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Thread: Vertex distance & population statitstics

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    Vertex distance & population statitstics

    Is anyone aware of any studies on vertex distances measured at the phoropter?

    I most often read 13 or 14. ODs I know personally reflexively say the 'average' is 12 or 12.5. In either case, I find that supremely unhelpful absent a measure of standard deviation, not to mention subsets by race and gender and perhaps even age. Most of the patients I end up measuring in the dispensary have two different monocular values.

    Do docs have some study citation for this? Or is this just a hand-waving rumor that travels between them with far more confidence than it deserves?

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    Master OptiBoarder rbaker's Avatar
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    Much ado about nothing.

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    Quote Originally Posted by rbaker View Post
    Much ado about nothing.
    I'll happily take some clinical studies that support that conclusion as well.

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    Blue Jumper I'll happily take some clinical studies that support that conclusion.................

    Quote Originally Posted by Hayde View Post

    I'll happily take some clinical studies that support that conclusion as well.

    That is totally full of good intentions to be perfect.

    However when you look at the population wearing glasses halfway down their nose, and also crooked on their face, by either bad adjustment or mistreatment, it will not really matter as a fact.

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    I have no illusions of perfect, and I'm not concerned about the vast majority of powers 5D & under. However, on days when the powers are 7+ (or today for me, 9.25,) we live in a world where people are paying for digital options where order increments are at the 1/8th. What exactly are we selling and charging for if it's "much ado about nothing?" I have a Px who's no worse than a 6D, but wears his PALs halfway down his nose. If I'm not paying attention to vertex, he's back in the clinic for a 'spec check.' An avoidable one...

    And especially when they're not and I have to pick a quarter, Px buys 3 pairs. I know what to do with the 12 metal and the 9 zyl. The 11...? Not everyone has convenient noses to fudge vertex, especially on thick minus lenses.

    I'm not trying to estimate my Px based on statistical averages. I do need to make a point that seems like it'll do some good here too. My hypothesis is that "'12' and a handwave" doesn't cut it.

    Who's ready to prove me wrong?

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    Well, 12 is supposed to be the standard. Some ODs will actually write the refracted distance on higher RXs (yes, gasp!)

    My old life as a dispensing optician, I did actually tweak the submitted RX based on the frame fit (before the rise of Freeform) A pain, but it worked. The manually compensated RX that I provided on the worksheet gave my patients the RX that they needed.

    With freeform, the opticians' job is made easier by giving the lab the vertex distance and letting LMS calculate the compensated RX for you. The catch is with toric surfacing. This is when the formulas that we tried to memorize for the ABO came in to use Dc=D1/(1+d x D1)

    I would rather steer the patient over to freeform and provide the POW to make sure that my patient gets the RX they need.

    Not proving you wrong. I wish all ODs and MDs would write the refracted vertex along with the RX, but that my be asking way too much. It's just that we, as opticians, need to work our magic with numbers.

    My part, as a Lab Manager, is wishing that my opticians would provide me with the necessary vertex distance for higher RXs, so that I could provide them with a more accurate perceived RX. Our FF range is -10D, max, so I need to employ toric surfacing on anything higher.

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    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Hayde View Post
    Is anyone aware of any studies on vertex distances measured at the phoropter?

    I most often read 13 or 14. ODs I know personally reflexively say the 'average' is 12 or 12.5. In either case, I find that supremely unhelpful absent a measure of standard deviation, not to mention subsets by race and gender and perhaps even age. Most of the patients I end up measuring in the dispensary have two different monocular values.

    Do docs have some study citation for this? Or is this just a hand-waving rumor that travels between them with far more confidence than it deserves?
    Brooks and Borish (ophtho disp.) say the average is 14mm, Rubin (optics for clinicians) says 15mm.

    The distance from the lens in the refractor head to the corneal plane might be more than anticipated.

    https://www.ncbi.nlm.nih.gov/pubmed/12160154

    From my experience, the doctor's and wearer's vertex distance are usually close in value due to orbital features, assuming that the phoropter and frame are positioned as close as possible to the eyes.

    Hope this helps,

    Robert Martellaro
    Last edited by Robert Martellaro; 08-28-2017 at 07:21 PM.
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    I know this thread is more than a week old, but I would just like to throw in my two cents.

    We send a good bit of our work to Digital Eye Lab. They say that average refracted vertex distance is 13mm. For the most part we have had success with that, unless the doctor specifically states that the VD is something else.
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    I'm fairly certain in school we were told 14mm, which seems far. For the most part, if the patient has a high Rx, I trial frame it and try to over-refract at about 13mm. There's probably more variability in the phoropter than expected. Many people with long lashes stay back and many people like to cram their face tight. But yeah, for the vast majority of people, vertex distance at the phoropter isn't a concern.

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