Longitudinal Variability of Optic Disc and Retinal Nerve Fiber Layer Measurements

Abstract

To evaluate the longitudinal variability of optic disc and retinal nerve fiber layer (RNFL) measurements obtained from optical coherence tomography (OCT), scanning laser polarimetry (SLP), and confocal scanning laser ophthalmoscopy (CSLO). Forty-five normal and 43 glaucomatous eyes of 88 subjects were analyzed in this longitudinal study. RNFL thickness was measured by OCT (StatusOCT; Carl Zeiss Meditec, Dublin, CA) and SLP (GDx VCC; Carl Zeiss Meditec). Neuroretinal rim area was measured by CSLO (HRT 3; Heidelberg Engineering, GmbH, Dossenheim, Germany). Three separate measurements taken over an average period of 8.8 +/- 1.2 months were used to evaluate measurement variability. Reproducibility coefficient, coefficient of variation, intraclass correlation coefficient (ICC), and sensitivity to change [(97.5 percentile value - 2.5 percentile value)/2 x within-subject standard deviation (Sw)] of the global measures were calculated. The association between RNFL and rim area measurement variability and visual field MD (mean deviation) was evaluated with regression analysis. Low variability was found for global and sectorial rim area and RNFL measurements. The reproducibility coefficient, ICC, and sensitivity to change for OCT average RNFL thickness, GDx VCC TSNIT average, and HRT global rim area were 11.7 microm (95% confidence interval [CI]: 10.5-12.9 microm), 0.97 (0.96-0.98), 10.2 (9.2-11.4); 4.7 microm (4.2-5.1 microm), 0.98 (0.97-0.99), 11.3 (10.2-12.6); and 0.22 mm(2) (0.19-0.24 mm(2)), 0.97 (0.95-0.98), 9.3 (8.4-10.4), respectively. No association was found between OCT (r = 0.010 [95% CI: -0.200-0.219], P = 0.924) and SLP (r = -0.034 [95% CI: -0.241-0.177], P = 0.756) RNFL thickness variances and visual field MD. The association between CSLO rim area variance and visual field MD became insignificant after adjustment for reference height variance. Longitudinal RNFL and neuroretinal rim measurements obtained with OCT, SLP, and CSLO have low variability. As the measurement variability does not change with the severity of glaucoma, these parameters are useful for assessment of glaucoma progression.