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    Effects of astigmatism greater on multifocals than monofocals IOLs

    How various magnitudes and manifestations impact optical quality, patient satisfaction

     

    Axis of astigmatism

    Another important factor to consider is the axis of the astigmatism. The investigators found that the neural system is highly tuned to horizontal and vertical gratings, but not as much to oblique gratings.

    “We perform better in interpreting images with horizontal and vertical images than oblique images, resulting in about a 50% reduction in image quality,” Dr. MacRae said.

    Against-the-rule or with-the-rule

    Studies of myopic against-the-rule astigmatism have shown that patients can see better during near vision tasks compared with patients who have with-the-rule astigmatism.

    “The phenomenon that occurs is that patients tend to ‘cue off’ of vertical letters, such as p, q, or t,” he said.

    Dr. MacRae and colleagues found that patients who had myopic against-the-rule astigmatism obtained a better image of a poster with the word “Rochester” printed on it than those with with-the-rule astigmatism because the vertical letters stood out.

    With distance tasks, the opposite is true. Patients with with-the-rule myopic astigmatism obtained slightly better images because of the vertical letters being presented.

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