Focus Night & Day update

Discussion in 'Optometry Archives' started by Lothar of the Hill People, Oct 29, 2003.

  1. For those of you who have so kindly been commenting on my contact lens
    experiences lately... I went back to my lens fitter today, intending
    to tell her that my Focus Night & Day lenses were not working for me
    (because they were frequently blurry, which I assumed were because
    they were getting coated with lipids) and I was interested in trying
    Proclear Compatibles instead. She was very willing to try me on the
    Proclears, saying that it was one of her two favorite lenses that are
    currently available (Focus N&D being the other), but when she checked
    the power on my Focus N&D's, it was apparent that I needed a -0.5D
    stronger prescription in both eyes. She looked at my lenses through
    the lamp, both on and off of my eyes, and didn't notice the oily film
    that I thought I had noticed in the past (although she did notice some
    small white spots). So she gave me a pair of the revised Focus N&D
    prescription, as well as a pair of the Proclear Compatibles, and told
    me to feel free to experiment and see which worked best.

    What I do not understand (nor did she) is why I needed such a stronger
    prescription than I did 8 days ago when she first fit me with Focus
    N&Ds. At that time, my vision was somewhat blurry in her office in
    one eye (in both eyes, actually, but much more noticeably in my right)
    and wouldn't get any better no matter what corrective power she put in
    front of my lenses. Over the course of the following week, my vision
    was slightly blurry quite a lot of the time, which drove me nuts.

    So I guess my question is, has anybody else noticed any similar
    changes in prescription of these lenses over the course of a week, or
    have any possible explanations for this observation? Also, what do
    you think is the best way to compare this new power with the Proclear
    Compatibles--should I put one in each eye, or should I try the same
    lens in both eyes, alternately, for a few days? My fitter didn't seem
    to have a preference.

    Lothar
     
    Lothar of the Hill People, Oct 29, 2003
    #1
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  2. Lothar of the Hill People

    Dr. Leukoma Guest

    I have observed that the corneal curvature can be induced to change with
    thick, stiff lenses like the Focus N&D. In fact, I recently saw such a
    patient who is a high hyperope. Her prescription is so high that even with
    the highest plus available in the Focus N&D, she still needs to wear
    spectacles over the top. I just upped her prescription in June, yet just
    four months later she needed another 0.50 diopter increase. Sure enough,
    the topographies showed a flattening of the central cornea.

    Now, you might wonder why this woman is wearing the contact lens. She is
    in fact blind in one eye from amblyopia. Her good eye has epithelial
    basement membrane disorder. With very thick and heavy spectacles, she is
    correctable only to 20/30. With the Focus N&D, she only needs a spectacle
    prescription of +3.00, and can be corrected to 20/20. However, that's not
    the end of the story. Despite the fact that her cornea is being made
    flatter, it is also being made smoother, because she is now correctable to
    20/20 without the aid of the contact lens.

    So, perhaps your cornea is being made steeper centrally by the lens. Or,
    perhaps the lens is relatively steep to your corneal curvature, in which
    case a plus tear lens is being formed by between the back surface of the
    contact lens and the anterior corneal surface, which requires an extra
    amount of minus in the lens to neutralize. Or, you just coincidentally got
    more nearsighted.

    DrG
     
    Dr. Leukoma, Oct 30, 2003
    #2
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  3. Well that was certainly a very interesting response, DrG! It was
    interesting to hear of similar experiences that you've had with
    patients...

    Do you think this is a phenomenon that I might expect to continue, or
    a one-time change? I certainly don't want to make my eyes worse by
    wearing contact lenses! I chose Focus N&D because I thought they
    would be *better* for my eyes than any other lens. Are the changes
    that you've noticed something that can happen over the short span of
    time that I've noticed (less than a week), or is it more of a gradual
    change?
    This is beginning to make me nervous.

    Considering how relatively flat my K readings are (41-something), I
    suppose it's possible that the BC 8.6 lenses are so steep that they
    are doing what you are describing. I wonder if it is not a good idea
    for people with flat K readings to wear a stiff lens like Focus N&D?
    If I was becoming more mypoic, for whatever reason, I would think that
    I would be noticing a change in my vision when I am wearing my
    eyeglasses when I remove my lenses at night. I am not--my vision in
    my glasses is still better than it is when I am in my contacts, even
    with this revised contact lens power. I really hope I am right about
    that.

    I'm thinking I better have my doc test my vision in my glasses next
    time I go in.

    Lothar
     
    Lothar of the Hill People, Oct 30, 2003
    #3
  4. Lothar of the Hill People

    LarryDoc Guest

    If the cornea flattens, there is a DECREASE in myopia or an INCREASE in
    hyperopia.

    In my experience, about half of patients who previously used "the old
    kind of" soft lenses, especially for extended wear, showed an initial
    (one week of N&D) power change of +.25 to +.50. A significant minority
    of those, and nearly 100% of those who slept in lenses continued to show
    less myopia (or more hyperopia) over the next 3 weeks.

    Some of this is related to small changes in the cornea topography
    resulting from the "stiffer" silicone hydrogel, and some related to
    "decompression" and reversal of cornea edema caused by the former low DK
    lenses.

    Just yesterday, a former -8D extended wearer patient, over a three week
    period of time became a -6.50 myope-----and required three lens power
    reductions of the time. She showed almost NO change in cornea
    topography (so that 1.5 change appears to be from swelling) and a marked
    DECREASE in "my eyes are always red in a circle around the cornea".

    Of course in real life, functionally, thst 1.5 change makes little
    difference. But it does show the HUGE benefit afforded by dispensing
    properly designed and fitted contact lenses. Instead of "this is what
    we've got in stock today" or "the cheapest lens from scamming an on-line
    reseller".

    Gotta love it!

    --LB

    --
    Dr. Larry Bickford, O.D.
    Family Practice Eye Health & Vision Care

    The Eyecare Connection
    http//www.eyecarecontacts.com
    larrydoc at m a c.c o m
     
    LarryDoc, Oct 30, 2003
    #4
  5. Wow, this is getting more and more interesting...

    Not being a doc, I have no idea what happens medically, but
    intuitively it would seem to me that if I am wearing a lens that is
    steep relative to my cornea, which I would guess is more likely for me
    because my K readings are somewhat flat, then it would sort of
    "squeeze" the cornea into a steeper topography, like what would happen
    if you squeezed the top of a balloon with your hand. Am I visualizing
    this properly? If so, then based on what you said above, I should be
    getting more myopic over time, which *seems* to be what happened to me
    over a span of the last week.
    Those are certainly some fascinating statistics, Larry! I rarely
    slept in my last pair of (non-silicone) lenses, so I am guessing that
    any changes going on in my cornea are not due to a "healing" of edema
    due to renewed oxygen availability. I could be wrong though--you'd
    know better than me. I am definitely interested in trying extended
    wear in these Focus N&Ds, so perhaps I can expect my power to reverse
    and go back down to where it was before!

    My lens fitter did tell me that in her experience, people who wear
    Focus Night & Day lenses tend to need a more negative power than they
    would with other lenses. That made me wonder if CIBA labels the power
    of these lenses differently than other manufacturers do, but now I see
    that it may be due to corneal changes.

    I find that fascinating!

    Lothar
     
    Lothar of the Hill People, Oct 30, 2003
    #5
  6. Thanks, that is comforting.
    Let's assume for the moment that the fit is the reason why my power
    apparently changed so quickly, and I am getting this "plus tear lens"
    forming behind the contact lens. In your experience, is it likely that
    my eyes will adapt favorably to this condition, or this an indication
    that the lens could be too steep for me to wear safely? I don't really
    know what other symptoms I should be looking for to determine if my
    lenses are too steep, and my fitter didn't say anything about them
    looking too steep when she examined my eyes this week.
    I hope it is small stuff, but thanks for reassuring me!

    Lothar
     
    Lothar of the Hill People, Oct 30, 2003
    #6
  7. Lothar of the Hill People

    LarryDoc Guest

    Nope. Due to the plus tear lens. Lens power is lens power and ,
    assuming the machinery marks the container correctly, that what it is.
    What the *effect* of that power is, on the other hand, depends upon how
    the lens fits over the cornea.

    So, some people need more minus power and some don't.

    --LB

    --
    Dr. Larry Bickford, O.D.
    Family Practice Eye Health & Vision Care

    The Eyecare Connection
    http//www.eyecarecontacts.com
    larrydoc at m a c.c o m
     
    LarryDoc, Oct 31, 2003
    #7
  8. So are the people who need more minus power the people whose lenses
    aren't fitting properly? Or can a plus tear lens form in people with
    an acceptably-fitting (from the perspective of both comfort and
    safety) lens? It would seem to me (intuitively) that if a lens is
    perfectly fitted, then it should be exactly the same power as what was
    prescribed for eyeglasses.

    Incidentally, last night I self-tested my visual acuity both with my
    eyeglasses on and with my contacts in (in my revised more negative
    power) on a Snellen-type eye chart. I was barely reading the 20/20
    line using either, maybe slightly sharper with my contacts on. Before
    I started wearing Focus N&D, my vision always seemed sharper with my
    eyeglasses (although I never measured it). The power of my contacts
    is now -0.50D stronger than the power of my glasses. Does that tell
    anybody anything useful?

    Lothar
     
    Lothar of the Hill People, Oct 31, 2003
    #8
  9. Lothar of the Hill People

    Dr. Leukoma Guest

    How does one go about a perfect fitting with a lens that comes in one
    diameter and only two base curves? Let's dispense with that notion at
    once. Typically, the fitter evaluates soft lenses based on position,
    movement, acuity, and surface condition. It is possible for a lens to fit
    too tightly, and yet the base curve can be entirely appropriate for the
    central cornea. If it fits too loosely, the patient will have lens
    awareness. The term "acceptable" fit is much more appropriate in a
    clinical setting than "perfect" fit.

    Here is a scenario in which the eyeglass prescription and the contact lens
    prescription cannot be identical or produce identical results. The patient
    has a small amount of residual astigmatism that cannot be put into the
    contact lens. The only way a fitter has to correct this error is an
    "approximation" by increasing the sphere power of the contact lens by one-
    half the amount of the cylinder, whereas the entire cylinder correction can
    be supplied in the eyeglasses.

    If the power of your contact is 0.50 stronger than your eyeglasses, and the
    visual acuity is slightly better than with the eyeglasses, this tells me
    that your spectacle prescription "might be" off by 0.50 diopters or less,
    but there can be other causes. Try comparing the two early in the morning
    after having had the lenses out overnight, or perhaps wait a couple after
    removing the lenses to make the comparison.


    DrG
     
    Dr. Leukoma, Oct 31, 2003
    #9
  10. Excellent point, and well-taken! As a patient, is there a way for me
    to help evaluate whether the lens is too tight, or is only something
    that can be determined in a doctor's office?
    Very interesting. I suppose I should have posted my eyeglasses
    prescription here. As of May 20 of this year, it was OD -2.00, no
    cylinder or axis, OS -2.00, -0.50 cylinder, 25 axis. At my previous
    eye exam 3 years earlier, my prescription was exactly the same except
    that my OS axis was 30. Considering how stable my vision has been
    over the years, I would be surprised if my myopia coincidentally
    increased during the brief time that I've been wearing Focus N&D.
    I actually already did exactly what you just suggested. I compared
    eyeglasses vs. contacts this morning, after having the lenses out
    overnight, and also last night shortly after removing my lenses. Here
    are my Snellen estimates that I made (estimated based on how clear I
    felt the 20/20 line was in relation to the next line on this chart,
    20/40):

    with contacts (PM of October 30):
    L 20/25
    R 20/25

    with eyeglasses (PM of October 30):
    L 20/30
    R 20/30

    with contacts (AM of October 31):
    L 20/20
    R 20/20

    with eyeglasses (AM of October 31):
    L 20/25
    R 20/20

    If my eyeglasses prescription is indeed off, then it is a new
    development, because they were fine before I started wearing contacts.

    Thanks for your continued helpful insights, DrG!

    Lothar
     
    Lothar of the Hill People, Oct 31, 2003
    #10
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