title: Lens thickness assessment: anterior segment optical coherence tomography versus A-scan ultrasonography.
abstract: OBJECTIVE
  To assess lens thickness measurements with anterior segment-optical coherence tomography (AS-OCT) in comparison with A-scan ultrasonography (A-scan US).
  
  
  METHODS
  There were 218 adult subjects (218 eyes) aged 59.2±9.2y enrolled in this prospective cross-sectional study. Forty-three eyes had open angles and 175 eyes had narrow angles. Routine ophthalmic exam was performed and nuclear opacity was graded using the Lens Opacities Classification System III (LOCS III). Lens thickness was measured by AS-OCT (Visante OCT, Carl Zeiss Meditec, Dublin, CA, USA). The highest quality image was selected for each eye and lens thickness was calculated using ImageJ software. Lens thickness was also measured by A-scan US.
  
  
  RESULTS
  Interclass correlations showed a value of 99.7% for intra-visit measurements and 95.3% for inter-visit measurements. The mean lens thickness measured by AS-OCT was not significantly different from that of A-scan US (4.861±0.404 vs 4.866±0.351 mm, P=0.74). Lens thickness values obtained from the two instruments were highly correlated overall (Pearson correlation coefficient=0.81, P<0.001), and in all LOCS III specific subgroups except in grade 5 of nuclear opacity. Bland-Altman analysis revealed a 95% limit of agreement from -0.45 to 0.46 mm. Lens thickness difference between the two instruments became smaller as the lens thickness increased and AS-OCT yielded smaller values than A-scan US in thicker lens (β=-0.29, P<0.001).
  
  
  CONCLUSIONS
  AS-OCT-derived lens thickness measurement is valid and comparable to the results obtained by A-scan US. It can be used as a reliable noncontact method for measuring lens thickness in adults with or without significant cataract.
authors.affiliation: Tehran University of Medical Science, Farabi Eye Hospital, Tehran 13336, Iran.
authors.forename: Nikoo
authors.initials: N
authors.lastname: Hamzeh
authors.affiliation: Tehran University of Medical Science, Farabi Eye Hospital, Tehran 13336, Iran ; Koret Vision Center, San Francisco Medical School, University of California, San Francisco, CA 94143, USA.
authors.forename: Sasan
authors.initials: S
authors.lastname: Moghimi
authors.affiliation: Tehran University of Medical Science, Farabi Eye Hospital, Tehran 13336, Iran.
authors.forename: Golshan
authors.initials: G
authors.lastname: Latifi
authors.affiliation: Tehran University of Medical Science, Farabi Eye Hospital, Tehran 13336, Iran.
authors.forename: Massood
authors.initials: M
authors.lastname: Mohammadi
authors.affiliation: Tehran University of Medical Science, Farabi Eye Hospital, Tehran 13336, Iran.
authors.forename: Nassim
authors.initials: N
authors.lastname: Khatibi
authors.affiliation: Koret Vision Center, San Francisco Medical School, University of California, San Francisco, CA 94143, USA.
authors.forename: Shan C
authors.initials: SC
authors.lastname: Lin
keywords: A-scan ultrasonography; anterior segment-optical coherence tomography; biometry; cataract; lens thickness