title: Comparison axial length measurements from three biometric instruments in high myopia.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Shanxi Eye Hospital, Taiyuan 030002, Shanxi Province, China; Department of Ophthalmology, the Sixth People's Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 200233, China.
authors.forename: Xiao-Gang
authors.initials: XG
authors.lastname: Wang
authors.affiliation: The First Hospital of Shanxi Medical University, Taiyuan 030001, Shanxi Province, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Dong
authors.affiliation: Department of Ophthalmology, the Sixth People's Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 200233, China.
authors.forename: Yu-Lan
authors.initials: YL
authors.lastname: Pu
authors.affiliation: Department of Ophthalmology, the Sixth People's Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 200233, China.
authors.forename: Hui-Jun
authors.initials: HJ
authors.lastname: Liu
authors.affiliation: Department of Ophthalmology, the Sixth People's Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 200233, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wu
keywords: axial length; biometry; high myopia; intraocular lens; repeatability