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Repeatability of on- and off-axis eye length measurements using the lenstar
Krystal L Schulle1, David A Berntsen
1University of Houston, College of Optometry, Houston, Texas 77204-2020, USA.
Purpose:
To determine the repeatability of eye length measurements made centrally and off-axis using a low-coherence interferometer.
Methods:
Eye length was measured (left eye) in 29 adults using the Haag-Streit Lenstar LS 900. Five measurements were made centrally, 10 degrees temporally, and 10 degrees nasally on the retina by the same examiner at two separate visits. Intervisit repeatability was assessed by plotting the difference versus the mean of each pair of measurements (bias) and calculating the 95% limits of agreement (LoA). Within-session repeatability was determined by calculating the within-subject SD (Sw) of five consecutive measurements at a visit. Because of variability noted 10 degrees nasally, the Sw was also determined on a subset of 10 subjects using five measurements at one visit 30 degrees nasally and 30 degrees temporally.
Results:
The mean ± SD age, spherical equivalent refractive error, and central axial length (at visit 1) were 24.0 ± 1.4 years, -3.46 ± 2.69 diopters, and 24.91 ± 1.10 mm, respectively. There was no significant bias for central, 10 degrees nasal, or 10 degrees temporal measurements between visits (all p > 0.09). The 95% LoA were ± 0.05 mm central, ± 0.12 mm 10 degrees nasal, and ± 0.05 mm 10 degrees temporal. The Sw (visit 1) were 0.025 mm central, 0.045 mm 10 degrees nasal, and 0.028 mm 10 degrees temporal. The Sw in the subset of subjects with 30-degree measurements were 0.023 mm (30 degrees nasal) and 0.030 mm (30 degrees temporal).
Conclusions:
Lenstar central and off-axis eye length measurements are very repeatable, although repeatability was not as good 10 degrees nasally on the retina as indicated by the larger 95% LoA between visits and larger Sw. The Sw for measurements centrally and 30 degrees off-axis were similar, suggesting that the reduced repeatability 10 degrees nasally is anatomical in nature. Despite greater variability 10 degrees nasally, Lenstar off-axis repeatability is still superior to the repeatability of on-axis ultrasonography.