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G. Michelson, T. Engelhorn, S. Haider, A. Dörfler; Fiber-Tracking of Fourth Neuron in Glaucoma Patients Using High-Field MRI. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4616.
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Glaucomatous optic atrophy may be associated with a degeneration of the fourth neuron. Fiber-tracking using diffusion tensor imaging (DTI) may represent a sensitive non-invasive technique for early diagnosis of pathologic alterations of the visual pathway. The aim of our study was to evaluate the integrity of the visual pathway (axons of fourth neuron) in patients with glaucoma using DTI.
Complete MRI of the brain was performed in eleven glaucomatous patients with a long lasting glaucoma harbouring visual field defects (mean age 53±12). The visual field of OD and OS was estimated by the Frequency Doubling Technique (FDT). In addition to conventional sequences (T1, T2), an isotropic 3D-FLAIR and a T2*-sequence were acquired to evaluate location and extent of microvascular lesions of the brain (white matter lesions), classified according a rating scale with a score of 0 indicating no microvascular lesions, and a score of 1-3 indicating presence of microvascular lesions, respectively. Diffusion tensor imaging (DTI) was performed using an EPI single-shot sequence covering the entire brain. Subsequently, fiber tract extraction was achieved using dedicated software to directionally depict white matter junctions from the lateral geniculate body towards the occipital cortex. Fiber tracts were outlined and the data were compared to a control group of age-matched healthy volunteers whereby atrophy was expressed as percentage compared to controls.
In 9 of the 11 patients with glaucomatous optic nerve atrophy we found signs of cerebral microvascular lesions (in 4 patients score 1, in 5 patients score 2). In 5 of the 11 patients (45%) DTI revealed a degeneration of the fourth neuron. In these patients, the visual pathway was significantly thinner (atrophic): volumetric quantification revealed a reduction to 68±14% compared to controls. One patient presented microangiopathic lesions exclusively within the left thinned visual pathway. Two patients with large ischemic lesions (strokes) in the occipital brain showed a degenerated visual pathway and a glaucomatous optic nerve atrophy.
Using diffusion tensor imaging visualisation of the axons of the fourth neuron could be reliably performed in all patients with glaucomatous optic nerve atrophy showing degeneration of the fourth neuron in up to 45%. These preliminary data suggest that fiber-tracking using DTI may be a sensitive non-invasive technique for early visualisation of degenerations of the fourth neuron associated with glaucomatous optic nerve atrophy.
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