Santini - Looks Like He Nailed it!

[John@OWDC]

Just got this email note from someone I had referred to Barry whom I did say was, ..."one of the best at what he does."
It turns out he is either that or, "... at least very passionate."


Hey John!

Just wanted to circle back with you with an update! So I ended up seeing Barry and my experience was absolutely phenomenal with him. I have no doubts that he truly is one of the best at what he does, at the very least very passionate about what he does!

So I think when I originally contacted you, I may have come across as somebody seeking both clearest vision and thinnest lenses, but Barry knew what I was looking for - the clearest vision, but with a frame that produces the thinnest lenses possible given that constraint. Short of having a custom frame, he put me in a Kame Mannen with digital lenses made from CR-39 and a really nice AR coating. This is a titanium frame with a nice thick ridge around the lenses, and he gave it a little forward offset to help hide my power. Not only that, but he got my -8 lens well below 7mm thick! The PD of this frame is so much better than anything else I've been able to find, and while it may not be exactly 57mm, it looks great on me and I can see awesome out of it!

Thanks again for the referral, I'm very happy with the outcome!

[Barry Santini]

Thanks for the referral, John!

FYI: I used a digital SV lens from IOT that is based on their Endless series—but with the PRP at 4mm below the Fitting Point instead at 0mm—as it is with the Endless. This lens was inspired by me in a collaboration with IOT and Cherry Optical Lab. It is called SV 4Sant (Single Vision 4mm Santini). I use digital SV quite a bit. Sometimes the fitting height is better mated to the Endless series. Both lenses are state of the current art.

Yes, he was happy. Now he’s thinking of a pair of sunglasses made of glass. Interesting challenges ahead.

B

[drk]

Good opticianry at it's finest!

[drk]

Time to educate us, Bar-ista.

OK, so...

...lowering the PRP (what traditionally would be called the "optical center", I think) in a frame usually results in minimizing the lower edge thickness, right?

And the visual downside of that (in an isometropic Rx) would be off-axis blur in straight-ahead gaze, through a portion of the lens that is normally used for, say, upgaze. For example, I'm about that blind, myself, and in PALs the 1-2 mm difference between where my eyes sit (the fitting cross) and the "optical center" (PRP) DOES CAUSE a notable blur in the distance vision. I can tilt my head back a teeny bit and get better distance vision, as I find the PRP.

This effect is exacerbated by my using 1.67 (vanity, thy name is drk).

I have a few patients, uber-picky, that notice this effect, and I've even fudged the fitting height slightly higher to "fix" it. (although maybe the inevitable 180 horizon violation is more noticeable, then. There is no good work-around.)


Now, your solution apparently, in this case was for max cosmesis, but you used low index to minimize the off-axis blur?


And IOT was able to make an optical compensation, or no? If they're branding a lens, then probably yes.

Switch to Zeiss, for a moment. Brent has posited that they can somehow disassociate the location of the "intended" optical power of a lens from the PRP (which would be the thinnest point of a non-prismatic lens, I believe). HOW DEY DO DAT?

HOW IOT DO DAT?

Is it as simple as..."hey we can put any power any where in any lens...thickness be darned"?

[Barry Santini]

That’s a mashup of a lot of non-sequitur stuff, drk.

The analogy you started with by referencing your progressives is not the same thing as concerned this buyer.
A few questions into the interview process revealed this person was *very* sensitive to the image degrading effects of abbe. So we settled on using a very high abbe material from the start. Along with his pupillary distance, this dictated frame size and shape. After selecting the Kame ManNen frame and prefitting it, his pupil height—and subsequent fitting height—ended up 4mm above datum (mid-line)—a perfect fit for SV 4Sant. Using Endless would have reduced the resultant imbalance (2.5 diopter binocular difference between the eyes) at primary gaze, but even using my lens, the imbalance is less than 0.8D, and most humans look down more than they look up, so viewing below the primary gaze is always more favorable.

The lesson is the prism reference point is a compromise, no matter which you pick. This client desired maximum optics with more than acceptable cosmetics. And they got it!

Barry

[drk]

So this is an aniso patient?

A few questions into the interview process revealed this person was *very* sensitive to the image degrading effects of abbe. So we settled on using a very high abbe material from the start.

Check

Along with his pupillary distance, this dictated frame size and shape. After selecting the Kame ManNen frame and prefitting it, his pupil height—and subsequent fitting height—ended up 4mm above datum (mid-line)

Typical

Using Endless would have reduced the resultant imbalance (2.5 diopter binocular difference between the eyes) at primary gaze

Or any lens measured traditionally...

the imbalance is less than 0.8D, and most humans look down more than they look up, so viewing below the primary gaze is always more favorable.

So you decided to split some of the downgaze prismatic imbalance by lowering the optical centers? Instead of zero in primary gaze and 2.5 (or whatever) in downgaze, you put about 1^ in primary gaze and 1.5 on downgaze? Not that unusual.

So why did IOT and you mint a new lens to do that and give it your name? Am I missing something that is more elegant that what I just described?

[Barry Santini]

Actually, nothing significantly different here than in the majority of progressive lenses whose PRP is located 4mm below their fitting crosses.

B

[drk]

So IOT has a lens where the prism reference point and the fitting point are co-incident, and you changed that back to the "normal" way? Why would IOT make such a design in the first place?

This brings up a good question that I don't have a concrete answer to...why DO the vast majority of PALs put their PRP about 4 mm below the fitting cross? Is it just the same reason that we drop OC's 3-4 mm in SV, that is, just so the optical axis intersects the sighting/center-of-rotation/whatever when the lens is pantoscopically tilted to maintain a consistent-enough vertex distance for straight-ahead and downgaze? Sounds like it...

[Lensman11]

The prp is usually 4 below for the simple reason that the vast majority of bifocals when frames where normal size and shape not aviator style or similar had the bifocal 3 or 4 mm below center. This would also minimize imbalance at the reading level.

[drk]

Tell me if I'm wrong here, LM11. In a standard segmented MF, the default vertical placement of the distance optical center is about 3-4 mm above the line.

[Kwill212]

So IOT has a lens where the prism reference point and the fitting point are co-incident, and you changed that back to the "normal" way? Why would IOT make such a design in the first place?

ALL IOT single vision and anti-fatigue lenses are fit on center. The fitting cross is on the 180. Well except now,the 4Sant. AFAIK most FFSV lenses are designed and fit this way except for Zeiss which has a 6mm(or 4mm?) difference.

[drk]

Kwill, when you say "fit on center" do you mean that the information that the software needs is where the eye is in the frame, right?

Just because you provide that "fitting height" it doesn't mean that's where the "optical center/PRP" ends up, right? Different companies with different math/designs will do what they want, right?

I tell my optician (yes, I "TELL" her...I'm a misogynist OD employer pig) that if it's a branded lens, all we ever need to do is provide the split pd and dot the pupil center. Let the software do the rest. Including branded SV designs.

(This is in contradistinction to us designing our own lenses using wrap formula compensations, adding prism for tilt, outsetting p.d.s for wrap--and now moving OCs and segment heights for high prism amounts..whew! But, again, every time you order a traditional SV lens and drop the OC by 1mm per 2 degrees of panto, you are providing your own POW compensations, which is a new take on an old idea.)

[Kwill212]

Kwill, when you say "fit on center" do you mean that the information that the software needs is where the eye is in the frame, right?

When I say fit on center, I mean the fitting point and prp are the same point.

Just because you provide that "fitting height" it doesn't mean that's where the "optical center/PRP" ends up, right? Different companies with different math/designs will do what they want, right?

The fitting point should end up at the measured fitting height. Pupil center. Whether or not that is where the PRP is depends on the lens manufacturer and design.

I tell my optician (yes, I "TELL" her...I'm a misogynist OD employer pig) that if it's a branded lens, all we ever need to do is provide the split pd and dot the pupil center. Let the software do the rest. Including branded SV designs.

If by "branded" you mean compensated freeform lens, yes. If not, Martin's Rule applies.

[drk]

Thank you. Keep it coming...

...now, WHY would IOT put a PRP on the pupil center when (as you say) "Martin's Rule" would dictate otherwise?



(P.S. Did you know that Optiboard gets a lot of ink on the web with search terms like "Martin's Rule"? GO OPTIBOARD! https://www.optiboard.com/forums/sho...rmula-for-Tilt)

https://www.2020mag.com/article/pant...%20progressive.

[drk]

Barry, to decipher what you call "non-sequitur" thinking, remember this thread...https://www.optiboard.com/forums/sho...a-change/page5

[Kwill212]

Thank you. Keep it coming...

...now, WHY would IOT put a PRP on the pupil center when (as you say) "Martin's Rule" would dictate otherwise?

Martin's Rule applies to non-compensted lenses. IOT does not make non compensated SV lenses.

I can not speak to their design intention with regard to PRP/fitting height vs other companies. It seems like a 4 or even a 6 drop SV would have better cosmetics for most fits in current frame styles. My guess would be ease of use and less confusion for the McTicians out there. I had one lab tell me that they don't engrave FFSV lenses because their accounts didn't like SV lenses to be engraved! So there are people ordering compensated lenses, purposefully asking them not be engraved, then blocking and edging them with the prescribed axis, thus completely ruining the intended lens design. It's a bananas world out there drk.


It seems you could accomplish a "4 drop" SV lens by calculating the vertical prism and surfacing it in the opposite direction. Just prism thinning of a sort. So for a -2.50 fit at the pupil, if you want a 4 drop lens, request 1D BU. A I have ordered and dispensed FFSV lenses with yoked BU prism for this purpose before with no ill effects. I have no idea if it is as simple as that to make a 4Sant, or if IOT needed to recalculate the compensation for the lens design as well.

[Barry Santini]

Martin’s rule exists only to align the image shell of a conventional Corrected Curve SV lens to an eye’s far point sphere. It assumes a standard fitted vertex distance of 13.0-13.5mm. It does jot apply to FF SV…unless you never forget to think binocularly:

1. keep the VD of the rear lens surface as unvarying as possible for most lens gaze angles.
2. Thinking binocularly, the PRPs are positioned below the eye pupil to reduce imbalances in Anismetropic and moderate to strong oblique cyl corrections. Think multifocals have Two masters to consider.
3. NEVER EVER say “fit on the 180” unless you mean at datum. Any other evolved meaning is wrong. Correct thyself.

B

[drk]

Yes, Kwill (and Barry), and I did put it in "quotations" because these simplistic (I guess) tilt formulas have been replaced by sophisticated ray tracing (whatever that actually is...sounds like "iterative design" by a computer).

But the physical point still stands...tilting a lens requires a compensatory power change to deliver the right optics. So, Martin's Formula or Ray trace, there has to be a change made.

It seems we will never know why IOT does it on pupil center. Barry has had a chance to talk to them, apparently, but he hasn't yet explained why they do it. He just says he's had them "undo" it, in order, apparently, to redistribute an anisometropic prismatic imbalance. Which, as I said before (even when I erroneously thought we were talking about cosmetic appearance and lowering the PRP closer to the frames datum line) is GOOD OPTICIANRY.

[Barry Santini]

IOT has said that ODs “do not like” (the impurity) of any prism—let alone imbalance—in the primary gaze.

B

[drk]

Interesting. Thank you for that.

Question: would that be a valid concern?

[drk]

Here's another form of that question:

And the visual downside of that (in an isometropic Rx) would be off-axis blur in straight-ahead gaze, through a portion of the lens that is normally used for, say, upgaze. For example, I'm about that blind, myself, and in PALs the 1-2 mm difference between where my eyes sit (the fitting cross) and the "optical center" (PRP) DOES CAUSE a notable blur in the distance vision. I can tilt my head back a teeny bit and get better distance vision, as I find the PRP.

This effect is exacerbated by my using 1.67 (vanity, thy name is drk).

[Lensman11]

Sometimes I think I am having a nightmare reading the replies from some of the opticians. Very similar to the requests I used to get when I owned my own lab. Kudos to Barry S actually knowing what he is talking about one of a handful knowledgeable dispensers. Barry uses his real
name so we all know who he is I choose not to do that. I actually know Barry and did lab work for him many years ago.lab was on eastern Long Island.
To answer DRK the oc on multi focal was always placed in the geometric center of the lens and the majority of the time the seg was placed 3 or 4 mm below the center. When aviator shapes and similar came into vogue segs were routinely dropped 10 mm causing a whole new series of problems that most optician had no idea what caused them or how to remedy the situation.
how

How can you possibly call grinding vertical prism in single vision lens prism thinning not even a minute relevance of being correct. Prism thinning was created to make the thickness on a progressive as equal as possible on the top distance portion and bottom add portion to enable you to have an overall thinner lens. The first go round was prism thin with half the add power so a 2.00 add got one prism it was better but not optimal I wrote the software that optimized the amount of prism by using the height and lens shape to find the best amount of prism. The amount of prism is different as the height changes as well as the shape. Under some circumstances you need base up prism instead of base down to create the thinnest lens.
I have actually been told by several opticians that if you grind prism in a lens it different then decentering to achieve the prism again no understanding of basic concepts.

[drk]

To answer DRK the oc on multi focal was always placed in the geometric center of the lens and the majority of the time the seg was placed 3 or 4 mm below the center. When aviator shapes and similar came into vogue segs were routinely dropped 10 mm causing a whole new series of problems that most optician had no idea what caused them or how to remedy the situation.

I hesitatingly and semi-humbly call "bullshirt" on this one, and here's why: seg lines are always in relation to the pupil, not the bottom of the eyewire. If it was the 46 eye Ronsir, sure, the seg height will be written as a 14, and if it's the 72 eye Big Swinger Groovy, the seg height will be 28, but what does that have to do with the distance of the line from the optical center? That should have stayed constant throughout the ages.

No, I think it must have had to do with the prism splitting issue or something else.

[Lensman11]

DRk
You 100% correct the problem arose because the dispensers did not understand about the need to order the oc placement they did not do this before and did not understand what was going on. If you routinely made the oc 3 above the seg line you could produce imbalance in the distance. A compromise was in order but you had to understand that sometimes the compromise did not satisfy the imbalance in the distance or the reading and tell the patient their frame choice won’t work with their Rx. Even yoked prisms bother some people so it was pretty much agreed never prism thin more tha 2.5 diop even if higher prism would result in a thinner lens.

[Lensman11]

Forgot one more point moving oc away from the geometric centric will have an effect on the thickness as well. Moving the oc down to be
closer to seg is no different than decenter the lens. Of course depending on the Rx this could be dramatic.