Standardized vector analysis of correction of astigmatism after Epi-LASIK

Objective To evaluate the correction of astigmatism after Epi-LASIK (epipolis laser in situ keratomileusis) by standardized vector analysis,and to investigate the factors that affect the outcome of correction.Methods Sixty-eight myopic astigmatism eyes treated with Epi-LASIK were divided into two groups,low-midrange astigmatism (0.00D ～-2.00D) group and high astigmatism (-2.25D ～-4.00D) group.The following-up period was for 6 months.The astigmatism status wasevaluated based on the standardized vector analysis which was recommended by the American National Standards Institute.Results The CR (correction ratio) was positively correlated with IRC (absolute intended refractive correction) (r =0.82,P ＜0.05).The ER (error ratio) was negatively correlated with IRC (r =-0.61,P ＜0.05).The EA (absolute error of angle) was negatively correlated with IRC (r =-0.74,P ＜0.05).The EV (absolute error vector) of low-midrange astigmatism group was significant lower than that of high astigmatism group (P ＜0.05).The EM (error of magnitude) of low-midrange astigmatism group was-0.12±0.15 and EM of high astigmatism group was-0.14±0.42.Conclusions The effectiveness of the correction of astigmatism after Epi-LASIK is closely correlated with that of axis alignment of astigmatism,and the diopter of astigmatism which is set as surgery parameter shall be transferred from spectacle to corneal plane according to the vertex distance of manifest refraction. Key words: Vector analysis;  Astigmatism;  Epi-LASIK