eyeglass prescription question

Discussion in 'Glasses' started by Doug, Jan 12, 2005.

  1. Doug

    Doug Guest


    I have a question about my eyeglass prescription. I am near-sighted and
    have some amount of astigmatism in both of my eyes.

    My question is about the prescription. It is written as

    Sphere Cylinder Axis
    OD -7.25 +0.50 88
    OS -7.25 +1.50 98.

    I am confused about the Cylinder values. Isn't it true that
    near-sighted people like me should have negative cylinder values
    instead of positive ones? Please let me know what the cylinder values
    mean. Thanks!

    Best Regards,
    Doug, Jan 12, 2005
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  2. Doug

    drfrank21 Guest

    Optometrists usually write in minus cylinder form versus
    the plus cylinder form (as in your rx) written mostly
    by opthalmologists. Basically, you can transpose (switch)
    into either form using a simple formula. The cylinder
    values just express the amount and orientation of your
    astigmatism (irreg curve of your corneas).

    drfrank21, Jan 12, 2005
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  3. Doug

    Guest Guest

    You may translate your prescription as follows, it is still the same power.
    Notice the - (minus) sign and the change in degrees (90degree difference)
    All to international agreements (TABO)

    OD S-6.75 = C-0.50 178
    OS S-5.75 = C-1.50 8

    In Europe we are used to prescribe with the - (minus) sign notation for the
    astigmatic part of the prescription.
    Guest, Jan 12, 2005
  4. I and others here have written here about this subject before. With
    computers being used more and more, the confusion is readily soluble. A
    computer can be use to translate from sphere/cylinder/angle to sphere/0°
    astimatism/45° astigmatism or back. The first form is ambiguous. The second
    form is not. The first form can become the legacy form used to interpret old
    prescriptions. Both forms can be put onto a computer written prescription.

    The second form uses two orthonormal Zernike functions to represent
    astigmatism. Using that allows only one unambiguous value for the spherical
    correction. These Zernike functions can only be approximated using
    cylindrical lenses. These days however, with wavefront correction in vogue,
    even spectacle lenses may end up being corrected for higher order

    This gets me to a question about the preparation of spectacle lenses. Are
    such lenses fabricated the same way irrespective of wether
    optometrist/ophthalmologist notation is used?

    Repeating Rifle, Jan 12, 2005
  5. Doug

    Guest Guest

    Guest, Jan 12, 2005
  6. So how is it done? Is only one surface shaped? Is the sphere on one side of
    the blank and cylinder on the other? If this last case is true, how does the
    optician set the sphere?

    Repeating Rifle, Jan 13, 2005
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