I have a doc specializing in pediatrics, and I'm playing catch up. Plenty of high power and MF scripts for pint-sized patients. I'm hoping some of you brilliant folks can point me in the direction of any statistical surveys of eyeball metrics (particularly axial length/center of rotation, etc.) that may be out there. If there's any literature on how reliably those vary by degree of refractive error, that'd be awesome and very appreciated as well.
Thank you in advance!
What do you need that information for? I don't know anything like that.
A quick Google search will provide a ton of sources. Just search for Multifocal for Children. In the old days, some kids with focus issues were fit with bifocals, primarily by ODs, who felt it would help decrease progression of myopia. Bifocals used were usually large, Executive's often preferred, and fit pupil center. Most MDs did not use this technique. Interestingly today, search for scholarly articles on Myopia Control. One quick example I saw immediately was this one:
ORIGINAL ARTICLES
Multifocal Contact Lens Myopia Control
Walline, Jeffrey J.*; Greiner, Katie L.†; McVey, M. Elizabeth‡; Jones-Jordan, Lisa A.§
Author Information Optometry and Vision Science 90(11):p 1207-1214, November 2013. | DOI: 10.1097/OPX.0000000000000036
Google and other search engines can help expeditiously. Lots of information available.
I hope this is helpful!
I'm in the habit of using "27" for center rotation in calculating NPD, without knowing standard deviation I trust it's still a far sight tighter than the infamous "drop 3." My last gig before sabbatical was with an Ophthalmology clinic's patient base with an average age of 60, so it's probably been over ten years since I've dispensed multifocals to kids. That stock "27" I found here on Optiboard in between then and now seems like an invitation to trouble now that I'm seeing these patients on a very frequent basis. With the smaller scale and consequently higher relative margin of error in fitting measurements, I want to find the best grip on QC I can get. For those kids ending up in PALs I'd really like to ferret out what working assumptions are in play in their design calculations and size up the risks, if any.Originally Posted by drk
I can already hear you thinking "why not just measure with the pupilometer?"For adults I've trusted the calculation from a Distance PD, preferring not to let that 0.5mm margin of error creep up in percentage to scale. But you're right, for kids a pupilometer measurement might be better than a careless calculation on my part. But then again, they're squirmy...and using the toggling-wink/PD stick trick on kids is very tricky to double-check the pupilometer because of the disparity of PDs between patient and optician. Nigh-impossible to double-check the pupilometer on a near setting as far as I'm aware.
(Don't forget to measure those hobbit-sized focal lengths, folks.)
Thank you kindly, Warren, I imagine it is very helpful to a different question--one I may very well have in the future! As fate would have it, I was aware of this study before I posted, but as you can see the metrics in the abstract aren't revealing any actual ocular measurements. While the p value advertised is certainly attention-getting and one would hope they're derived from objective measurements, I'm not sure even that would carry over to statistical validity for any inferences pertaining to my query about length measurements in the general population, including young hyperopes.
The source provided in a wiki article I found directly addressing raw ocular metrics was another pubmed paper, but that link seems to have gone missing. In these days of Replication Crisis in science publishing, that certainly gives me pause. You're right that search engines will likely be an unavoidable tool, but so far "a quick search" hasn't been fruitful and vetting the data will be considerably longer than finding it. I still think odds are good someone here is way in front of me on this and has some of this path cleared already.
So you're interested in calculating near pd on pediatric patients?
For segmented MF?
There is a thread here (I won't link it for obvious reasons) that gives near p.d. formula without center of rotation.
PALs don't need near p.d. but with a peds ophthalmology patient base you probably aren't going to do many of those. Just FT28's.
Hayde,
COR (eyes' Center Of Rotation) distance to the corneal plane/vertex averages 13.5mm. The average vertex distance to the spectacle plane is 13.5mm, for an average stop distance of 27mm. Brent from Zeiss (Lensgrinder here on OP) suggested this formula for adjusting the cornea vertex distance for refractive error-
COR 13.5mm - (0.2 x sphere equivalent)
I believe that's for hyperopes, CoR 13.5mm + (0.2 x sphere equivalent) for Myopes.
https://www.2020mag.com/ce/lens-design-and-the-eyes
https://onlinelibrary.wiley.com/doi/...1111/opo.12940
Best regards,
Robert Martellaro
Last edited by Robert Martellaro; 07-31-2023 at 11:44 AM.
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.
Again, countless sources available. Calculation of the near PD based on center of rotation of a developing eye is not necessary. Manual measurement will be the best option, measuring from canthus to canthus, not attempting to use a pupillometer. If you are describing "drop three" as a segment height, which has been common over time, that also has 0 to do with near PD Inset. A good source is Systems for Ophthalmic Dispensing.
You will note that there are many new spectacle multifocal lenses designed for myopic control specifically for children. See this article for further information. https://www.mykidsvision.org/knowled...myopia-control
A study related to metrics in China: The accuracy of the axial length and axial length/corneal radius ratio for myopia assessment among Chinese children
https://www.frontiersin.org/articles/10.3389/fped.2022.859944/full
I hope this is helpful.
Thank you, gentlemen!
I will be pouring over this just as soon as back-to-school season is over!
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