Bitoric RGPs

Discussion in 'Optometry Archives' started by silverblue001, Jun 15, 2005.

  1. Just wondering ...in what circumstances would bitoric RGPs be required?
    Are they usually difficult to fit? All I know about them right now is
    that they're going to put a large hole in my wallet. ;)
     
    silverblue001, Jun 15, 2005
    #1
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  2. Only when soft lenses won't work and spherical gas perms also won't
    work. Usually it's when there is a whole lot of astigmatism and/or the
    total astigmatism doesn't "match" the corneal toricity. I haven't used a
    bitoric in several years, mostly because toric soft lenses have gotten
    pretty good.

    w.stacy, o.d.
     
    William Stacy, Jun 15, 2005
    #2
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  3. Oh, and about the difficulty of fitting, not particularly, since "the
    lab" does most of the calculations. There's a certain amount of voodoo
    optics involved, in fact it is the one area of ophthalmic optics I
    personally had trouble with in college, which is why I always let the
    lab figure it out, based on K readings & refractive error.

    If you'll post those 2 items, I can tell you whether bitorics are
    indicated or not.

    w.stacy, o.d.
     
    William Stacy, Jun 15, 2005
    #3
  4. silverblue001

    Guest Guest

    They (the lab) give you also advise in fitting, thinking about the two inner
    radi William?
    Why should people wanted there lenses fitted by you if your lab decide what
    the data outcome of the contactlens should be?

    One nice thing in fitting contactlenses is to be sure why you wanted the
    contactlens just a bit flatter, steeper, smaller, larger, fronttoric,
    innertoric, etc ect.
    Your contactlens-lab can't observe the movement or just the lack of it, they
    are not capable to check the tearflow between lens and cornea etc.

    No William, I certainly do not agree with you when your saying ''Oh, and
    about the difficulty of fitting, not particularly''

    For the ''voodoo'' part, I leave that to Otis, he is so familiar with the
    right use of chickens.
    --
    Free to Marcus Porcius Cato: ''Ceterum censeo Carthaginem esse delendam"

    In conclusion, I think that the "Otis therapy" should be destroyed

    Jan (normally Dutch spoken)
     
    Guest, Jun 15, 2005
    #4
  5. Actually, they do offer expert advice on the fitting, and even base
    curves. They have experts who make hundreds of these lenses a year,
    while I might not order one in a year or more. Obviously I'm going to
    give input based on trial lenses that I always evaluate on the eyes first.
    Because they can't legally go to the lab? Obviously the outcomes are
    evaluated by me, and the buck stops here.
    No argument there. I am the fitter, of course.
    Same answer. I was obviously referring to the INITIAL LENS SELECTION.
    I don't think the fitting is much more difficult than a spherical RGP if
    you have the help of a lab expert.


    touche'

    w.stacy, o.d.
     
    William Stacy, Jun 15, 2005
    #5
  6. silverblue001

    Dr. Leukoma Guest

    Is the size if the whole as large as the one my dentist puts into my
    wallet every six months?

    I would advise making a similar comparison.

    DrG
     
    Dr. Leukoma, Jun 16, 2005
    #6
  7. silverblue001

    Dr. Leukoma Guest

    Is the hole in your wallet the same size as the one my dentist puts in
    mine?

    DrG
     
    Dr. Leukoma, Jun 16, 2005
    #7
  8. silverblue001

    Dr Judy Guest

    Usually when you have significant astigmatism.

    With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and
    the back curve of the lens needs to be made toric. That back toricity
    results in the contact lens not correcting the refractive error so that a
    compensating toric surface needs to be placed on the front of the lens as
    well.

    With today's soft toric lenses, it is possible to fit a greater percentage
    of astigmats with a soft lens, however, with large amounts of corneal
    astigmatism, vision is clearer and more stable with a rigid lens and that
    usually means a bitoric.

    Fitting bitorics requires an experienced rigid lens fitter and experience
    with bitorics and an accurate lab. There is often some fine tuning required
    in the first few months. I have fit many bitorics and the bulk of the
    patients are quite happy.

    The good news for you is that it is a one time expense. The lenses will
    likely last 3-5 years. Compare your cost with the cost of disposable toric
    soft lenses for the same time period and you won't think the hole in your
    wallet is so big.

    Dr Judy
     
    Dr Judy, Jun 16, 2005
    #8
  9. Thanks for the input so far ...

    Unfortunately I had a horrible time with soft torics. On many days my
    vision was no better than about 20/60 or 20/70. It was pretty crazy.

    I'm not sure what a K reading is, so no luck there. It's also
    difficult to say what my cylindrical error is. Last year it was about
    4.25 R and 2.25 L ... this year it came out to be R 2.75 and L 1.75
    however it's not clear whether that was a "real" change or whether it
    was a temporary change caused by the soft contacts. The first trial
    lens that he put into my right eye felt absolutely horrible ... like it
    was "popping" up every time I blinked ...

    Gee that wasn't of much help, was it? ;)
     
    silverblue001, Jun 16, 2005
    #9
  10. Hmmmmm ....
    I see.
    Anything is better than the vision I had with soft torics! If my
    vision doesn't improve with RGPs, I think I'll end up giving up
    contacts all together. :S
    Hmmm ... well my CL fitter has been at it for 22 years and, from the
    way he speaks, he seems to have a lot of patients wearing them ...
    True. Unless my Rx changes again. :S
    Thanks!
     
    silverblue001, Jun 16, 2005
    #10
  11. Quite possibly. Luckily I don't have to worry about the dental bills
    just yet .... ;)
     
    silverblue001, Jun 16, 2005
    #11
  12. I don't know ...I'm a bit skeptical. I can't see how a contact
    lens could possibly slow/stop the progression of axial myopia. Sure it
    could flatten the cornea and thus temporarily change your Rx ... but in
    my mind it seems more it's masking any changes rather than preventing
    them from occurring ...
     
    silverblue001, Jun 16, 2005
    #12
  13. Wow, I'm surprise to hear that that little cyl would require a bitoric.
    It sounds like you fit lots of bitorics, and I can't even remember
    the last time I did. What's wrong with this picture? I remember fitting
    quite a few of them years ago, esp. in the days of PMMA, because we fit
    so small (8.5 mm, even less) lenses that corneal toricity did matter a
    lot. Nowadays, with the high DK lenses, I can fit nice big lenses that
    are very stable regardless of corneal toricity. I recently fit a VERY
    highly astigmatic keratoconus with a big spherical lens and it fits
    fine, and gives stable 20/20.
    I totally agree, although I don't much like the "fine tuning" idea.
    That's what I meant about voodoo optics. Seems like with torics
    predicting the result of a given lens on a given cornea is, well, a bit
    sketchy at best. What's the LOWEST amount of corneal toricity you will
    fit with a bitoric, and what's the usual diameter (or range thereof) of
    your bitorics?

    w.stacy, o.d.
     
    William Stacy, Jun 16, 2005
    #13
  14. It's more like postponing any increase that's going to happen, until you
    stop wearing lenses. With spherical (non toric) RGPs ometimes it does,
    sometimes it doesn't. I don't think bitorics offer much in that realm
    because they need to fit pretty much like a glove, so you can't really
    flatten the cornea much.

    w.stacy, o.d.
     
    William Stacy, Jun 16, 2005
    #14
  15. Even if vision is fully corrected with a spherical lens, a corneal
    astigmatism above 2D will cause too much rocking of the lens (with the rule)
    and be quite uncomfortable.

    It is quite simple to calculate the prescription of a bi-toric lens, just
    calculate the power at the axis and that perpendicular to it, then change it
    to its sphero-cylindrical form. The major problem is when the corneal
    astigmatic axis and the spectacle axis is quite a bit different. Calculation
    is still possible by adding the two cylinders together. An easier way to do
    this though, is to over-refract over a sperical lens, and give the lab the
    data.

    Roland J. Izaac
     
    Philip D Izaac, Jun 16, 2005
    #15
  16. Honestly, that's what I thought too. But according to my CL fitter,
    there was nothing else he could do for me. He said my only other
    option was to switch to RGPs ...
    Maybe not. Then again my lenses are quite thick ...

    I definitely didn't wear them day and night.

    I'm quite confident in the 4.25 and 2.25. Those numbers were
    determined post scleral buckle OU and have been quite stable over the
    past 4 years. My usual BCVA with glasses is 20/30 OU. After wearing
    the soft torics, my BCVA with glasses (w/ a cylinder of 4.25 and 2.25)
    deteriorated significantly (to around 20/60 or so). My ophthalmologist
    tried to correct it and came up with the 2.75 and 1.75. With that
    cylindrical correction, my vision was a (*very* blurry) 20/40. She
    played with the lenses for quite a while but nothing seemed to help, so
    we left it at that. To make things even more confusing (for me at
    least), last week I got my new glasses made (with the 2.75 and 1.75
    cylinder). I haven't been wearing contacts for about 3 weeks straight.
    My vision can again be corrected to 20/30 with these new glasses ...

    Is it possible that the contacts temporarily induced an irregular
    astigmatism that couldn't be corrected properly? Alternatively, is it
    possible that my astigmatism changed so drastically within the course
    of a year? I think this is going to drive me insane. :S
    As I said above, my BCVA with glasses is 20/30 OU. My Rx R -15.50 and
    L -15.00.

    The situation has been very frustrating. :(
     
    silverblue001, Jun 16, 2005
    #16
  17. silverblue001

    Dr. Leukoma Guest

    Soft toric lenses, especially in high prescriptions, can indeed change
    the cornea, resulting in corneal warpage. In fact, there is one study
    showing that the corneal warpage due to soft toric lenses can take
    months to resolve completely.

    With a prescription in the range of -15.00 with high astigmatism, I
    would also recommend an RGP lens, preferrably of hyper-DK material,
    such as Optimum Extra, Boston XO, or Menicon Z.

    DrG
     
    Dr. Leukoma, Jun 16, 2005
    #17
  18. 21.

    Hmmmm ... I don't think I'd want any more eye surgery though ... I
    think I've had enough for a lifetime ... plus, for me, the risks are
    not worth it ... my fear of having more RDs surpasses my desire to have
    good vision. :S
     
    silverblue001, Jun 16, 2005
    #18
  19. Hmmmmm .... I guess I'll have to consider that if things don't work out
    with the RGPs ...

    I wonder if my vision can get much better than what it is right now
    though ... :S
     
    silverblue001, Jun 16, 2005
    #19
  20. silverblue001

    Dr Judy Guest

    I've found over the years that large, spherical RGPs led to corneal molding.
    Also the sphericals "rock", decentre and I see more 3&9 staining. So,
    usually at 2D corneal cyl, I think about bitoric.

    Nowadays, with the high DK lenses, I can fit nice big lenses that
    Well, keratoconus is a different matter altogether. Though I have used
    bitorics on early keratoconics if there was decentration due to the
    eccentric cone.
    Predicting is quite good if you use trial fitting lenses. I have two trial
    sets of spherical effect bitorics (front toric surface exactly cancels back
    toric so the net power effect of the lens is spherical -- greatly simplifies
    over refraction) one with 2D back toric (good for up to 3D corneal cyl),
    one with 3D back toric (good for up to 4D corneal cyl) with flatter base
    curve increments in 0.50D steps from 41.00 to 45.00. All are diameter 9.0,
    though the lab can do larger or smaller.

    Most of the time I can fit the exact back curve I need, otherwise I fit each
    meridan with the closest lens. Usually the over refraction is close to
    spherical, if not, I provide the sphero-cyl, with axis, over refraction to
    the lab and they modify the front toric to match.

    Can't help the fine tuning, trial lenses can only do so much. I treat the
    first pair ordered as trials, assess the fit and over refraction after 2-3
    weeks wear then change if needed.

    I'm up front with the patients, tell them likely the first pair will not be
    the final pair and it may take two to three months of fiddling to get it
    right.

    Dr Judy

    What's the LOWEST amount of corneal toricity you will
    I once did a 1.50 corneal cyl due to problems with centration and comfort.
    Worked fine, though the lab called me to confirm that's how little I wanted.
    The most was 8D corneal cyl, the patient's spectacle Rx was something like
    +6.00 -7.00 x oblique. The 25 year old patient was very happy, as everyone
    else had always told him that he couldn't wear contacts and he was involved
    in sports.

    Dr Judy
     
    Dr Judy, Jun 16, 2005
    #20
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