Comparison between IOL MASTER 500 and MYAH with vector analysis in low and mild anterior corneal astigmatism

Purpose: Evaluate the agreement between IOL Master 500 (Carl Zeiss Meditec AG, Germany) and MYAH (Topcon EU, Visia Imaging, Japan) in measuring axial length, keratometry, and anterior corneal astigmatism. Setting: Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Ophthalmology Clinic, University of Messina, Messina, Italy. Methods: In this prospective study, 40 eyes (right eye 25, left eye 25) of 40 patients were included. Axial length (AL), ker-atometry (K1, K2), and anterior corneal astigmatism (ACA) were measured. AL, mean K (Kavg) and magnitude of ACA were compared using Bland - Altman plot analysis, parametric and nonparametric statistical analysis. The difference vector and angle of error of the ACA measured by the two devices were evaluated by vector analysis using polar diagrams. Results: Mean and standard deviation with IOL Master and with MYAH device was for AL 24.25 +/- 1.22 mm and 24.25 +/- 1.22 mm (p = .99), for Kavg 42.75 +/- 1.53 D and 42.85 +/- 1.52 D (p = .78), for Magnitude of ACA 1.00 +/- 0.58 D and 0.89 +/- 0.56 D (p = .38) respectively. High correlations were found for AL (R-2 = 0.999), Kavg (R-2 = 0.996), and ACA Magnitude (R-2 = 0.889). Bland-Altman analysis of the two devices found high agreement and absence of propor-tional bias (MYAH-IOL MASTER) were found between the two assessments for AL (bias = -0.0005 mm, p = .93), Kavg (bias = 0.0955 D, p = .76) and ACA (bias = 0.11 D, p = .41). Limit of agreement (upper/lower LoA, 95%CI) were respectively +0.057/ -0.058 mm for AL, + 0.29/-0.09 D for Kavg and +0.49/-0.27 D for ACA. No statistical difference was found between the x-component and y-component of the ACA vector (p > .01), the difference vector (IOL MASTER-MYAH) was +0.14 D axis 159 with an absolute mean angle of error of 7.2 +/- 7.5 degree. Conclusions: The instruments appear to be interchangeable for measurements of AL, keratometry, and magnitude of ACA with high agreement between the two devices. Also, in the presence of low astigmatism, the two instruments give the same results in terms of ACA.