil heights' though, is it? It's more like 'pupil point'. Which is a term I might just well start using, provided I don't fall victim of the emboldened, chastising typography as seen above...

The Germans seem to like fitting point (height). Optical center height is still valid, and usually has a different magnitude than the fitting point height. Seg height is acceptable for segmented multifocals.

Use Martin's Tilt Rule (- 1mm OC below Pupil height for each degree of Pantoscopic angle)

.5mm per 1˚ of tilt.

So with digital SV lenses you don't drop the OC based on the panto?

It depends on the design. I have fit free-form surfaced backside aspheric/atoric lenses that had zero optimizations or customizations. These are fit the same as semifinished lenses.

The more optically capable designs have mostly fixed positions for the pole, PRP and in their relationship to the fitting height, although sometimes we have some control over the prism thinning and the subsequent position of the vertical OC position.

[Barry Santini]

Robert's the man!

[Tallboy]

And the wutang master has spoken.

Gong

Thanks for teaching me so much Robert.

[ml43]

Yes...ALL labs continue to do this..and it's obsolete and WRONG!

B

It's mostly because that's what most lab software's call them.

Lab vs dispensing.

if the glasses never touch a patient, it's not a pupil height, it's an OC height.

reverse argument could be made for FPD, though.

[Barry Santini]

It's mostly because that's what most lab software's call them.

Lab vs dispensing.

if the glasses never touch a patient, it's not a pupil height, it's an OC height.

reverse argument could be made for FPD, though.

Gotta say I disagree.

B

[ml43]

Gotta say I disagree.

B

In industry, there will always be multiple terms for describing the same thing.

Positive cylinder vs negative cylinder is a perfect example.

As long as we all know what we are referencing, there is no point in being pedantic about it.
Time is better spent on other things.

edit:
Just for laughs. If you made a pair of glasses for someone with one glass eye that had a balanced Rx.

Would you specify a pupil height for one eye, and an "OC" height for the glass eye?

[Dave E]

In industry, there will always be multiple terms for describing the same thing.

Positive cylinder vs negative cylinder is a perfect example.

As long as we all know what we are referencing, there is no point in being pedantic about it.
Time is better spent on other things.

edit:
Just for laughs. If you made a pair of glasses for someone with one glass eye that had a balanced Rx.

Would you specify a pupil height for one eye, and an "OC" height for the glass eye?

Have you ever seen this pal in one eye and a sv in the other and they only take the seg ht and not the oc ht.

[Barry Santini]

In industry, there will always be multiple terms for describing the same thing.

Positive cylinder vs negative cylinder is a perfect example.

As long as we all know what we are referencing, there is no point in being pedantic about it.
Time is better spent on other things.

edit:
Just for laughs. If you made a pair of glasses for someone with one glass eye that had a balanced Rx.

Would you specify a pupil height for one eye, and an "OC" height for the glass eye?

If they never touched a patient, it would be an MRP.

B

[MakeOptics]

http://www.thevisioncouncil.org/site...l%20June16.pdf

Some of the terms being thrown around are deprecated or never really were in vogue. The closest I have been able to find that closely matches the OP's question is Roberts response which refers to the Fitting Point and according to the standards Fitting Cross.

[Jacqui]

ALWAYS put the OC in front of the pupil !!!!! End of conversation.

[Slim]

At what point would you NOT edge at the fit height?
I ask because a while ago i had a pt that was something like a -5.50 and a -.3.00
She wore them so the OC or "PH" lol was near the top ( 5mm below the top )
When she put them on she had the dreaded trapezoid effect. I re made them with the OC centered and all was good.

My guess is that the diff of 1.50 diopters between the two was giving her issues, as I believe she also complained of it not feeling right as well (been a year since the pt)

[Paul Smith LDO]

The final decision as to both the horizontal and vertical placement ultimately rests on the optician. Utilization of material, lens design, knowledge, and patient satisfaction are what ultimately constitutes the success of properly made eyewear. Resolution comes with clarity of optical terminology and basic principles of optical physics. To those on the board who continue to reiterate these concepts keep up the good work as there are many folks dispensing who require assistance from you.

[MakeOptics]

The final decision as to both the horizontal and vertical placement ultimately rests on the optician. Utilization of material, lens design, knowledge, and patient satisfaction are what ultimately constitutes the success of properly made eyewear. Resolution comes with clarity of optical terminology and basic principles of optical physics. To those on the board who continue to reiterate these concepts keep up the good work as there are many folks dispensing who require assistance from you.

+1, I feel like this board is building the tower of babel.

[standarduck]

ALWAYS put the OC in front of the pupil !!!!! End of conversation.

What about alterations due to the pantoscoptic tilt?

[Barry Santini]

What about alterations due to the pantoscoptic tilt?

Following.

[standarduck]

Following.

I'm sorry, I'm not sure I understand your post.

[Barry Santini]

I'm sorry, I'm not sure I understand your post.

Your last question was EXACTLY what I wanted to know. So I am now "following" with attention this thread!

B

[revein]

I don't take OC with low powers if an RX lens is required due to insufficient lens diameter, whereas you could get by with a stock lens with the OC vertically in the center of the frame. There is no price difference for us between stock and RX lenses, just that RX might take a week longer and customers appreciate swiftness.

A good example would be from today. Customer wants sunglasses with powers of something like -3.50/-4.25, PD of 29.5/29.5. Maximum lens diameter for that type of a 1.67 lens we have is 75mm which was a tiny bit too small. Stretched the PD to 30.5/30.5 and worked fine, no biggie :)

[Boldt]

I don't take OC with low powers if an RX lens is required due to insufficient lens diameter, whereas you could get by with a stock lens with the OC vertically in the center of the frame. There is no price difference for us between stock and RX lenses, just that RX might take a week longer and customers appreciate swiftness.

A good example would be from today. Customer wants sunglasses with powers of something like -3.50/-4.25, PD of 29.5/29.5. Maximum lens diameter for that type of a 1.67 lens we have is 75mm which was a tiny bit too small. Stretched the PD to 30.5/30.5 and worked fine, no biggie :)

Wile not a fan of the PD stretch, I've used it when I've had to, but with a script like that you'd be giving them a bit of prism. They may not say anything about because they don't know about it, but I've had many people be floored when I do an OC on anything over a -2. A week of waiting might be worth it to them.

[MakeOptics]

What about alterations due to the pantoscoptic tilt?

CENTER, OPTICAL: The point on the front surface of a lens intersected by the optical axis of the lens. This point is free from prismatic effects.

That is the strictest definition according to the Vision Council, the Optical center should be displaced:

COR = Center of rotation (mm) average 13.25mm
VD = Vertex distance (mm) average 13.75mm
CT = Center Thickness (mm) average 2.0mm

displacement = sin(panto) * (COR+VD+CT)
displacement = sin(1) * (13.25 + 13.75 + 2)
displacement = 0.017452406 * 29 = 0.506119787

for every degree 0.51mm is the average which is where the expression 1mm for every 2 degrees comes from, but those averages are using old averages from an AO tech publication, most lenses nowadays are aspheric and fit flatter + wrap lenses often crash against the lashes indicating varying VD measures, I would guesstimate 12mm as the average vertex distance, and most lenses nowadays are on average 1.5mm CT, reconfigure and the numbers change a bit:

displacement = 0.017452406 * (13.25 + 12 + 1.5)
displacement = 0.017452406 * (26.75) = 0.466851872

Rounded that gives 0.47mm for every degree, doesn't seem like much but myopes and hyperopes have varying lengths to the COR which wasn't adjusted in the previous measures. Still not much of a difference except we now have accepted methods for computing and compensating for these measures.

Given a 15 degree tilt:

Older = 0.506119787 * 15 = 7.591796805
Newer = 0.466851872 * 15 = 7.002778083

Now we're seeing 0.5mm difference which starts to look significant, of course with COR factored in you could see a bit more of a bump. Realistically this is not a exercise you will compute for each patient long form, but with current technology this is going on in the algorithms in the equipment behind the scenes, making for much more sophisticated power compensations.

So your OC if it still remains on the lens (another topic of discussion) should be displaced as such from the fitting cross (pupil height). (yes a SV lens can have a fitting cross, it's just a reference to a point on the lens and that is standard definition)