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J.C. Merriam, L. Zheng, J.E. Merriam; Change in the Axis of Corneal Astigmatism after Cataract Surgery . Invest. Ophthalmol. Vis. Sci. 2003;44(13):231.
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Purpose: To determine the effect of 5 common incisions for cataract on the axis of the keratometric meridians of the cornea. Methods: This is a retrospective review of 662 cases of cataract operated by a single surgeon prior to 1999. The meridians of the cornea were measured with a keratometer. The steeper axis at each visit was stored in FileMaker Pro and sorted to the following intervals: preop, day 1, 1 week, 2 weeks, 4 weeks, 6 weeks, 2 months, 4 months, 6 months, 12 months, and to 6 month intervals thereafter. The principal meridian was considered vertical if it was within 15º of 90º, horizontal if within 15º of 180º, or oblique if within the ranges 16º to 74º or 106º to 164º. When the difference between the major and minor axes of the cornea was less than 0.5 diopters, the cornea was considered spherical. The relative frequency of each of these 4 subgroups was calculated at each post-operative interval. The 95% confidence interval of a curve fit to the data shows the prevalence of each subgroup over time. Results: Compared to the preoperative prevalence of each subgroup,ECCE leads to less vertical or no astigmatism and an increase in the prevalence of oblique and horizontal astigmatism. Similar but smaller changes in prevalence of the 4 subgroups were detected after 6Sup and 3Sup. A small but significant increase in oblique astigmatism and a small decrease in horizontal astigmatism were detected after 3Temp, and a very small increase in oblique astigmatism was detected after 3Cor. Conclusions:The size of a wound on the superior meridian has a significant effect on the axis of the steeper meridian. Three mm incisions on the temporal meridian have less effect on the axis of corneal astigmatism than a 3 mm incision on the superior meridian.
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