Difference between these prescriptions?

Discussion in 'Optometry Archives' started by Ed, Dec 1, 2009.

  1. Ed

    Ed Guest


    I was wondering what the difference between these two prescriptions
    is. They are my mom's. The first one is from last year, and those are
    the glasses she is currently wearing and can see reasonably well

    The second one is new. She ordered glasses from Zenni and says she
    can't see well in the left eye. I had the glasses checked at two
    opticians' offices and they both said that the prescription is "pretty
    accurate". They both said the axis may be off a bit, but should be
    unnoticeable. I suspect her new eye doctor may have given her a
    prescription that may be wrong for her. (Notes: Lenses are
    progressive bifocals. And she can see much better from her old

    Last year...

    Sphere: +2.75
    Cylinder: -0.75
    Axis: 095

    Sphere: +3.25
    Cylinder: -1.25
    Axis: 105

    This year...

    Sphere: +2.00
    Cylinder: +0.75
    Axis: 180

    Sphere: +1.50
    Cylinder: +1.00
    Axis: 025


    Ed, Dec 1, 2009
  2. Ed

    Mark A Guest

    To translate the above in plain English:

    There are two ways to express a correction for astigmatism, one with a minus
    correction and the other with a plus. If an Rx uses a plus cylinder, then
    the sphere must also be changed if it is compared to an Rx with a minus
    cylinder. The net is that both Rx's are very close to each other if the
    adjustment for the plus cylinder is made.

    As noted, most plus cylinder Rx are written by ophthalmologists, who have a
    chip on their shoulder and want to feel superior to an optometrist who will
    usually use a minus cylinder. You do not need to get an Rx for glasses or
    contacts from an ophthalmologist unless you have some sort of eye disease or
    serous problem with your eyes (other than just needing correction).
    Mark A, Dec 1, 2009
  3. Ed

    Liz Guest

    Wouldn't a 90-degree change in the axis be rather noticeable? Isn't
    that what she's got here?

    Liz, Dec 4, 2009
  4. Ed

    Dr Judy Guest

    The prescriptions are very similar, one is in plus cyl form, the other
    in minus cyl form so they look different.

    Did she order the same brand of progressive and same material as the
    old pair? Progressives vary greatly in quality. The problem is
    likely to be centration of the lenses and adjustment of the frame.
    Progressives are very sensitive to placement, being 1 mm out will
    cause problems. And if the frame is not angled correctly they don't
    work well either.

    A major problem with Internet ordering of progressives -- how do you
    get accurate measures and a good frame adjustment?

    Dr Judy
    Dr Judy, Dec 4, 2009
  5. Ed

    Dan Abel Guest

    I don't pretend to understand why, but plus readings are always 90
    degrees off from minus readings.
    Dan Abel, Dec 4, 2009
  6. Ed

    Dan Abel Guest

    Well, obviously there must be some lenses inside of those gizmos, but we
    aren't talking about lenses, but about comparing prescriptions. If the
    diopters for cylinders is plus, then the degrees will be different by 90
    for the same prescription where the cylinders is minus.
    Dan Abel, Dec 4, 2009
  7. Ed

    Dr Judy Guest

    The axis changes depending on whether plus or minus cyl form. Cyl
    form is a shorthand for the full prescription.

    For example, full prescription is

    +2.00 along 180 axis with +3.00 along the 090 axis

    This can be written as
    +3.00 -1.00 x 180 (+3.00 along 90, subtract 1.00 dioptre from the 180)
    +2.00 +1.00 x 90 (+2.00 along 180, add 1.00 to the 90)

    All three prescriptions specify exactly the same lens.

    Dr Judy, Dec 4, 2009
  8. Ed

    Dr Judy Guest

    Both, but mostly design. Some older (and cheaper) designs have very
    narrow corridors and much more distortion.

    All progressives are aspheric. If you don't want aspheric, you must
    stick with a line bifocal or trifocal

    Dr Judy, Dec 4, 2009
  9. Ed

    Dan Abel Guest

    Thanks for your complete and succinct explanation. I have saved it for
    the next time this question comes up.
    Dan Abel, Dec 4, 2009
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