Comparison Of Corneal Thickness Measured By Two Kinds Of Instruments

Objective: Accurate measurement of corneal thickness is of great significance for the diagnosis of glaucoma,keratoconus and other ophthalmic diseases,as well as the parameter setting of laser in situ keratomileusis(LASIK)and small incision lenticule extraction(SMILE).Traditional ultrasond pachymeter(USP)is considered to be the gold standard for corneal thickness measurement.The purpose of this paper is to compare the differences and similarities of measurement results of Central Corneal Thickness(CCT)by Canontx-20P? non-contact tonometer and Pentacam Scheimpflug imaging system,so as to provide a basis for the accuracy of rapid,economical and simple measurement of CCT in clinical practice.Methods: A total of 184 eyes of 92 patients who underwent two types of corneal refractive surgery(LASIK or SMILE)at the Ophthalmic Refractive Center of the Second Affiliated Hospital of Anhui Medical University between March 2019 and June 2019 were collected for preoperative CCT measurement using Pentacam scheimpflug imaging system and Canontx-20P? non-contact tonometer.Based on the CCT measured by Pentacam Scheimpflug imaging system,the CCT values of the patients were divided into three groups according to the corneal thickness measurement criteria(thin,medium and thick): CCT≤510μm,510μm<CCT≤570μm and CCT>570μm.Paired t-test,Pearson correlation analysis and Bland-Altman consistency test were used for statistical analysis.Results: The CCT results of Pentacam scheimpflug imaging system and Canontx-20p? non-contact tonometer at CCT≤510μm,510μm<CCT≤570μm and CCT >570μm were(491.17±22.06)μm vs(487.77±21.66)μm,(544.27±14.23)μm vs(539.09±14.86)μm and(587.24±10.51)μm vs(580.88±9.65)μm,respectively.The results of paired t-test showed statistically significant differences(P=0.006,<0.001).The results of Pearson correlation analysis were 0.950,0.888 and 0.842 respectively,and the results showed high correlation.Bland-Altman analysis shows that within the three grouping ranges of CCT≤510μm,510μm<CCT≤570μm and CCT>570μm,the maximum absolute value difference between the two instruments was 14.32μm,18.42 um and 16.89 um respectively within the limits of agreement,and the error range was not acceptable in clinical application.Therefore,the two instruments showed poor consistency.Conclusion:1.Compared with CCT results from Pentacam scheimpflug imaging system,the Canontx-20p? non-contact tonometer was thinner than the CCT results obtained from Pentacam scheimpflug imaging system,a paired t-test was performed on corneas with different thickness ranges of CCT≤510μm,510μm<CCT≤570μm and CCT > 570μm.Pearson correlation analysis showed a high correlation between the two.Both Pentacam and the Canontx-20p? non-contact tonometer can therefore be used clinically.2.In the bland-Altman consistency analysis of CCT of each group of Pentacam scheimpflug imaging system and Canontx-20p? non-contact tonometer,although the maximum absolute difference between the three groups was greater than 10μm but less than 20μm within the limits of agreement,this was clinically unacceptable margin of error and resulted in poor consistency between the two instruments.