Reproducibility of scanning laser polarimetry (GDx) of peripapillary retinal nerve fiber layer thickness in normal subjects

Purpose: To assess the reproducibility of measurement of retinal nerve fibe r layer (RNFL) thickness among subjects using the GDx Nerve Fiber Analyzer (NFA). Methods: One eye of each of five young and healthy volunteers was im aged by three newly trained technicians (R.-H.P, K.-R.K., and S.-T.K.). Eac h volunteer was scanned six consecutive times for five independent times wi thin a I-month period. One composite image was selected out of three best i mages per session. Intra- and inter operator reproducibilities were calcula ted and the influence of placement of measurement ellipse by a single opera tor on interobserver re-producibility was also investigated. Results: Mean coefficients of variation for total integral value of RNFL were 3.67 +/-1.4 7%, 3.86 +/-2.13%, and 4.16 +/-1.97%, respectively for the three technician s. Interoperator variability was not statistically significant (P=0.075), a nd the difference was even less if a single ellipse drawn by one operator w as used in all measurements (P=0.1528) by repeated-measures analysis of var iance (ANOVA). Conclusions: The results suggest that GDx NFA may provide ac ceptable intraoperator as well as interoperator reproducibility among Asian eyes.