How can an 11 diopter myope see 20/25 without squinting?

Discussion in 'Optometry' started by drbizzaro, May 31, 2008.

  1. drbizzaro

    drbizzaro Varilux/Essilor Advocate

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    Just a question to the doctors out there who are good with optics and physiology:

    How is it possible for my 11 diopter patient to see 20/25 uncorrected without squinting? I mean, she functions fine without glasses. She has never had glasses and is currently 25 years old.

    Here are the exam findings:

    VAsc, OU: 20/25-2
    VAcc, OU: 20/20

    MR: OD: -11.00 DS
    OS: -11.00 DS

    RET: OD: -11.25 DS
    OS: -11.25 DS

    SLEX: WNL
    FUNDUS: posterior staphyloma OU

    Subjective comments: with corrective lenses, things are sharper, but not significantly sharper. Also, everything is more vivid and brighter. However, letter clarity is about the same as it was before.

    Can anyone explain this? I was careful to notice if the patient squinted at all. And there was no squinting what-so-ever. I tested VA with lights on and off. In outdoor environments and indoor.
     
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  3. KHE

    KHE Senior Member
    Optometrist SDN Advisor

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    She is either the world record holder for PRA or there is something way off with that refraction.
     
  4. drbizzaro

    drbizzaro Varilux/Essilor Advocate

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    That is what I was thinking. But I also had the other doctor do a quick recheck in case I missed anything. The other doctor found the same Rx.

    Also, autorefraction was within 0.50D of the -11.00 OU (after tropic was utilized for dilation)
     
  5. vsarge0708

    vsarge0708 Nova class of 2011

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    Wow, that's one hell of a depth of focus. How teeny tiny were her pupils--was your patient a prostitute?
     
  6. gochi

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    :eek:

    Are you kidding me!
     
  7. fonziefonz

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    I think he's referring to a possible STD related issue.

    Maybe she memorized the chart somehow?

    Or could be a crazy neurological issue.
     
  8. vsarge0708

    vsarge0708 Nova class of 2011

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    Yes and no, the magnitude of depth of field/focus is a function of pupil size--the smaller the pupil the larger the depth of field/focus [the caveat is that small pupil size increases diffractions]. There is syndrom called Argyll-Robertson's pupil in which the pupils are small and do not dilate well with atropine [the pupils also do not constrict when exposed to light, but constrict in the near triad constriction/convergence/accomodation]. A known etiology of this syndrome is neurosyphilis, hence its nickname "prostitute's pupils".
     
  9. gochi

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    Dang...thats alot of info.
     
  10. fonziefonz

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    If you're going to go to Opt school, get used to it! :rolleyes:
     
  11. Karnak

    Karnak Karnak

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    Dude that is one of the funniest things I've read all day
     
  12. eyepoker

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    Does this have similar idea as a pinhole test?

    I heard that if you use a pinhole probably, theoretically all the refractive errors can be corrected because the light would go through the hole in a straight line without bending ? so does having a small pupil have similar effects as having a pinhole test?
     
  13. vsarge0708

    vsarge0708 Nova class of 2011

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    Yeah sort of--a pinhole will increasing the depth of field/focus [about +/- 5 Diopters in the literature I've studied so far]. A pinhole probably won't "correct" all of the refractive error due to the decreased amount of illumination reaching the retina caused by having the pinhole infront of your face, as well as the diffraction effects of having such a small aperture. Having a small pupil will increase the depth of field/focus, but at a certain point the diffractions caused by having a smaller pupil will decrease visual acuity [If I remember correctly, I think going from a 3mm pupil to a 1mm pupil the diffractions increase exponentially, and going from 3mm to a 7+mm pupil the aberrations increase drastically, so 3mm was basically the best compromise between low aberrations and diffractions. I think the magic number for a pinhole is 1.2mm].
     
  14. Karnak

    Karnak Karnak

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    I think the pinhole explanations are missing something...
    Get any functional emmetrope to hold a +11.00DS in front of their eye, with a pinhole, and see how they go. Pinholes only get you so far...
     
  15. vsarge0708

    vsarge0708 Nova class of 2011

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    ...reread my last post
     

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