PURPOSE: To evaluate the reproducibility of a scanning laser polarimeter, the Nerve Fiber Analyzer II (NFA II, Laser Diagnostic Technologies, San Diego, CA, U.S.A.). METHODS: Five independent retardation maps of the peripapillary retina of five normal eyes were acquired by three experienced operators (including V.S.G.) on each of three separate days for a total of 45 retardation maps per patient. Two methods of image processing, one using a baseline image and another using the individual scans, were used to compare the reproducibility of three summary measures, average retardation, integral, and retardation ratio. RESULTS: The average standard deviation (and its 95% confidence interval) of average retardation within a 10-pixel-width-band of the 9 baseline images was 0.43 degree (0.36-0.51 degree) with a mean coefficient of variation of 4.2% (3.8-4.5%). In a random effects model, each of the three retinal nerve fiber layer (RNFL) summary measures varied significantly by patient (p < 0.016), but not by operator (p > 0.19), or operator by patient interaction (p > 0.524). In addition, there was small, but statistically significant day-by-operator-within-patient (intraobserver) variation in the random effects model. CONCLUSIONS: These results suggest that the NFA II provides reproducible measurements and that, on average, measurements obtained by separate operators on different days are similar.
PURPOSE: To evaluate the reproducibility of a scanning laser polarimeter, the Nerve Fiber Analyzer II (NFA II, Laser Diagnostic Technologies, San Diego, CA, U.S.A.). METHODS: Five independent retardation maps of the peripapillary retina of five normal eyes were acquired by three experienced operators (including V.S.G.) on each of three separate days for a total of 45 retardation maps per patient. Two methods of image processing, one using a baseline image and another using the individual scans, were used to compare the reproducibility of three summary measures, average retardation, integral, and retardation ratio. RESULTS: The average standard deviation (and its 95% confidence interval) of average retardation within a 10-pixel-width-band of the 9 baseline images was 0.43 degree (0.36-0.51 degree) with a mean coefficient of variation of 4.2% (3.8-4.5%). In a random effects model, each of the three retinal nerve fiber layer (RNFL) summary measures varied significantly by patient (p < 0.016), but not by operator (p > 0.19), or operator by patient interaction (p > 0.524). In addition, there was small, but statistically significant day-by-operator-within-patient (intraobserver) variation in the random effects model. CONCLUSIONS: These results suggest that the NFA II provides reproducible measurements and that, on average, measurements obtained by separate operators on different days are similar.