Comparison axial length measurements from three biometric instruments in high myopia.

AIM: To compare the axial lengths (ALs) measured with Lenstar, IOLMaster and A-scan contact ultrasound (Ultrasound) in normal and high myopia (HM). METHODS: Eighty-four normal eyes and 49 HM eyes were included. Three consecutive measurements were performed on each eye in the following order: Lenstar, IOLMaster, and Ultrasound. The repeatabilities of the AL measurements for each instrument were assessed by calculating the pooled coefficients of variation (CVs) of 18 eyes in each group. Comparisons between the HM and normal groups were made with independent sample t-tests. The inter-device agreements were evaluated with Bland-Altman analyses and paired two-tailed t-tests. RESULTS: For normal group, the CVs of the AL measurements taken with the Lenstar, IOLMaster and Ultrasound were 0.001%, 0.01% and 0.14%, respectively. The corresponding CVs for the HM group were 0.005%, 0.02% and 0.15%, respectively. There was significant difference between the Lenstar and the IOLMaster in normal group (P=0.031) but not in HM group (P=0.100). In the two groups, the Lenstar and the IOLMaster produced higher values than did the Ultrasound (all P<0.001). All three instruments exhibited good agreement in terms of AL values. For the intraocular lens (IOL) power calculation using SRK II formula, the Lenstar and the IOLMaster showed 0.5 D higher than Ultrasound in both groups (all P<0.001). No significant difference existed between the Lenstar and the IOLMaster for the IOL power calculation in both normal (P=0.474) and HM group (P=0.103). CONCLUSION: The three devices exhibited excellent intra-visit repeatabilities in the AL measurements. The AL and IOL power difference between partial coherence interferometry and ultrasound instruments should be noticed.