Toric lens and accomodation

Discussion in 'Optometry Archives' started by Gary, Jun 14, 2006.

  1. Gary

    Gary Guest

    A quick query, anyone know if while wearing a toric lens, does it alter the
    eyes accomodation abilities?

    TIA
    Gary
     
    Gary, Jun 14, 2006
    #1
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  2. Gary

    Neil Brooks Guest

    I'm not an eye doctor, but ... I do wear toric lenses.

    My first question would be "Why?" It seems like you're experiencing
    something, and you're trying to understand what's causing it. If so,
    perhaps you should elaborate.

    What's the issue you're having?

    What's your prescription?

    What's your age?

    These might lead you to a better answer....

    Neil
     
    Neil Brooks, Jun 14, 2006
    #2
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  3. Gary

    tkopan1 Guest

    Yes, you will accomodate. If you are myopic and remove your glasses to
    read, you are not accomodating fully. After Wearing a corrected
    contact lens prescription, you should begin to accomodate normally
    again. The same applies to lasik. If you are hyperopic (farsighted),
    your are accomodating too much already. A corrected toric lens will
    have you accomodate less.

    -Dr. Tom
     
    tkopan1, Jun 14, 2006
    #3
  4. Gary

    Gary Guest

    The reason I ask is that I'm presbyopic and my close focussing abilities
    vary between wearing contact lenses and glasses. It's better with the
    latter.

    I've assumed this is purely because of the physical distance from the eye
    when being corrected by glasses. Or does/can a toric contact lens constrict
    the eye's accomodation abilities?

    Regards
    Gary
     
    Gary, Jun 14, 2006
    #4
  5. Gary

    Neil Brooks Guest

    Contact lenses REDUCE the amount of accommodation that a FARSIGHTED
    person needs. They INCREASE the amount of accommodation that a
    NEARSIGHTED person needs.

    It *could* be just what you alluded to below (known as the "vertex
    distance"). IF the vertex distance wasn't factored in appropriately
    when either or both your glasses or contact lenses were made, then you
    would effectively have different prescriptions.

    If that's the case, you really *don't* have an apples-to-apples
    comparison between specs and contacts.

    You might want to get back with your optometrist to see if your
    contacts need the prescription tweaked. Depending on your Rx, it
    could be that you're due for reading glasses *over* the contacts.

    Hopefully, one of the docs can sweep up behind me if need be ;-)
     
    Neil Brooks, Jun 14, 2006
    #5
  6. I thought it was the opposite, Highly myopic individuals need to accomodate
    slightly more with their contact lenses and vice versa when presbyopic.

    Base in prism when reading with spectacles also help.

    Roland Izaac
     
    Philip D Izaac, Jun 15, 2006
    #6
  7. Gary

    Dom Guest

    The short answer is "no". If you're experiencing difficulty with close
    focussing while wearing a toric lens it could be due to the lens being a
    slightly different strength to your glasses or various other factors. In
    my opinion the difference in convergence required between specs and
    contact lenses isn't really significant but I know that others disagree.

    Dom
     
    Dom, Jun 15, 2006
    #7
  8. I think you guys are comparing apples to oranges.

    Myopes have to accommodate more in full distance Rx glasses than they do
    in full distance Rx contacts, although certainly less when not wearing
    any correction.

    Hyperopes have to accommodate less in their full distance Rx glasses
    than they do in full distance Rx contacts, although certainly more when
    not wearing any correction.

    Now is that perfectly clear?

    w.stacy, o.d.
     
    William Stacy, Jun 15, 2006
    #8
  9. Gary

    Neil Brooks Guest

    As mud ;-)

    I can't find the two original cites that I used to post, but ...
    here's a quote and the cite from which I pulled it:

    "The accommodative demand on hyperopic patients is less with contact
    lenses than with spectacle lenses, and so they are more readily
    accepted"

    FROM:
    Fitting youngsters with contact lenses
    From children to teenagers

    http://www.optometry.co.uk/files/16b584a2c9ab1d496644a3d8e3b2184c_bansai20040924.pdf

    OR: http://tinyurl.com/mxxsf

    Interesting, and only tangentially related is:

    http://aglasser.opt.uh.edu/publications/KV&G2003.pdf

    I also found this:

    "In this respect, it is interesting that wearers of glasses
    accommodate less and have lower convergence demands than emmetropes or
    wearers of contact lenses due to optical reasons" [presumably implying
    the prism effect of the spectacle lenses, BUT ... CL's (primarily
    RGP's) have this, too, no??]

    FROM: http://www.agingeye.net/myopia/3.2.1.2.php

    Which seems to cite this:

    http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1175259&blobtype=pdf

    OR: http://tinyurl.com/zj67f

    Now THIS should clear it right up ;-)
     
    Neil Brooks, Jun 15, 2006
    #9
  10. Gary

    Neil Brooks Guest

    I *think* I'm following you, Robert, and/but I'm very much intrigued.
    When you speak of the vergence, or prismatic effect, even of a thin
    lens, how is it calculated whether the prismatic effect is BI or BO?

    Is it purely a function of whether the lens is minus or plus?? If so,
    then is *that* the basis for the delta in accommodative demand
    introduced by spectacles as different between myopes and hyperopes?

    I'm curious because--if I DO understand you correctly, and--for
    example--my spectacles (which do NOT have "added" prism correction)
    INDUCE prism that is the *opposite* of what I need (inducing BO, for
    example, when I'm exotropic), then I would need to force additional
    accommodation simply to compensate for the inherent prismatic effect
    of the thin lens, no?

    Do I have that right?

    If so, and if it is such a readily quantifiable issue, then
    couldn't/shouldn't compensatory prism be introduced in spectacle
    lenses--particularly higher power--to offset this effect and minimize
    "spurious accommodative load?"

    Thanks much, Robert.
     
    Neil Brooks, Jun 15, 2006
    #10
  11. Gary

    Dick Adams Guest

    You're all nuts!

    Any eye corrected to focus infinity unaccommodated will need to
    accommodate 2 diopters to focus text at 0.5 meter, etc.

    "Toric" does not change anything, except for being another one
    of your misty concepts.
     
    Dick Adams, Jun 15, 2006
    #11
  12. Gary

    Neil Brooks Guest

    The topic shifted. You simply didn't keep up.

    The topic shifted into the relative accommodative demand induced by:

    Glasses in hyperopes;
    Glasses in myopes;
    Contact lenses in hyperopes;
    Contact lenses in myopes.
     
    Neil Brooks, Jun 15, 2006
    #12
  13. Neil Brooks wrote:

    I think Robert was using the term vergence to describe spherical
    refractive power as opposed to prismatic effects. The term is confusing
    because convergence can mean light focused by a plus lens, and it can
    also mean turning the eyes inward (binocularly).

    At any rate, you can tell if prismatic effect is base in or out by
    looking at the profile of the lens. If it is a plus lens and you are
    converging binocularly toward a near object, you are looking through
    base out prism (the centers of your lenses are thick, the nasal edge is
    thin, so your induced prism is base out). Just the opposite for minus.
    Plano lenses have zero prism induced, no matter where you look.

    Nope. That effect is due to the differences in effective powers of plus
    and minus lenses that are placed a finite distance from the eye, e.g.
    spectacle lenses.
    If your lenses are plus, and you converge toward something near, you
    indeed get a certain amount of base out prism. But if you added
    compensatory prism for this, it would give you more base in prism in the
    primary position, something you might or might not want.
    If you are exo, you might indeed want some base in prism. The effect of
    converging to a near object means that whatever base in prism you have,
    it will be effectively less and less as you bring the object nearer and
    nearer. Again, I don't think it has much to do with accommodation.

    w.stacy, o.d.
     
    William Stacy, Jun 15, 2006
    #13
  14. Gary

    Dick Adams Guest

    Yeah, well, I really got messed up by that relative accommodative demand
    inducement shift.

    You are really getting the hang of this stuff, Neil Brooks! Have you ever
    considered going to Professional School? Maybe you could rise to do
    something important in the interest of mankind, like writing
    speeches for the President, for instance.
     
    Dick Adams, Jun 15, 2006
    #14
  15. Gary

    Neil Brooks Guest

    Thanks, Doc.

    Interesting ... and ... good stuff.

    I would have to think, though, that virtually any unintended/unwanted
    intervention into the near vision triad should have some impact on
    accommodation, no? Whether it's undercorrecting a hyperope for
    reading to ease CI or adding plus to a near-point esophore...

    Aren't these strategic interferences with the near vision triad to
    "strike the balance?"

    I my case (always eso-, but exo- 8yrs post-op), that inherent BO prism
    in a high-plus lens might just *be* a bad thing.

    Might be something for others with strong Rx's and/or alignment issues
    to consider. From what you're saying, it would *seem* that ... to be
    *really* properly corrected for a phoria/tropia ... the practitioner
    would have to add the combination of the findings from the prism bar
    exam AND the prism inherent in a stronger spectacle lens.

    I'm guessing that this latter could easily amount to several diopters,
    no?

    Thanks again.
     
    Neil Brooks, Jun 16, 2006
    #15
  16. Gary

    Neil Brooks Guest

    Thanks again, Robert, but ... maybe only in my case (accommodative and
    binocular dysfunction) ... wouldn't one--out of an abundance of
    caution ... want to factor in the inherent BO prism in a strong plus
    lens?

    I seem to be a good 10-12d exo- at near now (by measurement over the
    contact lenses). I would imagine that prescribing 12d of BI prism in
    reading glasses (no cl's) might *undercorrect* the exo- exactly
    because of what you describe above then, no? If so (as I referenced
    in my post to Bill Stacy), then would(n't) it be prudent to factor in
    this inherent prismatic effect when prescribing (at least in a case
    like mine)?

    Realistically, I'm thinking that ... since we're likely talking about
    people with a high degree of hyper/myopia ... then even IF there are
    (as you say) no vergence disorders present ... this sounds like a
    rather non-productive amount of "risk" with the only reward being
    slightly thinner lenses (that can--as *you* surely know) be mitigated
    with appropriate choice of materials.

    I feel like this is another "vertex distance" issue in higher powers
    and vergence issues: something that may not get factored into the
    equation consistently and accurately, but something that could
    dramatically impact outcomes.

    Follow?

    Thanks again.
     
    Neil Brooks, Jun 16, 2006
    #16
  17. Well sure, but that's just straightforward math: if you add plus at
    near, accommodation is relaxed by exactly the amount of the addition,
    and vice versa, assuming there is accommodation (phakic eyes under 55
    years old or so).

    Agreed, and it is correctable as Robert pointed out.
    Assuming you mean prism diopters, it's dependent on Prentice rule as
    Robert pointed out, easily calculable from power and decentration.
    Unfortunately, you can't easily do different p.d.s for distance and near
    in one lens.

    w.stacy, o.d.
     
    William Stacy, Jun 16, 2006
    #17
  18. Gary

    Neil Brooks Guest

    I just need to be sure that this piece wasn't overlooked in my case,
    and ... to raise it, generally, for other outliers like myself ;-)

    The glasses that I wear for distance ... when I'm NOT in cl's ... IIRC
    don't have any added prism. At my Rx, though, they may be imparting a
    fair bit of BO ... unintentionally ... and detrimentally.

    The last thing *I* need is to be exo-. If this issue is a
    contributing factor, I'll simply want to raise it with my ophth.

    For my particular case, this *could--* at least in part--explain why I
    seem to fatigue much more quickly with my glasses than with cl's.

    You know ... despite our buddy, Otis constantly posting things like

    "It is not hard to be "smarter" than a
    man who only requires 2 months of FUNCTIONAL
    training to put a kid into an excessive minus."

    .... you guys really have to juggle an amazing number of parameters ...
    all delicately balanced (and the associated geometry, math, and
    physics) ... to achieve optimal outcomes.

    I'm starting to wonder if ... maybe ... Otis isn't wrong after all ;-)

    Thanks again.
     
    Neil Brooks, Jun 16, 2006
    #18
  19. You can avoid that by having a pair made up with the optical centers set
    to match your monocular p.d.s at near. However, this will induce a fair
    amount of base in prism when you are looking at far objects through
    them, which if you are exo may not bother you. But another problem with
    unwanted prism is chromatic aberration. For this reason you might want
    to split the difference and set the o.c.s between your distance and near
    mono p.d.s.

    w.stacy, o.d.
     
    William Stacy, Jun 16, 2006
    #19
  20. I disagree with you William.

    Myopes do not accomodate more in full distance Rx glasses when compared to full distance Rx contacts. The fact is they accomodate less, the higher the Rx, the greater the vertex distance, the lower the accomodative demand. Therefore Myopes when wearing glasses accomodate the least, even less then emetropes. Hyperopes are just the opposite.

    So OTIS, please understand what I am saying here, The bases for your theories is wrong. And by the way, how are objects brought closer when the minus lens brings distant objects to focus at the patients far point, not any closer. Do you understand that at this far point the patient does not need to accomodate.

    I am expecting a rebutal from you Otis, Oh wow, I'm kidding myself, Otis never answers.

    Previous Post:"I thought it was the opposite, Highly myopic individuals need to accomodate
    slightly more with their contact lenses and vice versa when presbyopic"

    CORRECTION TO PREVIOUS POST.
    I meant to say hyperopic, not presbyopic.
    I appologise for the confusion.


    Philip D Izaac wrote:


    I thought it was the opposite, Highly myopic individuals need to accomodate
    slightly more with their contact lenses and vice versa when presbyopic.

    Base in prism when reading with spectacles also help.

    Roland Izaac


    I think you guys are comparing apples to oranges.

    Myopes have to accommodate more in full distance Rx glasses than they do in full distance Rx contacts, although certainly less when not wearing any correction.

    Hyperopes have to accommodate less in their full distance Rx glasses than they do in full distance Rx contacts, although certainly more when not wearing any correction.

    Now is that perfectly clear?

    w.stacy, o.d.
     
    Philip D Izaac, Jun 17, 2006
    #20
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