My lab told me this, that the same progressive when digitized will have a smaller reading area.
Input? Your experiences with this?
My lab told me this, that the same progressive when digitized will have a smaller reading area.
Input? Your experiences with this?
I have not found this to be true. Did your lab have any data to back up that assertion?
What exactly do you mean by "the same progressive, when digitized"?
RT
For example the Physio and the Physio DRX. This is what the rep at the lab told me, I have no data on it.
Absolutely untrue. It's the opposite if it's an IOT- Younger design.
I always have seen Physio Enhanced reading areas looking bigger than Physio DRX designs, but only noticeable in ADDS over +2.50
IMHO it is way way way way more important for the inset of the seg to be in exactly the right place that a patient is looking through than if it is 15-20% wider. If it is not digitally placed with the exact patient's RX and PD in mind than they are not looking out of the exact center of the seg.
I probably don't know what I'm talking about. I like lenses using the Camber technology.
It will often have a lower add power by about 0.12. Perhaps that's what they were thinking of.
So the consensus is that the woman I spoke to was mistaken?
"the same progressive when digitized"
does this mean a conventional cast front side progressive which is then milled on the backside with a milling tool using CNC technology vs the same semi finished lens being surfaced conventionally (whatever conventional means these days).....
OR
A full backside milled progressive which purports to have the same "design" as a similarly named conventional front side lens.....
I think this difference matters, but I might be wrong. And truth is, in answer to your question, I don't think anyone really knows scientifically.
She said digital lenses tended(can't remember her exact wording) to have narrower/smaller reading areas. Not just regular progressives that have been digitized, but I believe she meant in general.
I hadn't heard that elsewhere and wanted to know what others thought.
Placing the progressive optics on the back increases the zone widths by about 10%. This is due to a shorter back vertex distance.
However, by placing the progressive optics on the back, the ocular rotation required to reach the near zone increases, decreasing the near vertical zone height.
The lens designer might correct for this by reducing the corridor length, which reduces the zone widths by about 10%.
The accuracy of your lab reps statement depends on how you define 'smaller reading area'. I'll assume it's the near zone surface area in square millimeters defined by .50 cylinder limits. I think the difference will be very small, probably insignificant.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Which is precisely why HOYA's ID family (Integrated Dual Surface) puts the vertical elements of the progression on the front, and the horizontal elements on the back. Reduces the vertical ocular rotation while also increasing zone width.Placing the progressive optics on the back increases the zone widths by about 10%. This is due to a shorter back vertex distance.
However, by placing the progressive optics on the back, the ocular rotation required to reach the near zone increases, decreasing the near vertical zone height.
RT
Well then, imagine all those folks who took her reasoning at face value and didn't think to ask anyone else.
RT,
When I started fitting the iD, I wrote this in response to a rather knowledgeable consumer at sci.med.vision...
>I was impressed by Hoya's (realistic?) illustration of reduced swim
>effect on stairs. I'm surprised they don't tout it as a safety
>issue. But I wonder if anything in particular is attributable to the
>front-back split of the reading correction. Couldn't a ray-tracing
>program compute a back-only surface with identical performance?
"I'm told that what can be done on two surfaces can also be done on one surface,
at least in regards to power and astigmatic error, and maybe unwanted surface
astigmatism. However, Hoya is not just splitting the Add power on both surfaces,
they're combining two plano cylinders on the front and back surface that sums
the cylinder power to equal the Add power. This is said to reduce skew
distortion, to a degree that can't be done working only one surface."
http://newsgroups.derkeiler.com/Arch.../msg00133.html
My concern is that the iD is not particularly optimized WRT prescription and POW. Does the MyStyle use the same surface configuration, that is, for a +2.00 add, summing a PL +2.00 x 180 and Pl +2.00 x 90, or some combination thereof, what other optimizations are available besides work distance, corridor length, and zone widths?
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Absolutely wrong perception. It's the opposite and it might be slipping tongue statement by lab.
partly true ... not because they are digital. When the Comfort was launched it was still competing against the ST-28 primarily. As the add power increases in every progressive the usable area inherently shrinks (if left alone). The Comfort was the first adaptive design which means the Comfort is a different lens at every add. Their target was to keep the reading area large no matter what. So the lens gets a little harder and the distance width shrinks in every add power.
Fast forward today and most lenses are not reading emphasized, but distance emphasized. What that means is that as the Add power increases the reading and intermediate zones narrow a little, and generally the lens gets a little harder in design as well.
So the more modern designs will shrink the reading in most cases. I am not sure what you mean though when you say "the same lens" when in fact the digital versions are usually different and newer designs, thus they move to a more distance emphasis.
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