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Lauren A. Forbes, Jean-Claude Mwanza, Hanna Kim, Joshua Warren, Richard K Lee, Donald L Budenz; Residual and Dynamic Range of Retinal Nerve Fiber Layer Thickness in Glaucoma: Comparison of Three OCT Devices. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4559. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate and compare the amounts of relative visual field (VF) sensitivity at which retinal nerve fiber layer (RNFL) thinning is no longer significant and at which RNFL completely stops thinning (change points), the dynamic range of RNFL thickness, and the number of steps from normal to RNFL floor among 3 OCT devices in moderate to severe glaucoma.
58 glaucomatous patients prospectively underwent RNFL thickness measurement with Cirrus, Spectralis, and RTVue and VF testing with Hymphrey Field Analyzer. VF and RNFL of healthy subjects (60 for Cirrus and Spectralis, 55 for RTVue) were also included. The change points and corresponding RNFL thicknesses were estimated with simple liner regression (SLR) and Bayesian change point (BCP) analyses. The dynamic range and number of steps to RNFL floor were determined for each device.
The SLR method estimated the average change points and RNFL thickness at -10.4 dB and 57.1 µm (Cirrus), -13.9 dB and 48.0 µm (Spectralis), and -19.2 dB and 60.4 µm (RTVue). Estimates of the average change point and corresponding RNFL thickness from the BCP analysis were -22.2 dB and 57.0 µm (Cirrus), -25.3 dB and 49.2 µm (Spectralis), and -24.6 dB and 64.7 µm (RTVue). Residual thickness estimates on RTVue tended to be thicker than those on Cirrus and Spectralis, whereas Spectralis measurements were thinner than those from Cirrus. In general, RNFL reached the change point earlier in the SLR than BCP method. There were no significant differences between post-BCP and post-SLR residual layer thicknesses on all 3 devices (all P>0.05), but post-BCP relative VF sensitivities were worse than post-SLR sensitivities (P<0.05). The dynamic range of global RNFL and the number of steps to RNFL floor estimated by the 2 methods were similar on each device. The RNFL dynamic ranges from BCP and SLR were wider on Spectralis (52.9 and 56.5 µm) than on Cirrus (36.1 and 36.6 µm) and RTVue (41.0 and 38.5 µm); the corresponding number of steps to RNFL floor did not vary much among devices (9.3 and 9.4 on Cirrus, 10.7 and 11.5 on Spectralis, and 9.5 and 8.9 on RTVue).
The amount of relative VF sensitivity at which average RNFL reaches the floor, the residual layer thickness, and RNFL dynamic range differ among the 3 devices. However, the number of steps to the RNFL floor is similar among them.
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