Sources of longitudinal variability in optical coherence tomography nerve-fibre layer measurements.
OBJECTIVE
The purpose of this study was to compare the day-to-day reproducibility of optical coherence tomography (OCT; StratusOCT, Carl Zeiss Meditec, Dublin, CA) measurements of retinal nerve-fibre layer (RNFL) measurements at time points 1 year apart.


METHODS
One eye in each of 11 healthy subjects was examined using the StratusOCT fast RNFL scan protocol. Three fast RNFL scans with signal strength > or =7 were obtained on each of 3 days within a month. This protocol was repeated after 12 months. A linear mixed effects model fitted to the nested data was used to compute the variance components.


RESULTS
The square root of the variance component that was attributed to the differences between subjects was 7.17 microm in 2005 and 7.28 microm in 2006. The square roots of the variance component due to differences between days within a single subject were 1.95 microm and 1.50 microm, respectively, and for within day within a single subject were 2.51 microm and 2.55 microm, respectively. There were no statistically significant differences for any variance component between the two testing occasions.


CONCLUSIONS
Measurement error variance remains similar from year to year. Day and scan variance component values obtained in a cohort study may be safely applied for prediction of long-term reproducibility.
UPMC Eye Center, Ophthalmology and Visual Science Research Center, Eye and Ear Institute, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
L
L
Kagemann
T
T
Mumcuoglu
G
G
Wollstein
R
R
Bilonick
H
H
Ishikawa
K A
KA
Townsend
M
M
Gabriele
J G
JG
Fujimoto
J S
JS
Schuman
D000328:Adult; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015203:Reproducibility of Results; D012160:Retina / Q000033:anatomy & histology*; D013995:Time; D041623:Tomography, Optical Coherence / Q000379:methods / Q000592:standards*