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F. T. Li, F. A. Medeiros, D. Ng, L. M. Alencar, L. M. Zangwill, R. N. Weinreb; Long-Term Variability of Stratus OCT Retinal Nerve Fiber Layer, Optic Nerve Head and Macular Thickness Measurements. Invest. Ophthalmol. Vis. Sci. 2007;48(13):521.
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To evaluate the long-term variability of optical coherence tomography retinal nerve fiber layer (RNFL), optic nerve head (ONH) and macular thickness measurements in a cohort of stable glaucoma suspects in which multiple tests were acquired over several years of follow-up.
The study enrolled a cohort of untreated glaucoma suspects from the Diagnostic Innovations in Glaucoma Study (DIGS) who did not develop any evidence of visual field damage or change in the appearance of the optic nerve (as evaluated by stereophotographs) during an average follow-up of 9.1 ± 3.1 years. Subjects underwent ocular imaging with the commercially available Stratus OCT (Carl-Zeiss Meditec, Dublin, CA) using the Fast Protocol for RNFL, ONH and macular thickness. Subjects underwent repeated testing at approximately 12 month intervals during their follow-up. For each scanning protocol, 76 exams were obtained in 26 individuals during an average Stratus OCT follow-up time of 28 ± 8.81 months (range: 12 to 48 months). Due to the relatively recent introduction of the Stratus OCT, the follow-up time with this instrument was considerably lower than the total follow-up time as part of the DIGS study. A random effects analysis of variance model was used to estimate intraclass correlation coefficients (ICCs) and intervisit standard deviations. Long-term test-retest variability was calculated as 1.96 times the intervisit standard deviation. One eye from each subject was randomly selected for statistical analysis.
For RNFL thickness parameters, ICCs ranged from 0.51 to 0.91. The parameter with highest ICC was average thickness (0.91, 95% CI: 0.83 - 0.95). Long-term test-retest variability for the average thickness parameter was 5.28µm (4.33µm - 6.43µm). For ONH parameters, ICCs ranged from 0.64 to 0.96. The parameter with highest ICC was cup area (0.96; 95% CI: 0.92 - 0.98). For macular thickness parameters, ICCs ranged from 0.67 to 0.88. The parameter with highest ICC was superior inner macular thickness (0.88, 95% CI: 0.78 - 0.94).
In general, Stratus OCT parameters showed good to moderate long-term reproducibility in glaucoma suspects. However, important differences were observed among the different parameters from each one of the scanning protocols. These differences should be taken into account when considering Stratus OCT for long-term longitudinal evaluation of patients suspected of having glaucoma.
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