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Georg Michelson, Simone Waerntges, Tobias Engelhorn, Ahmed El-Rafei, Joachim Hornegger, Arnd Dörfler; DT-MRI Measures Reflecting Axonal Integrity and Myelin Damage in the Optic Radiation Correlate with the Retinal Nerve Fiber Layer Thickness in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3961.
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In glaucoma damage of retinal ganglion cells may continue to the linked optic radiations (OR). This damage may concern the axonal integrity as well as demyelination or glia cell impairment. This study investigated measures of axonal integrity, i.e. fractional anisotropy (FA), and demyelination, i.e. radial diffusivity (RD), in the optic radiation of glaucoma patients. The results were correlated with the homonymous retinal nerve fiber layer thickness (RNFL).
Fourteen control subjects (mean age, 52.0±11.7 years) were age-adjusted to 12 patients with normal tension glaucoma (NTG, mean age, 58.3±9.5 years; p=0.157) and 18 patients with primary open angle glaucoma (POAG, mean age, 55.7±7.3 years; p=0.296). The control subjects had eye diseases without neuronal participation. All subjects underwent magnetic resonance (MR) tomography-based diffusion tensor imaging (DTI) of the optic radiation and eye examination by the Spectralis optical coherence tomography. MR images did not show cerebral space occupying lesions along the visual pathway. The optic radiations in the DTI were outlined semi-automatically and the mean values of FA and RD of both OR’s were measured. The homonymous RNFL thickness corresponding to the respective OR was calculated.
If corrected for age, gender, and diagnosis groups (control, NTG, POAG) partial correlation analysis disclosed a correlation between FA and RNFL thickness (right OR: r=0.386, p=0.013; left OR: r=0.399, p=0.010). RD correlated with the RNFL thickness, too (right OR: r=-0.350, p=0.025; left OR: r=-0.478, p=0.002).
In glaucoma DTI-derived parameters of axonal integrity and demyelination or glia cell impairment of the optic radiation (4th neuron) are suggested to change with decreasing retinal nerve fiber layer thickness (3rd neuron), i.e. with increasing glaucoma severity.
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