Question about cylinder axis

Discussion in 'Optometry Archives' started by Dick Adams, Oct 23, 2005.

  1. Dick Adams

    Dick Adams Guest

    Could one of the good eye doctors kindly answer this for me:

    Let's say I have a cylindrical correction at 45 degrees in the
    lens over my right eye.

    Considering a Cartesian coordinate system, and assuming the
    axis of the cylindrical aspect of my eyeglass lens is indicated
    by a 45 degree line drawn on the lens, would I see, as I
    look out through the lens, the line in upper right or upper left

    The question relates to whether the eyeglasses are considered
    as being viewed from the wearer's side, or the world side.

    Is the convention the same for the left eye as for the right,
    or flipped horizontally in the interest of bilateral symmetry?

    Thanks in advance for any help on this.
    Dick Adams, Oct 23, 2005
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  2. Interesting. My prescription supports that statement (they're 15 and 155).
    Woon Wai Keen, Oct 23, 2005
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  3. Dick Adams

    Dick Adams Guest

    Thank you. I have recorded that. Now one more question, please:

    If I orient a grid, like a square of graph paper, so that one set of lines
    is sharp at some distance d (cm), then move my eye to the distance d'
    where the other set of lines are sharp, is it true that the amount of
    my astigmatism is

    [100/d - 100/d']


    Or what?

    Thanks again.
    Dick Adams, Oct 23, 2005
  4. Yes. The gap between the first meridian that is clear, and the second
    meridian 90 degrees away when it is clear, is called "The Interval of
    Sturm". Your method is accurate if you could hold the axis of the grid
    exacly on the axis of your astigmatism, which is very hard to do. You
    can get a very good estimate of your astigmatism by looking at a grid
    as you described.
    doctor_my_eye, Oct 23, 2005
  5. Yes, assuming accommodation remains unchanged via cycloplegia,
    pseudophakia or some other mechanism...

    William Stacy, Oct 23, 2005
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