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My optician asked a good question, and I think I gave the right answer. But I thought it would be a good brain exercise for Optiboard.
Q: What is the benefit of "digital" designs for SV spheres? (No cyl, no add. Say, -1.00 DS, +1.00 DS, -6.00 DS, +4.00 DS)
[QUOTE=drk;554519]My optician asked a good question, and I think I gave the right answer. But I thought it would be a good brain exercise for Optiboard.
Q: What is the benefit of "digital" designs for SV spheres? (No cyl, no add. Say, -1.00 DS, +1.00 DS, -6.00 DS, +4.00 DS)[/QUOTE
As long as you hold your head real still, and look straight ahead through the OC, and don't use your peripheral vision, then no benefit at all.
But then, under those circumstances, a pinhole would work pretty well also.
Compared to spherical/aspheric semi-finished or finished ± 1.00 DS, no difference due to inconsequential degrees of marginal astigmatism.Quote:
Originally Posted by drk
There are incremental benefits over ±2.00 DS (generally more dioptric power = more optical error), especially when the values for tilt around the x-axis and y-axis increases, with or without non-default values (about 13mm) for vertex distance. The software must be capable of correcting for optical errors due to position of wear, non-optimal base curves, etc.
Attempt to assess your client's tolerance for blur, on and off-axis. Use the more refined solution when in doubt.
Why we don't want to use a spherical 1.67 index lens for a +6.00 DS Rx. That's in addition to 0.3∆ of chromatic aberration off-axis blur.
I think you both are on a different track than I was thinking.
I answered that it's "the same benefit" as we have come to expect from the older aspheric molded front lenses.
a. if it's a low power lens, nada.
b. if it's a higher plus, you get lens flattening.
c. if it's a higher minus, you get minimal edge thinning (and we never cared much about that).
I'm operating under the principle that aspheric lenses just correct the slop induced by using flatter front curves (for plus lenses).
You guys are operating under the principle that off-axis viewing can be improved upon, compared to best-form spherical lenses.
Both are right, I believe. Which do you think is a more fundamental consideration (i.e. the one that would compel you to use a good digital design for a high power sphere)?
Not the same.Quote:
Originally Posted by drk
Yup.Quote:
a. if it's a low power lens, nada.
All powers would have flatter BCs. We'll probably have better results if we aphericize the meatiest curve, that is, the ocular curve for minus, and the BC for plus. But it's cost less to use spherical BCs working that back only, with a few exceptions.Quote:
b. if it's a higher plus, you get lens flattening.
A free-form generator can produce the asphericity on the back of a minus lens, with more effect than using a front apheric, where the BC is already pretty darn flat (+.50 to +1.00).Quote:
c. if it's a higher minus, you get minimal edge thinning (and we never cared much about that).
It also decreases magnification and minification, sometimes significantly. Maybe a decrease in vertex distance, depending.Quote:
I'm operating under the principle that aspheric lenses just correct the slop induced by using flatter front curves (for plus lenses).
It can be close if the lens comes in narrowly spaced BCs, 1 D or slightly less, which is expensive to stock, and is unnecessary now that we can custom design a lens on a free-form platform. And if we need a slightly steeper or flatter BC, FF says yes, can do (software dependent).Quote:
You guys are operating under the principle that off-axis viewing can be improved upon, compared to best-form spherical lenses.
Note: Best form for hi-index lenses, without aspherisizing, results in very steep curves. For example, a +3.50 DS 1.67 requires a +10.25 BC, 1.74 index best form would be +12.25 BC. I doubt that most people on optiboard have seen a +12 base.
Another example of FF superiority is with the aspheric pole/oc position. Semi-finished/finished requires the pupil heights to be lowered to align the optical axis with the center of rotation, not necessary with FF, minimizing vertical prism imbalance (when present due to dissimilar powers at ninety) with slightly less chromatic aberration to boot.Quote:
Both are right, I believe. Which do you think is a more fundamental consideration (i.e. the one that would compel you to use a good digital design for a high power sphere)?
If the lens has optimizations beyond aspheric's/atoric surface designs, we should expect slightly better visual performance at all angles of gaze, depending on the degree of power and tilt. For example, -5.00 DS wrap 10˚ panto 10˚, -4.62 -0.25 x 46 .25∆ BI needs to be surfaced to match the prescribers intent.
Best regards,
Riobert Martellaro
Hmm...a lot to digest.
I will be back for mansplainin' sometime soon! :)
WOW! Now there’s a loaded and obfucacious term.Quote:
Originally Posted by Robert Martellaro
If anyone can, with confidence, ascertain this by looking at a typical Rx, more power to you.
B
I've been listening to politicians so much lately that I'm beginning talk like them.Quote:
Originally Posted by Barry Santini
I didn't consider that. So, free form SV for minus can have a bit more of an edge thinning effect than the old molded ones. Huh. Generally FFSV is not expensive, but I do wonder what kind of numbers we're talking. 0.5mm? (I know, dependent on the variables.) But are we talking 1 mm in many cases, or "chump change"?Quote:
A free-form generator can produce the asphericity on the back of a minus lens, with more effect than using a front apheric, where the BC is already pretty darn flat (+.50 to +1.00).
So...when we order, say, Walman's house FFSV (or even VSP's Unity), are we going to get dual-digitally-surfaced-from-puck, or are we going to get it from a semi-finished blank? What goes on, out there?Quote:
It can be close if the lens comes in narrowly spaced BCs, 1 D or slightly less, which is expensive to stock, and is unnecessary now that we can custom design a lens on a free-form platform. And if we need a slightly steeper or flatter BC, FF says yes, can do (software dependent).
This is news to me, as well. I am probably guilty of ordering FFSV with a 3mm drop-below-pupil-center MRP, instead of a "fitting height". Dang. As a flaming myope with 1.67 PALs, I don't like looking 4mm above the PRP due to standard PAL fitting procedure. I get aberration, and find myself tilting my head back with distance viewing for better optics. (I fit myself high to help offset this.) But SV patients (and anisometropes) would greatly benefit.Quote:
Another example of FF superiority is with the aspheric pole/oc position. Semi-finished/finished requires the pupil heights to be lowered to align the optical axis with the center of rotation, not necessary with FF, minimizing vertical prism imbalance (when present due to dissimilar powers at ninety) with slightly less chromatic aberration to boot.
But what about this whole "optic axis intersecting the center of rotation of the eye" thing? Is that just for a sphero/cylinder lens and it merely "averages" the worse optics between straight-ahead gaze and downgaze? Does this mean that FFSV can compensate for optics on downgaze without compromising the straight ahead gaze?
IOW, you're saying that one of the nice things about FFSV is automatic POW compensation. Yeah.Quote:
If the lens has optimizations beyond aspheric's/atoric surface designs, we should expect slightly better visual performance at all angles of gaze, depending on the degree of power and tilt. For example, -5.00 DS wrap 10˚ panto 10˚, -4.62 -0.25 x 46 .25∆ BI needs to be surfaced to match the prescribers intent.
Typical Barry.Quote:
Originally Posted by Barry Santini
Simply put (and you know this), the numbers on the Rx pad is the "prescriber's intent". No more, no less. It's not mysticism.
About 3% to 5% more (compared to front aspherics) according to D. Meister's Optical Analysis program. A tad more for high minus (>8 D), without lenticulation.Quote:
Originally Posted by drk
Puck, semi-finished, same animal. Although the blank might have been formed in digitally generated mold, it's a stretch to call it dual FF/digital. That talk is for the marketing dept.Quote:
So...when we order, say, Walman's house FFSV (or even VSP's Unity), are we going to get dual-digitally-surfaced-from-puck, or are we going to get it from a semi-finished blank? What goes on, out there?
Pupil height. Take 'em on all RXs except spherical ±0.50 D. It's good practice, minimizes VI and other aberrations, and only takes a minute or so to measure on a preadjusted frame. Lower the OC .5mm per one degree of panto tilt for non-optimized lenses, aligning the lens axis with COR.Quote:
This is news to me, as well. I am probably guilty of ordering FFSV with a 3mm drop-below-pupil-center MRP, instead of a "fitting height".
That's not right. 4mm shouldn't generate enough CA at this power. Try a 1.60 refractive index in the same package to rule that out. If you were anyone else I'd suspect overminusing or a hyperopic shift.Quote:
Dang. As a flaming myope with 1.67 PALs, I don't like looking 4mm above the PRP due to standard PAL fitting procedure. I get aberration, and find myself tilting my head back with distance viewing for better optics. (I fit myself high to help offset this.) But SV patients (and anisometropes) would greatly benefit.
Probably better optics at all angles of gaze.Quote:
But what about this whole "optic axis intersecting the center of rotation of the eye" thing? Is that just for a sphero/cylinder lens and it merely "averages" the worse optics between straight-ahead gaze and downgaze?
More better, with the best software, keeping in mind that FF generators can make "dumb" lenses also.Quote:
Does this mean that FFSV can compensate for optics on downgaze without compromising the straight ahead gaze?
It places the OC on the primary gaze, without compromise, over a wide range of tilt and wrap values. Si.Quote:
IOW, you're saying that one of the nice things about FFSV is automatic POW compensation. Yeah.
Best regards,
Robert Martellaro
I'm trying to be clear, and make sweeping generalizations.Quote:
Originally Posted by Robert Martellaro
If you're saying 5% more than a little, then I'll just neglect this.
So if they're going to do a FFSV, you're saying they choose a "puck" with an approximate certain base curve? And then surface the front and the back?Quote:
Puck, semi-finished, same animal. Although the blank might have been formed in digitally generated mold, it's a stretch to call it dual FF/digital. That talk is for the marketing dept.
Agree there. Specify for everything to be consistent. But dropping for panto on FFSV not needed?Quote:
Pupil height. Take 'em on all RXs except spherical ±0.50 D. It's good practice, minimizes VI and other aberrations, and only takes a minute or so to measure on a preadjusted frame. Lower the OC .5mm per one degree of panto tilt for non-optimized lenses, aligning the lens axis with COR.
It's true. I now know that I'm too picky for high index. It's mid-index for me.Quote:
That's not right. 4mm shouldn't generate enough CA at this power. Try a 1.60 refractive index in the same package to rule that out. If you were anyone else I'd suspect overminusing or a hyperopic shift.
Thanks!
remember molded minus aspherics usually have at least
.5 mm difference in center thickness compared to surfaced lenses, and often 0.8mm less. Unless FFSV is including some lenticularization it generally will not be thinner than radially aspheric molded lenses. But there are so many other peripheral vision benifits. My current main pir is molded aspheric though
Somewhat off topic, but taking a pupil height also reinforces to the patient that they need more than just a generic PD to get properly fitted glasses. I measure OC height on every patient for this reason.Quote:
Originally Posted by Robert Martellaro
Help me out here. I do a height with my Ray ban googles polar suns -1.50 ou with a 48 mm vertical, height is +/- 40 mm. When I look down at my golf ball height is now+/- 20 mm. I now have 3.0 diopters base up prism. Now what?Quote:
Originally Posted by AngeHamm
1. You would be looking through yoked prism looking down. No harm, no foul.Quote:
Originally Posted by Don Gilman
2. You made a bad frame choice when you got a frame with your pupils sitting 8mm from the top of the frame. :giggle:
Keep in mind that the difference in thickness due only to refractive index between 1.60 and 1.67 is only ((1.60 - 1.00) / (1.67 - 1.00) = 0.90) 10% thinner.Quote:
Originally Posted by drk
As stated, it's semi-finished, meaning molded front, surfaced back.Quote:
So if they're going to do a FFSV, you're saying they choose a "puck" with an approximate certain base curve? And then surface the front and the back?
Unless otherwise specified by the lens manufacturer, we should bisect the corneal reflection in the primary gaze. The software takes it from there.Quote:
Agree there. Specify for everything to be consistent. But dropping for panto on FFSV not needed?
Your welcome. Ditto on the chroma sensitivity, although I'm a few diopters less minus than you. Our only saving grace is possibly higher IQs, and we're the goto folks for splinter removal.Quote:
It's true. I now know that I'm too picky for high index. It's mid-index for me.
Thanks!
Best regards,
Robert Martellaro
It’s true, Myopes test higher on most I.Q. Tests. But counter-research ( optical24/7 research think tank...) shows Hyperope’s are more out going, have more friends, get invited to more parties and are generally better looking than Myopes...:bounce:Quote:
Originally Posted by Robert Martellaro
Quote:
Originally Posted by optical24/7
I guess that explains myself with my emmetropic Rx with a mild add. I am a "special" cave troll :(
Hey, what about us mixed astigmatic presbyopes? I feel left out!
Don, your golf buddies called.Quote:
Originally Posted by Don Gilman
They said your golf game problems are not measured in millimeters. They said they should be measured in 100s of yards.
JUST SAYIN'
Attention all Optiboarders. Attention all Optiboarders.
We have a paradigm shift (for me).
You know how PALs are branded? I don't say "hey, patient, you need a PAL" I tend to get a little more geeky than that, and will discuss the brand, etc. Let them understand the sciency-nature of what we do. These aren't generic. "Hey, man, you're wearing a (insert brand here) progressive with digital design (whatever) with blah, blah, blah.
Well, if you think about it (and Robert's correcting me in that we just measure a fitting height/POW, and the computers do the rest) that these FFSV are pretty dang high-tech, too; in the vicinity of PALs.
I'm going to prescribe and promote them as such.
So the answer to my optician to the original question will now be: "Optics, baby. Optics!"
Am I behind the curve on realizing this?
Not when your puttingQuote:
Originally Posted by drk
Then you have a weird putting stance. You don't need to stand tall at address, like with your driver. Put that head down, man!