Clinical Outcomes Of Limbal Marking In SMILE For Moderate To High Astigmatism

Purpose: To observe the safety and effectiveness of limbal marking prior to femtosecond laser small incision lenticule extraction(SMILE);to compare the clinical outcomes of the correction for moderate to high astigmatism during SMILE with and without limbal marking;to explore the factors influencing the correction of astigmatism underwent SMILE.Methods: This prospective randomized control study included 240 unilateral eyes(157 right eyes and 83 left eyes)of 240 patients who underwent SMILE with astigmatism greater or equal to 1.0 diopter(D)between December 2017 to August 2018 in Tianjin Eye Hospital.These eyes were randomly divided into marked group(120 eyes,83 right eyes and 37 left eyes)and control group(120 eyes,74 right eyes and 46 left eyes)by random number table.The marked group was marked the horizontal axis at the 3 and 9 o'clock of limbus used methylthioninium chloride.The manifest refraction was observed 3 months after operation.Vector analysis was used to calculate the target induced astigmatism(TIA),surgically induced astigmatism(SIA),correction index(CI),success index(IOS),angle of error(AE)and magnitude of error(ME).SPSS 22.0 software was applied to analyze all the data by t test,Mann-Whitney test and Spearman correlation analysis.Results: 1.At 3-month following up,the mean residual astigmatism was-0.08±0.15 D in the marked group,which was significantly lower than-0.16±0.24 D in the control group(P=0.001).There was no significant difference in postoperative sphere,spherical equivalent and uncorrected distance visual acuity between the two groups(P>0.05).2.The correction index,index of success,angel of error(absolute value),magnitude of error in the marked group were 0.997±0.068,0.043±0.092,0.878±1.947 and-0.016±0.113,respectively.The correction index,index of success,angel of error(absolute value),magnitude of error in the control group were 0.976±0.121,0.098±0.142,1.653±3.132 and-0.054±0.235,respectively.Significant differences were found between two groups(P<0.05).The insignificant reduce in AE was seen in the marked group compared with the control group.3.The correlation analysis showed that there was a positive correlation between index of success and angel of error(absolute value)(P<0.001).Conclusions: 1.Limbal marking prior to SMILE was safe and effective for moderate to high astigmatism.2.Limbal-marking-based manual compensation can improve the predictability and accuracy in the correction of moderate to high astigmatism,and significantly reduce astigmatic undercorrection and the axial error during SMILE.3.The undercorrection of moderate to high astigmatism in SMILE was mainly caused by the axial misalignment.