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Thread: Refraction distance standards

  1. #1
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    Refraction distance standards

    Hello all,

    Why is refraction distance not a standard measurement listed on Rx's in the US? With the increasing use of compensated lens designs that rely on position of wear measurements why are refraction distances not more commonly recorded, or shared by optometrists? Without knowing the refraction distance, how can we accurately calculate vertex distance and lens tilt/wrap compensations? I would think especially for those high power >+/-10.0D wearers it would be a given for better optics, and more closely align with the intended optical correction. Without how do we really know if something is within ANSI tolerance? It could be in tolerance of 13mm, but what about 10mm?

    The point being, accurate measurements give accurate results, and if the measurements we use are averages or standards, the lenses will be just that. I realize that refractions can be subjective, in that phoropter distance can vary, pupil sizes differ, responses can vary by person, and diopters are prescribed in 0.25 increments, but with current technology shouldn't we strive for more precision, and less subjectivity?

  2. #2
    What's up? drk's Avatar
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    Yes, we should at certain power levels.

    Problem is that refracting distance is difficult to measure in the exam room. I blame the phoroptor companies.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Agreed that refractive vertex does need to be standardized. As for removing subjectivity? Good luck with that. 1 or 2 can, and is difficult for most. Comfort? Sharpness? What about blood sugar? AM refraction vs PM refraction come into play here, as well.

    What would help is for fitters to keep the 13mm average in mind when selecting the proper frame fit. ODs would thank you for this, as will the dispensary and the patients. Less redos=more profits.
    I bend light. That is what I do.

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    Quote Originally Posted by lensmanmd View Post
    Agreed that refractive vertex does need to be standardized. As for removing subjectivity? Good luck with that. 1 or 2 can, and is difficult for most. Comfort? Sharpness? What about blood sugar? AM refraction vs PM refraction come into play here, as well.

    What would help is for fitters to keep the 13mm average in mind when selecting the proper frame fit. ODs would thank you for this, as will the dispensary and the patients. Less redos=more profits.
    The point was with as subjective as refractions are, we should aim to reduce the variables that we can control. And saying it’s on fitters to keep the 13mm average in mind is exactly the problem. Even if a fitter assumes 13mm was intended, if it wasn’t then with vertexing it can throw the lenses off tolerance after a certain power threshold let’s say roughly +/-6. It doesn’t need to be a standard distance, but a standard to give the distance used.

    A counter point being not all ODs use 13mm refractive distances, using sighting prisms and measuring refractive vertex isn’t hard, and takes the guess work out of the equation. Fitters would thank you for this. The more accurately we can fit, fabricate, and dispense a pair of glasses to the prescribed power the better. Less redos = more profits.

    beyond all of that, by specifying the distance it clarifies if considerations were taken for asymmetrical facial structures when the Rx was prescribed. I.E. the angles of the patients face if the optics are not equidistant from the eyes, recessed globes, a protuberant frontal bone, all can change the refractive distance.

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    In the UK the tested vertex distance must be given on all powers over 5.00 (in any meridian). It takes 2 seconds and makes dispensing accurate. No use having all these fancy lenses if your measurements are wrong!

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    Eyes eastward... Uilleann's Avatar
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    I'm guessing 95% of dispensers today (and possibly ODs/MDs) wouldn't know how to use a distometer if it jumped up and bit them...

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    What's up? drk's Avatar
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    We need better distometers. I don't have one but that prism-doubling kind would be great.
    However, again, phoroptors have crap for vertex control, so...it's moot.

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    Quote Originally Posted by Uilleann View Post
    I'm guessing 95% of dispensers today (and possibly ODs/MDs) wouldn't know how to use a distometer if it jumped up and bit them...
    I've never used one, not a surprise when I worked for the evil empire for quite awhile and now I'm at a private office. But I think its pretty simple right? Have the customer put the glasses on and have them close their eye and measure from eye to backside of the blank in the frame. I guess I would be confused on how much (if any) do you would add for thicker Rxs and do you always assume a 50/50 bevel?

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    OptiBoard Professional KrystleClear's Avatar
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    I agree. I would also really love for best corrected visual acuity to be on scripts too. It's no big deal if it's a patient seen by our docs, because I can just look at the EMR notes, but for outside RXs I have no way of knowing what is going on medically with the person's eyes and whether or not the refraction even got them to 20/20. Helpful especially for older patients who forget they have visually limiting eye diseases, which we encounter often, unfortunately. But, I know in our office, asking the prescribing doctors to add more onto the scripts won't go over well. Our MD has so many problems using the EMR software as it is, even if it is only a few more clicks.
    Krystle

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    Quote Originally Posted by KrystleClear View Post
    I agree. I would also really love for best corrected visual acuity to be on scripts too. It's no big deal if it's a patient seen by our docs, because I can just look at the EMR notes, but for outside RXs I have no way of knowing what is going on medically with the person's eyes and whether or not the refraction even got them to 20/20. Helpful especially for older patients who forget they have visually limiting eye diseases, which we encounter often, unfortunately. But, I know in our office, asking the prescribing doctors to add more onto the scripts won't go over well. Our MD has so many problems using the EMR software as it is, even if it is only a few more clicks.
    100%!! Well said, I wish this was a standard.

    Knowing if a person can even be corrected back to 20/20 is super helpful when someone experiences a problem with their new glasses. I try and look at that when I am selling to them so I can set the expectations before and then remind them when they pick them up if they are having issues. I see it a lot with people who have cataracts, "until you get your cataracts out this is kind of the new normal, it is as good as the doctor could correct you to." Or with diabetics, they see better at certain times of the day, I check what they told the Doc their A1C was.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Quote Originally Posted by NAICITPO View Post
    I've never used one, not a surprise when I worked for the evil empire for quite awhile and now I'm at a private office. But I think its pretty simple right? Have the customer put the glasses on and have them close their eye and measure from eye to backside of the blank in the frame. I guess I would be confused on how much (if any) do you would add for thicker Rxs and do you always assume a 50/50 bevel?
    Never assume anything. Let’s say a sun frame, polarized lens. Front bevel. Happens to be a 6 base form. RX is -10. Then, a dress pair. 4 base form. 40/60 hide a bevel. Measure vertex accordingly, but assume that the sun is on a 2bc, and the dress is .5bc. Now, the lab will determine the best fit regardless of your vertex when edging. There goes your vertex. Then, imagine the converse for a + 10.
    Provide panto and wrap/panoramic. Let the FF calculator do its thing from there, providing that your lab utilizes Z data.
    I bend light. That is what I do.

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    Quote Originally Posted by lensmanmd View Post
    Never assume anything. Lets say a sun frame, polarized lens. Front bevel. Happens to be a 6 base form. RX is -10. Then, a dress pair. 4 base form. 40/60 hide a bevel. Measure vertex accordingly, but assume that the sun is on a 2bc, and the dress is .5bc. Now, the lab will determine the best fit regardless of your vertex when edging. There goes your vertex. Then, imagine the converse for a + 10.
    Provide panto and wrap/panoramic. Let the FF calculator do its thing from there, providing that your lab utilizes Z data.
    So if I choose a progressive style that has PoW measurements, does the lab automatically adjust them based on what the lab determines is the best fit?

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    For average POW RXs, vertex is the least effect measurement. Instead, panoramic angle/wrap/frame form and panto are more effective.
    Most RXs that would benefit from FF are generally out of range for FF anyway.

    That said, knowing the refractive vertex can go a long way in assisting the fitter in choosing the correct frame fit and adjusting final RX for high RXS.
    I bend light. That is what I do.

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    Some thoughts…
    If the refraction incorporates a usual amount of pantoscopic tilt and wrap degree, we should minimize the major errors from refraction to fit errors. As I’m not trained in refractions I’ll have to differ as to whether this can be done effectively. A usual 50mm frame will fit very close to the phoropter fitting and corresponding powers to standard base curve selection will result in very little vertex errors. Remember we need powers more than 10 diopters with a 2 mm vertex fitting error to even start exceeding ANSI standards for power.
    If you want to use your distometer the average inside curve for glazed frames is around 3.5 diopter, so powers needing 2 to 8 diopter base curves won’t result in large errors in 94% of the population.
    As lensmanm pointed out… when we get silly with powers, base curves, bevel positions and extreme lens sizes to satisfy cosmetic needs all bets are off. At this point you almost have to make the glasses to measure the error(s). Also, with the advent of IOL for cataracts the pseudophakia lens and errors associated with them are a thing of the past. Contact lenses can also be our friends in minimizing said problems.
    There was a time when frames were made with adjustable guard and arms a skilled optician could make some vertex adjustments. (Full discloser, I never could make these work).

    Chris

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    What's up? drk's Avatar
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    Not only do phoroptor heads NOT have faceform (they're flat), when converged for near testing, they have negative face form!

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    Master OptiBoarder CCGREEN's Avatar
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    So how many ways are we going to split this hair of micro measurements for powers lens designs and vertex distance and wrap ect ect ect.
    If you remember one of the biggest complaints we get from a patient is, "My glasses just wont stay in place. They slip down my nose....."
    What is the point of all those wonderful measurements and designs if the glasses are going to slide 3mm which will jack up all the detail work you just did?
    Sure fitting the frame properly is very important but most people do not take the time to do that. Doing it would assure that the detail you have been working for would be achieved.

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    Quote Originally Posted by CCGREEN View Post
    So how many ways are we going to split this hair of micro measurements for powers lens designs and vertex distance and wrap ect ect ect.
    If you remember one of the biggest complaints we get from a patient is, "My glasses just wont stay in place. They slip down my nose....."
    What is the point of all those wonderful measurements and designs if the glasses are going to slide 3mm which will jack up all the detail work you just did?
    Sure fitting the frame properly is very important but most people do not take the time to do that. Doing it would assure that the detail you have been working for would be achieved.
    Well yes, if you are saying we should properly fit the expensive PoW progressive we just sold then you are correct. I think your point is there is some diminishing returns for all the measurements. Especially if people either don't take care of their glasses (I swear I DON'T KNOW WHAT HAPPENED!?! They just bent themselves???) or we don't take the time to make sure they are properly fitted. But that is no reason to not try and be as accurate as possible when we have the ability to do so. You are increasing the best vision possible even if your customer doesn't always get that, it is still a good thing.

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