Adaptation to multi-focal contact lenses

Discussion in 'Contact Lenses' started by Pauli Soininen, Aug 24, 2005.

  1. What is the adaptation to aspheric multi-focal contact lenses based on?

    This is just a random site found with Google:

    The video shows how refractive power is divided in the lens. How can a
    person see only through one portion at a time?
    Pauli Soininen, Aug 24, 2005
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  2. Pauli Soininen

    RM Guest

    A person cannot see through one portion of a multifocal contact lens at a
    time (unless they are tangent streak gas perms). The vision is
    simultaneous-- i.e. some light is focused at distance while some is focused
    at near. The resultant image is "somewhat" clear at distant and near with
    peripheral blurring or ghosting. Some people can adapt to the resulting
    image while others cannot.

    In my experience, if the patient's expectations are managed appropriately,
    and a little chair time is expended by the doctor and patient working
    together to get the best correction possible, most patients are satisfied.

    The most important part is not to expect perfect distant and near vision--
    expect "good enough" acuity to accomplish everyday tasks.

    RM, Aug 25, 2005
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  3. Pauli Soininen

    The Real Bev Guest

    When I was trying multifocal RGPs some of them DID provide perfect distant and
    near vision -- but only for 1 second out of 60 (against-the-rule astigmatism,
    apparently). Crying shame, because it was like having real eyes again :-(
    The Real Bev, Aug 25, 2005
  4. Pauli Soininen

    Martin Guest

    I guess it is a variation on the mono-vision theme - the brain is remarkably
    good at learning to ignore things it does not want to see... As I posted in
    another message on this group, I am part way through a trial of Bausch&Lomb
    multi-focals and I am very pleased with them. I am moderately long sighted
    and need a +1 add reading glasses for any significant period of close work.
    From the minute I put the B&Ls in I had adequate vision at all distances.
    For the first half hour or so, if I analysed what I was seeing objectively
    there was something "strange" about it - not really possible to pin it down
    and not unacceptable. Now, I simply do not notice it - my distance vision is
    probably slightly better than I was getting with varifocal glasses, my
    close-up vision is about the same as with varifocals. I suspect that
    middle-distance vision (i.e. around ten to fifteen feet) is slightly worse,
    though that is subjective and it is still acceptable - the television does
    not seem quite as sharp as it does with glasses.

    As others have said, it is probably very dependent on expectations - if my
    son who is thirty years younger than me and has 20-20 vision without glasses
    saw the world the way I am, I dare say he would complain. For me, following
    years of living with varifocals or carrying round two pairs of glasses all
    the time, this is wonderful - I have more than adequate vision at all
    distances without anything hanging on my face! It is probably also dependent
    on your prescription - I am moderately long sighted with just a +1 add - not
    too much... Other people's experience could be very different, but it is not
    particularly expensive to find out.

    Martin Bradford
    Martin, Aug 25, 2005
  5. When I was trying multifocal RGPs some of them DID provide perfect
    I'm not sure what you mean. Do you mean that you could adapt to the
    uncorrected astigmatism momentarily or what?

    By perfect distant and near vision do you mean 100% unblurred, absolutely
    flawless vision in both sunshine and darkness, no halos?
    Pauli Soininen, Aug 28, 2005
  6. I have fit some version of multi-focal contact lenses for 25 years, and
    this is truly a golden age for the multifocal lens.
    The Bausch & Lomb can be "stunted" a little by putting a "low add" on
    your dominant eye and a "high add" on your non-dominant eye, and you
    get a "modified monovision" that relies on simultaneous perception at
    times, but allows great binocular fusion. In the hands of a skilled
    optometrist who loves to "play" with lenses, these products can let a
    good 90%+ of soft lens bifocal candidates be successful. Contrarily, a
    "cookbook" optometrist who reads the fitting guide and doesn't go
    "off-label" in his thinking might hit 50% success on his best day.
    doctor_my_eye, Aug 29, 2005
  7. Pauli Soininen

    LarryDoc Guest

    I've been reading this thread with interest and now I'll add my
    comments. I have a great deal of experience in fitting aspheric
    multifocal RGP and soft lenses. I wear them myself, mostly RGPs as they
    provide, for me, outstanding vision.

    Generalized statement about performance are not at all useful. I have
    some patients who do indeed achieve uncompromisingly excellent vision at
    all distances. (Definition: distance and near acuity equal to or better
    than that achieved with spectacle lenses, no "ghost/halo" at distance
    under any conditions.) I myself am in that group. Most of my patients
    do not achieve that degree of quality of vision as there are some
    optical compromises, but most achieve excellent distance and
    intermediate vision and good to excellent near vision. (Definition: as
    above, nearest near point of 20/20 vision equal to at least 20cm, which
    may not be close enough for some people's needs.) Some people
    experience some degree of "ghosts/halos" in reduced lighting at distance
    which does not impact near acuity at all but may reduce distance visual
    quality somewhat and generally be a little annoying. This is far more
    common in soft lenses than RGP.

    There are many optical and eye structural issues that affect what the
    wearer's optical experience will be. In my practice, I'd estimate that
    80% are completely satisfied, 15% live with less than optimum vision but
    are still quite pleased and 5% do not stay with the lenses for either
    comfort or optical reasons. With RGPs and carefully selected patients,
    the issue is more often comfort than optics.

    For soft multifocals, the " I think these are great!" numbers are much
    lower, with less than 50% achieving a visual experience approaching RGPs
    but 70-80% being quite satisfied. The "I give ups" are in the 20-30%
    range. Still, many people enjoy the freedom from multiple pairs of
    spectacles or the hassles of hanging readers around their necks or
    stuffed in their pockets and purses. With careful patient selection and
    doctor experience, soft multifocals are an excellent option for the
    "over 40's" group. And they're getting better all the time.

    I believe (hope, dream, loose sleep over it) that when they arrive,
    silicone hydrogel multifocals, due to their more stable/stiff
    construction may be much better. In theory, it can be done. They will
    need to come in a few different optic zone diameters and toric
    (astigmatism correcting) powers.

    I've found a very effective optical correction for folks with low add
    needs ( like up to 1 or 1.25 D) who have less than .5D astigmatism is
    plain old Focus Night&Day/Optix or Purevision lenses, which are somewhat
    aspheric by design. The experience can be enhanced by .25 more plus
    power in the near-dominant eye. Very, very little compromise there.

    --LB. O.D.
    LarryDoc, Aug 29, 2005
  8. Did you really mean 20 cm, or should that be 20 inches?

    w.stacy, o.d.
    William Stacy, Aug 29, 2005
  9. Thanks for the post.

    At low illumination, when the pupil is large, the rays have to enter the
    retina at multiple focals, don't they. So, a probable case is something like
    50% of the rays are passing refractive power A and 50% are passing power B
    (if it's bifocal and transition is not considered). The rays A and B are
    hitting the retina in at slightly different angle.

    You said that many patients experience no ghost/halo whatsoever. Do you have
    an explanation or what is your best guess, how exactly is this possible?

    Is there a difference between typically spherically aberrated (ex-myopic)
    laser operated eyes and myopic eyes with multi-focal contact lenses? Putting
    together 1 + 1 (if the portions are as shown in the video I posted the link
    to), both cases have near vision at peripheral cornea and distance vision in
    the center of cornea.
    Pauli Soininen, Aug 29, 2005
  10. They can't, except for translating (true) bifocals. All others result
    in out of focus paraxial rays. The "adapatation" that occcurs is some
    peoples' ability to ignore the blur.

    w.stacy, o.d.
    William Stacy, Aug 29, 2005
  11. Pauli Soininen

    LarryDoc Guest

    Whoops! Thanks, doc.

    LarryDoc, Aug 29, 2005
  12. The "adapatation" that occcurs is some
    Not noticing the blur in certain circumstances is a different thing than
    noticing the absence of any blur at all (as halos around lamps for example).
    According to LarryDoc:
    In my opinion it's impossible to not see a halo around a lamp unless the
    halo really is very vague, but, that can not the case if 50% of the rays are
    contributing to the halo. Unless there is something blocking those rays.
    Pauli Soininen, Aug 29, 2005
  13. That may be true, but many people don't look at lamps or such objects
    that are likely to cause halos. Also, vision is probably 80% psychology
    and maybe 20% physics, biochemistry, physiology and neurology combined.

    w.stacy, o.d.
    William Stacy, Aug 29, 2005
  14. Pauli Soininen

    p.clarkii Guest

    my clinical experience is that halos are indeed noticable but can
    become adapted to by many patients.

    i think it is an overstatement to say that uncompromising distance and
    near acuity equivalent to spectacles without ghost/halo is achievable
    with simultaneous vision multifocal contacts. it is doable however
    with translating RGP bifocals, but many patients cannot tolerate the
    discomfort of RGPs.
    p.clarkii, Aug 30, 2005
  15. That may be true, but many people don't look at lamps or such
    They don't have to be especially looked at. Unless 1) you really don't care
    what and how you see or 2) the vision in fact is so good that it can be
    called practically excellent, then you won't notice the imperfections.
    In my opinion maybe something like 70% optics, 20% neural
    filtering/optimization/adapting and 10% physical condition. Of course, there
    are exceptions, but in general (or averagely), I think the "spiritual state"
    can affect vision relatively little. I say this even I'm actually a
    supporter of great possibilities of the brain. After the optics, the
    sensation is heavily processed by the brain, but still, the optics are there
    and there are tasks not even the brain can manage. With proper tests,
    detailed visual qualities can be tested too, there is no need to be
    uncertain how one sees, it can be tested (with relatively simple methods).
    Pauli Soininen, Aug 30, 2005
  16. Pauli Soininen

    RM Guest

    I agree with you regarding the relative importance of optics vs. neural

    I vaguely recall some discussion of this topic during my PhD training in
    physiological optics. The upshot of the discussion was that precision of
    the optics of the retinal image is the single biggest contributor to the
    reported visual acuity by an observer. Sorry I cannot provide details;
    I've slept a few times since then.

    On the other hand, clinically I have seen many patients who happily accept
    less than optimal optics in return for convenience, etc. IMHO, it's all
    about pre-educating patients about what they should expect from multifocal
    contacts. They are not perfect but they can provide a lot of advantages
    that can outweigh the optical disadvantages to some people.

    RM, Aug 30, 2005
  17. Pauli Soininen

    The Real Bev Guest

    No. They moved/rotated out of position whenever I blinked or moved my eyes.
    Every once in a while they would land in the right place purely by chance, but
    would move away as soon as I blinked or moved. Absolutely useless for any
    practical purpose.
    Yes, exactly that. Close-up view of the veins on leaves, distant view of the
    TV antennas up in the mountains. As good as I get with glasses.
    The Real Bev, Aug 30, 2005
  18. Pauli Soininen

    LarryDoc Guest

    And so I cite myself as a case in point.

    My Tangent Streak RGP multifocals provide incredibly precise vision from
    distance to about 16"/40cm. They are 50% of the time at least noticeable
    and 10% of the time downright uncomfortable----but I persist in wearing
    them because I really enjoy the convenience of great vision without

    My soft multifocals (a couple of aspheric types of similar designs)
    provide reasonable distance and intermediate vision and fair near point
    optics. Sometimes I'll need +1.00 "readers" to help. They are perfectly
    comfortable 95% of the time, yet I prefer to use the RGPs instead. I use
    the soft primarily for sports and beach use mostly because critical
    acuity is not that important (my tennis game isn't that great and
    surfing/ocean swimming doesn't demand great vision) and I wouldn't want
    to loose/damage my RGPs!

    I have many patients who have very similar issues. And I will repeat
    that I have quite a few patients who have excellent vision at all
    distances---even a couple with toric soft multifocals, although I find
    it that much easier to achieve with RGP aspheric or segmented lenses.

    Sure, some people wont be satisfied with multifocal contact lenses and
    some "adapt" to and enjoy the freedom and deal with the compromise. And
    some have little or no compromise.

    Personally, I really dislike spectacles. Even my progressives custom
    fitted by the lab representative from one of the premier manufacturers.
    But that's me. Everyone has different needs and expectations. I makes my
    day interesting! Speaking of to work!

    --LB, O.D.
    LarryDoc, Aug 30, 2005
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