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[A corneal topographic analysis of astigmatism after excimer laser photorefractive keratectomy].

OBJECTIVE
To identify the astigmatism changes after excimer laser photorefractive keratectomy (PRK) and the visual influence of astigmatism.


METHODS
109 myopic eyes followed up for more than 1 year were analyzed by using videokeratography, and their visual acuities were examined. Before the operation, the astigmatic errors with cycloplegic refractive examination were -1.00(-)-2.00 D.


RESULTS
The position of astigmatism axis was basically consistent with that in corneal topography, but the astigmatism diopter was of some difference between the cycloplegic examination and topographic analysis. With-the-rule astigmatism was in 61% of the eyes, asymmetrical was 33% and against-the-rule was 6% in topographic analysis. Only was a little change in the position of astigmatism axis after PRK observed. Some changes of postoperative astigmatism diopter were seen in different periods. It was increased in the postoperative 10 days or 1 month, and afterwards it became gradually decreased and stable in 6 months to 1 year. The postoperative residual astigmatism was low in degree, that did not affect the visual acuity a great deal. The actual corrected diopter was within the anticipated corrected diopter range of +/- 1.00 D, accounting for 97%.


CONCLUSION
By using spherical equivalent method of calculation in PRK, the refractive correction of the operation in cases with myopia and low degree of astigmatism (< -2.00 D) can be satisfactory.