Which Prescription To Use

Discussion in 'Optometry Archives' started by unknown, Oct 12, 2008.

  1. unknown

    unknown Guest

    It seems that the last optometrist I went to messed up with my
    prescription for my right eye, higher then it should have been, then
    when I went back to him again, he just keep increasing the spherical
    values for both eyes.

    As a result, I went to two other optometrists this time and got two
    prescriptions which were slightly different in the axis value for
    astigmatism. How do I know which one is a better fit?

    Are aspherical lens good if you have astigmatism? Is 1.60 index okay
    for this lenses? I would like my new pair of lenses to be the same as
    my old pair but don't know if it is 1.60 or 1.67.

    #1 #2
    Sphere -5.75 -5.50
    Cylinder -0.25 -0.25
    Axis 075 090

    Sphere -6.25 -6.00
    Cylinder -1.00 -1.00
    Axis 150 150
    unknown, Oct 12, 2008
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  2. unknown

    Mark A Guest

    The Rx you get is determined by the answers you give the OD when they ask
    you which is better (1 or 2, etc). Not every patient gives the same answers
    every time. Sometimes an OD is less thorough then they should be, which
    could also account for the difference. You could always go back to one (or
    both) of the OD's and mention the discrepancy and see what they say. I think
    most would be willing to double check it for free.

    Almost everyone who needs moderate or stronger correction has some
    astigmatism, and that is usually not a consideration in whether to get an
    aspheric lens. An aspheric lens is often used with a high power lens (such
    as the one you need) to keep the thickness down. The main drawback of an
    aspheric lens is that it requires very careful fitting so that the optical
    center of the lens is in the correct position in front of your eyes once the
    lenses are mounted in your frame. This requires careful fitting of the
    frame, fitting height, and pupil distance.

    You have a fairly strong Rx, so a 1.67 would make your lenses thinner
    (especially at the edges on your lens) and lighter than a 1.60, but the
    optical quality (amount of chromatic aberration measured by abbe value) of
    the lens suffers somewhat as the index gets higher (except for 1.59 polycarb
    which has even worse optical quality than 1.67). It is up to you to make a
    decision on the aesthetic versus optical quality issues when choosing your
    lens material. However, in some cases a lighter lens may enable your glasses
    to remain better positioned on your nose without slipping (which can be a
    problem for an aspheric lens), so it could actually be better for vision
    quality than 1.60 in that situation.
    Mark A, Oct 12, 2008
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