RGP residual astigmatism

Discussion in 'Optometry Archives' started by Charles, Oct 24, 2006.

  1. Charles

    Charles Guest

    I've got my RGP's dialed in pretty well. The doc "maxed out" the
    diameter and the OZ and fixed most of the trouble I was having with
    night vision issues and seeing the edges. The last small complaint I
    have is that the vision is slightly variable in one eye (tack sharp
    perfect in the other). More often than not, I think I have about 0.25D
    of astigmatism remaining, which I can occasionally blink away, and that
    seems to come out more when my eyes are more dry.

    I intend to ask my doc the same questions, but to the docs on the list,
    what do you think might be causing this, and are there things that can
    be adjusted to try and fix it? I don't think I had this when the
    lenses were smaller (but the problems with them were far more
    annoying). My layman's guess would be that maybe the larger lenses may
    cause this if they cover more severe astigmatism toward the edge of the
    cornea, and flex around it (?). Might a stiffer lens material help?

    Charles, Oct 24, 2006
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  2. Charles

    LarryDoc Guest

    Geez, you ARE demanding, eh? Are you down to 20/12 yet? Ready for
    wavefront? Meanwhile......

    Your theory of the lens flexing and using a stiffer material is a
    definite consideration. If your lens is not already aspheric optically,
    you might try that. If it is so, then you might want to *reduce* the
    asphericity in the periphery leaving the OZ the same.

    LB, O.D.
    LarryDoc, Oct 24, 2006
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  3. Charles

    CatmanX Guest

    Sorry Charles your layman's theory is wrong.

    Residual cyl is from lenses flexing or lenticular astigmatism. Larger
    lenses will do nothing for the cyl. Depending on whether your cyl is
    central or peripheral, a spherical lens may correct the cyl or you may
    need a back surface toric if the toricity extends to the limbus.

    I would not bother to correct the additional -0.25, it is pretty well
    irrelevant and will not improve vision any in most cases.

    CatmanX, Oct 24, 2006
  4. Charles

    Jan Guest

    Charles schreef:
    Residual not corrected astigmatism of 0,25 diopters when wearing RGP's
    is a marvelous result.
    Theoretically your may try to compensate it with a toric lens if you
    are wearing a spherical one now but the outcome is more worse, believe me.
    The toric lens gives a perfect view in just one position, however when
    the lens rotates out of this exact position you create a so called
    crossed cylinders situation which create another optical error.
    Also the used optical zone gets an oval shape and this also can lead to
    more problems.
    I almost forgot to mention the needed prisma ballast, another possible
    complain issue.
    And as a result you, Charles, are the one that shall complain even more
    as you are already.

    Jan (normally Dutch spoken)
    Jan, Oct 24, 2006
  5. Charles

    Charles Guest

    Are we saying the same thing then? Lens flexure? I was just trying to
    understand why I didn't have this with the small lenses. Of course,
    having changed docs in-between, I don't know what else also changed.
    Well, I guess that's subjective. I can read the 20/20 line with both
    eyes, but I always have my "perfect" right eye to compare against,
    which makes the blur in the left noticeable. With both eyes open, I
    can tell I'm leaning on my right eye to make out street signs far away.

    I'm not complaining, but if I can dial it in, why not?

    Charles, Oct 24, 2006
  6. Charles

    Charles Guest

    Agreed, toric is not even on the table for only 0.25D.

    The funny thing is that the eye with the residual error is the one with
    0.5D less astigmatism in the glasses Rx.

    Charles, Oct 24, 2006
  7. Charles

    Charles Guest

    Just for sake of me learning something, in what way might this help
    address residual astigmatism?

    Charles, Oct 24, 2006
  8. Charles

    Jan Guest

    Charles schreef:
    I can order such a lens, no problem.
    Could be quite normal, depends on the cornea curvature related to the
    error in refraction (your astigmatism).
    If the astigmatic curvature of the cornea is optically speaking
    corresponding exactly with the prescribed cylinder, you can compensate
    the amount off astigmatism about 90%.

    If the two do not match you have to deal with the rest astigmatism
    caused inside the eye.
    In this way you can imaging a spherical prescription for glasses and a
    toric one for a RGP contactlens. (toric cornea versus spherical error in
    total refaction)

    Jan (normally Dutch spoken)
    Jan, Oct 24, 2006
  9. Charles

    Quick Guest

    Not sure if this is even related but I had 0.25 astigmatism
    in my right eye when I started with my RGPs over 6 months
    ago. I had him do another refraction last week and it seems
    it's gone now. No change in prescription or noticeable difference
    in vision, but it's gone (orthok effect I guess?)

    Quick, Oct 24, 2006
  10. Charles

    Charles Guest

    Good data point. I was wondering if it might go away with time.

    Charles, Oct 25, 2006
  11. Charles

    Jan Guest

    Charles schreef:
    Small changes back and forth are quite normal over a longer period of time.
    And yes, RGP lenses changes the cornea a little bit due to the massage
    effects and the little metabolism changes when changing from wearing RGP
    lenses to not wearing those.

    This is one off the reasons why you can not prescribe exact correcting
    spectacles for wearing occasionally next to this type of lenses.

    Jan (normally Dutch spoken)
    Jan, Oct 25, 2006
  12. Charles

    Charles Guest

    After only a month or so in my new lenses, my astigmatism is almost
    totally gone between wearings. In well lit places, I have perfect
    vision with no lenses (I was as high as -1.5D cyl in one eye). In the
    dark it's not as good, but still probably less than 0.5D I'd guess.
    The reshaping must be more pronounced in the center of the cornea.
    This would make sense since my dark night vision is still imprefect
    even with the lenses on (apparently I have a large pupil).

    It's worked so well that I asked again whether overnight ortho-k was an
    option. If it works this well as an accidental side effect, shouldn't
    it work better if you design for this effect on purpose? The answer
    still came back "no" though.
    Charles, Oct 25, 2006
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