If I analize the glasses of a patient is wearing an meassure the prescription of the lenses read with a lensmeter, and also measurement the panto and facial wrap, how do I calculate the equivalent prescription for panto=0 and facial wrap = 0?
If I analize the glasses of a patient is wearing an meassure the prescription of the lenses read with a lensmeter, and also measurement the panto and facial wrap, how do I calculate the equivalent prescription for panto=0 and facial wrap = 0?
If I'm reading your question correctly: What you're seeing in the lensometer IS the effective power for a 0 tilt / 0 wrap.
Are you trying to determine effective power of the lens adjusted for tilt/wrap values?
Maybe I did not explain clearly.
Lets try this way.
When you are going to make glasses for a patient you have the Rx dispensed by the Dr. and you meassure pano and panto of the frame and with this information a new Rx is calculated. This New Rx is send to the lab to make the lenses.
The lenses come from the lab and you meassure then with the lensmeter. They will have the Rx you calculated considering pano and panto.
Having the Rx (the one send to the lab) and having pano and panto how do I know the Dr. prescription?
Last edited by MIOPE; 06-30-2017 at 01:30 PM.
The lab should send you the comp'ed values. If not use this....
http://64.50.176.246/tools/tilt.php
Are you asking how to solve for the original Rx, given the compensated powers and POW measurements, as in, working backwards? Why would you do that? Are you trying to duplicate the powers for an additional pair of glasses? Like, you have what you believe to be wrap-compensated sunwear in your hand, and you want to "duplicate the Rx" in a pair of dress frames?
This calculator starts with the Dr. Prescription and according to the amount of pano and panto it will calculate the prescription thar should be grinded.
What I want is to go in a reverse direction.
Having the grinded prescription, pano and panto, estimate the Dr. Prescription.
Correct DRK. I need to duplicate the lenses in a frame with different pano and panto.
Lensmeter of actual lenses.
OD -6.50 -2.75 x 180
OI -7.00 -3.00 x 180
Dv 9mm panto=9 pano=5
You would have to look up the Martin's tilt formulae and use algebra. It's probably straightforward (but I sure ain't doin' it...).
It's not too bad, reverse engineering it is a chore. For all that time and effort, tracking down the prescribing doc for the original Rx is a lot easier.
The lensometer return sure doesn't seem like a digitally compensated Rx, so I bet the tilt differential can be simplified, and the new frames can't afford much more wrap anyway with this Rx.
http://calculators.brent-mccardle.org/pow.html
Use this link to get the effective calculation. This calculation gives you the effective power if not compensated. Keep in mind the calculations from the lab use more data, the calculations on the link above do not consider shape.
B-man:
What's the explanation of what "effective power" is?
I think I know what "compensated" is...you put in the "flat" Rx and get out the lens powers in a curved frame that will provide the "flat Rx".
My wife's out of town and I'm nerding off to this thread. *munching popcorn*
If I remember correctly, compensated power insures that the effective power equals prescribed power for any given frame/lens combo.
Lensgrinder could probably provide the geek-ed out version of this.....
It's late and the vodka is kicking in. Too much math for me.
Thanks Lensgrinder.
The effective power on this calculator seems to be what I need.
But do not know why sometimes this calculator gives axis 61.18 as result when the input Rx axis is 180.
Last edited by MIOPE; 07-01-2017 at 03:24 AM.
OK, I've had a coffee.Originally Posted by MIOPE
Looking at that data, I'd say you have an uncompensated Rx, because those are standard POWs (well, a little close-fitting vertex, but that's easy).
Just feed that stuff into the wrap compensator as the "flat Rx".
My question for you: Are you going into a significantly greater frame wrap? If not, you're splitting some serious hairs, here.
The new frame is not too different to the one he is wearing. It has pano=5 panto=9. This time the patient is ordering IOT compensated single vision. This is a freeform with ray tracing technology. He expect something better that his old glasses. And he has very good vision with the old glasses.
So I am paying attention to every detail.
A difference of 0.12 might do a difference. I estimate that
-6.62 -2.95 × 180
-7.13 -3.22 × 180
Is very close to the equivalent prescription with panto=0 pano=0
Thanks to Lensgrinder that point me to this calculator.
http://calculators.brent-mccardle.org/pow.html.
I will use this prescription and see what happens.
You are paying attention to every detail but you are trying to duplicate an Rx?
And you're an optometrist?
Something does not compute, senor.
Correct. I am a Optometrist. Partialy retired. But has spend time in the Lab. and dispensing because I believe that the patient did not came for a prescription but for a solution.
In my country a Optometrist can own stores and labs. There is no restriction.
I work for a family business and we own a chain of stores and a lab. Being retired is doing what you want to do and I spend now most of the time in the lab.
Going back to the presciption and the patient. We have no previous record of him. This is the first time he visit us.
He has excelent vision with his old lenses and the prescription from the exam is similar to the one I read on the lensmeter from his old lenses.
So. I want to make a lens as close to the old ones as possible and with the adition of IOT technology.
The prescription from the eye exam will not always be the most confortable for the patient.
Got it.
I caution against ordering the RX as you calculated. Just send your lab the prescribed RX and POW measurements.
The IOT FF calculator will do the rest and provide a compensated RX close to what you calculated using the program that lensgrinder referred you to. If you submit the RX as you calculated, the final compensated RX that you receive will be calculated against that, and not the actual prescribed RX. You, nor your patient, will like what you get back.
Also, as this RX is is along the 180, and not oblique, the subtle differences will not provide a 'wow' factor in overall vision. Your patient may experience a slightly better off axis vision and expanded field of vision. Then again, it may not be that noticeable. The only time a compensated SV will measurably outperform a standard toric SV is with oblique astigmatism and/or high curve/difficult to fit frame. I'm hoping that neither you, nor your patient is expecting a night and day difference.
Lensy, what say you about this?
Since this patient is -10.00 in the vertical meridian, what if he were a presbyope? Would you be more jazzed to expect an improvement on downgaze, vs. a traditional PAL?
Here's a boring anecdote: as a higher myope, when I switched to free-form PALs I was highly impressed with the near optics on downgaze. I'm sure there are a variety of factors, but is the "expansion of the field of vision" a likely factor?
I remember switching from crap 1990's SV poly to Spectralite ASV and feeling like I went to heaven.
Thanks for you post.
The job with prescription
-6.62 -2.95 × 180
-7.13 -3.22 × 180
Is about to be edged.
But Just in case and following your advice, I will run another calculation on Innovations with the prescription
OD -6.50 -2.75 x 180
OI -7.00 -3.00 x 180
And make a second pare of lenses.
Thanks.
Apples to peaches doc.
FF pals allow changes to the corridor length and width based on POW, and makes subtle adjustments to the add (even with avg POW) which was never possible in molded PALs. Remember, molded PALs are fixed, regardless of the standard or short version. Depending on the type of FF PAL, the compensation can soften the transition, giving you the illusion of a wider corridor, thus, improving the comfort of your downward gaze. Some newer designs even incorporate a digital device zone (somewhere between intermediate and near for smartphone users). But physics is physics, and will always be.
For prescription
-6.62 -2.95 × 180
-7.13 -3.22 × 180
IOT calculated
-6.36 -3.09 x 2
-6.86 -3.37 x 179
---------------------------
For
OD -6.50 -2.75 x 180
OI -7.00 -3.00 x 180
IOT calculated
-6.25 -2.89 x 2
-6.73 -3.15 x 178
On both. Panto=5 pano=9
If I'm reading this correctly, this Rx is now DOUBLE compensated which is counter productive. Also, I'd expect to see a small amount of Base In prism after compensating. Maybe edging has that covered?
Have I told you today how much I hate poly?
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