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@#AIM:To compare the difference, correlation and consistency of the thinnest corneal thickness(TCT)in myopic patients among Sirius, Oculyzer, anterior segment optical coherence tomography(AS-OCT)and A-mode ultrasound pachymetry, in order to provide a reference for clinical applications.<p>METHODS: TCT was measured in 81 patients(162 eyes)treated between March and April, 2016 using Sirius, Oculyzer, AS-OCT and A-mode ultrasound pachymetry before femtosecond LASIK, and then the values were statistically analyzed.<p>RESULTS: TCT measured by A-mode ultrasound pachymetry, Sirius, Oculyzerand AS-OCT were respectively(537.91±24.12)μm,(538.12±22.64)μm,(538.20±23.74)μm,(527.04±23.11)μm(<i>P</i><0.01). There was a significant difference in TCT measurements among the four measurements. The results of AS-OCT were significantly smaller than those of the other three methods. There was no statistical difference among A-mode ultrasound pachymetry, Sirius and Oculyzer.Pearson correlation coefficient of measured value by the four measurements were more than 0.9(<i>r</i>=0.920, 0.914, 0.951, 0.908, 0.929, 0.919, <i>P</i><0.001), which means there were highly correlation between each other. The 95% <i>CI</i> of the consistency interval of A-mode ultrasound pachymetry and Sirius, A-mode ultrasound pachymetry and Oculyzer, A-mode ultrasound pachymetry and AS-OCT were(-18.77-18.33)μm,(-19.79-19.19)μm,(-3.79-25.53)μm, respectively. The Bland-Altman Plots demonstrates relatively good consistency between A-mode ultrasound pachymetry and the other three methods.<p>CONCLUSION:The TCT measured by AS-OCT were thinner than that measured by A-mode ultrasound pachymetry. There were a high correlation and consistency of the thinnest corneal thickness in myopic patients among Sirius, Oculyzer, AS-OCT and A-mode ultrasound pachymetry. The TCT measured by the four measurements can be referenced but not replaced since the 95% of the consistency intervals were wide.
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AIM:To compare CASIA SS-1000 and Sirius OCT sweep anterior segment analyzer instrument for measuring normal corneal vertex thickness (CCT) and the thinnest corneal thickness (TCT) results the difference,correlation and consistency,and provide a theoretical basis for clinical application.METHODS:This was a prospective study.A total of 34 normal subjects were collected.The subjects were measured by the same skilled operator.The SS-1000 OCT was first used,and then the corneal thickness was measured repeatedly by Sirius anterior segment analyzer.Paired t test and Bland-Altman were used to evaluate the consistency of corneal apex and corneal thinnest point between SS-1000 OCT and Sirius anterior segment analyzer.RESULTS:The mean corneal apex measured by SS-1000 OCT and Sirius corneal topography were 517.62± 25.29μm and 518.47±27.23μm CCT,respectively.The thinnest points of SS-1000 OCT and Sirius anterior segment analyzer CCT were 513.53±25.06μ m and 515.32± 26.69μm,respectively.Paired t test showed that the difference on corneal thickness of vertex was not statistically significant (P＞0.05),but the thinnest corneal thickness was statistically significant (P＜ 0.05).Pearson analysis of the two devices,the correlation is 0.969,0.965.The results of 95％ consistency limiting analysis on the corneal vertex thickness by Bland-Altman was (-14.22μm,12.52μm),that of the thinnest corneal thickness was (-15.61μm,12.03μm),4％ (3/68) was out of the 95％ consistency limiting,but the thinnest corneal thickness was of a little larger differences.CONCLUSION:SS-1000 OCT measurement of CCT and Sirius anterior segment analyzer is highly consistent,in clinical work can be considered alternative,but the thinnest point of the cornea can not be replaced each other.
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AIM:To discuss the related factors that affected the stability of posterior corneal surface after laser in situ keratomileusis ( LASIK) . METHODS:About 64 patients (64 eyes) were enrolled. The correlation among the changes in posterior corneal surface 6 month after LASIK, surgery method, corneal flap thickness ( FT ) , ablation thickness ( AT ) , postoperative residual corneal stroma thickness ( RCST ) , preoperative thinnest corneal thickness ( CT ) , flap thickness/preoperative thinnest corneal thickness ( FT/CT ) , ablation thickness/preoperative thinnest corneal thickness ( AT/CT) , postoperative residual corneal stroma thickness/preoperative thinnest corneal thickness ( RCST/CT) , anterior and posterior preoperative corneal height, the difference of the forward shift in posterior corneal surface ( diff value ) of preoperative and preoperative intraocular pressure were analyzed. RESULTS: The changes of diff value between preoperative and postoperative were related with diopter (r=0.419, P=0.014), AT (r=0.394, P=0.023), AT/CT (r=0.501, P=0.004), Diff value of preoperative (r=0.501, P=0. 004), RCST (r=-0. 385, P=0. 033) and RCST/CT (r=-0. 401, P=0. 025). The changes of height value from posterior corneal surface between preoperative and postoperative were related with diopter (r=0. 520, P=0. 002), AT (r=0.504, P=0. 003), AT/CT (r=0. 442, P=0. 013), Diff value of preoperative (r=0. 624, P=0. 000) and RCST/CT (r=-0. 394, P=0. 028). CONCLUSION: AT, RCST, AT/CT, RCST/CT and diff value of preoperative should be the key index that predicted the stability of posterior corneal surface after LASIK,the further research will give the range of safety value.
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PURPOSE: To evaluate error of corneal thickness measurement in different gazes in Orbscan topography. METHODS: Sixty eyes of 30 normal subjects were investigated using the Orbscan topography system. The central corneal thickness (Kc) and the thinnest corneal thickness (Kt) on topography map were obtained in 5 different gazes. Gaze directions were classified into center (C), nasal I (NI), nasal II (NII), temporal I (TI), and temporal II (TII), in which I means 13 degree deviation from visual axis and II means 22 degree deviation. RESULTS: Kc in right eye was 540.4+/-37.7 micro meter(mean+/-standard deviation) at central gaze (C) and 550+/-36.9 micro meter at NI ; there was no significant change, but there were in Kc at NII (563.0+/-40.5 micro meter), TI (566.5+/-32.8 micro meter), TII (595.2+/-54.5 micro meter). In addition, the same patterns were seen in left eye in Kc analysis. In contrast, Kt did not change even in 5 gaze changes. In comparison between Kc and Kt at the same gazes, there were significant differences except in central gaze (C). CONCLUSIONS: Though the gaze direction changed, the most reliable measurement for evaluation and follow up of corneal thickness is the thinnest corneal thickness (Kc) in Orbscan topography system. In case that the central corneal refractive power and thickness were needed, it is important that Orbscan topography is performed in exact central fixation.