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S. T. Chang, J. Xu, K. M. Trinkaus, S.-K. Song, E. M. Barnett; 3-T Diffusion Tensor Imaging of Optic Nerve Changes in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2711.
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(1) To compare the diffusion tensor imaging (DTI) indices mean diffusivity (MD), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) between adult subjects with and without glaucoma. (2) To correlate these DTI indices with the Heidelberg Retinal Tomograph (HRT) indices rim area (RA) and retinal nerve fiber layer thickness (RNFLT) and also with the clinical stage of glaucomatous visual field damage.
Subjects were recruited from the Washington University Eye Center. Subjects were enrolled into one of two groups ("glaucoma" or "normal") based on an established diagnosis which was confirmed through a complete eye exam. MR images were acquired for all subjects using a 4-element phased array custom-fabricated receiver coil on a 3T scanner (Trio, Siemens). Oblique transaxial diffusion weighted images were acquired (FOV 166x72 mm, matrix 128x56, and TR/TE ~8000/103 ms) on nine interleaved gapless slices of 1.3 mm thick, using a previously described reduced field of view (rFOV). A HRT was prospectively performed for the majority of the subjects within 9 months of their DTI. Every eye was given a clinical stage based on the Modified Bascom Palmer Glaucoma Staging System. A repeated measures linear model was used to compare the DTI indices between the two groups and also to correlate these indices with RA, RNFLT, and clinical stage of glaucoma.
All four of the DTI indices were statistically different between glaucoma and normal subjects. Log mean MD for the glaucoma eyes was significantly greater compared to normal eyes (1.33 vs. 0.91 µm2/ms, p=0.0002) while log mean FA was significantly lower for the glaucoma versus normal eyes (0.21 vs. 0.44, p < 0.0001). Axial (1.70 vs 1.43 µm2/ms, p=0.036) and radial (1.24 vs. 0.71 µm2/ms, p < 0.0001) diffusivities were significantly greater in the glaucoma versus normal eyes. There were significant inverse correlations between RA and MD, RA and RD, RA and AD, RNFLT and MD, and RNFLT and RD. There were significant direct correlations between RA and FA, and RNFLT and FA. MD, RD, and AD increased while FA decreased significantly as the clinical stage of glaucoma worsened.
DTI can distinguish between optic nerves affected by glaucoma and unaffected controls. MD, FA, and RD are strongly correlated with RA and RNFLT while there was a weaker relationship between AD and these HRT indices. Similarly, MD, FA, and RD strongly correlated while AD had a weaker dependence on the clinical stage of glaucoma.
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