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Background
Corvis ST corneal biomechanical analyzer (Corvis ST) can offer corneal biomechanical parameters, intraocular pressure (IOP) and central corneal thickness (CCT), and measured IOP value was corrected based on CCT and biomechanical factors.Corvis ST is applied abroad, but the study on its accuracy is few in China.
Objective
This diagnostic trial was to evaluate the accuracy of Corvis ST for CCT and IOP measurement in myopic population.
Methods
Fifty-six eyes from 56 myopic patients were prospective recruited in Visual Science and Optometry Center of Guangxi from November to December in 2012.IOP was measured by using Corvis ST and Goldmann applanation tonometer (GAT), and CCT was measured by Corvis ST and A type ultrasonic pachymetry.The CCT difference between Corvis ST and A type ultrasonic pachymetry as well as IOP between Corvis ST and GAT were compared by using paired-t test, and agreements of measured outcomes were analyzed by Bland-Altman method.This study was approved by the Ethic Committee of People’s Hospital of Guangxi and written informed consent was obtained from all subjects.
Results
The CCT from Corvis ST was (539.82±19.79)μm, which was significantly higher than (535.34±19.41)μm from A type ultrasonic pachymetry (t=4.19, P<0.001). Bland-Altman analysis revealed that the CCT measured by Corvis ST was 4.5 μm higher than that of A type ultrasonic pachymetry, with the 95% limit of agreement ranged from -11.2 to 20.2 μm, and 7.1% (4/56) of points were located at the outside of the 95% confidence interval.The IOP measured by Corvis ST and GAT were (15.75±1.60) mmHg and (16.23±2.40) mmHg, respectively, showing statistically significant difference between the two methods (t=2.15, P=0.04). Bland-Altman analysis revealed that the IOP measurement of Corvis ST was 0.5 mmHg lower than that of GAT, with the 95% limit of agreement ranged from -3.8 to 2.8 mmHg, and 3.57%(2/56) of points were located at the outside of the 95% confidence interval.
Conclusions
CCT obtained by Corvis ST is higher than that by A type ultrasonic pachymetry with poor agreement between these two outcomes, and the two methods cannot replace each other clinically in myopic eyes.IOP value from Corvis ST is slightly lower than that from GAT, showing a good agreement between these two outcomes.The IOP value of Corvis ST shows satisfactory accuracy.