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 videokeratography, and their visual acuities were examined, Before the operation, the astigmatic errors with cycloplegic refractive examination were -1.00 similar to-2.00 D. Results The position of astigmatism axis was basically consistent with that in corneal topography, but in astigmatism diopter there were some differences between the cycloplegic examination and topographic analysis. A stigmatism was found in 62% of the eyes, asymmetrical in 33% and against-the-rule in 5% by using topographic analysis. There was little change observed in the position of astigmatism axis after PRK observed. Some changes of postoperative astigmatism diopter were seen in different periods. It increased in the postoperative 10 days or 1 month, and afterwards gradually decreased and became stable in 6 months to 1 year. The postoperative residual astigmatism was low in degree, and did not affect the visual acuity. The actually corrected diopter was within the anticipated corrected diopter range of +/-1.00 D, accounting for 97.4%. 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) was satisfactory.