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Carlo Nucci, Alessio Martucci, Raffaele Mancino, Francesca Bolacchi, Roberto Floris, Giovanni Simonetti, Luciano Cerulli, Francesco G. Garaci; Differences Between Proximal And Distal Intraorbital Optic Nerve Diffusion Tensor-MRI Indexes In Glaucoma Patients. Invest. Ophthalmol. Vis. Sci. 2012;53(14):734.
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To analyse, in vivo, in glaucoma patients, the diffusion tensor magnetic resonance imaging (DT-MRI) properties of the intraorbital optic nerve at two different levels: proximal and distal to the optic nerve head.
The study was approved by the review board of University Hospital Tor Vergata. All participants provided informed consent. Twenty-four patients with primary open-angle glaucoma were examined. The categorization into early and severe glaucoma was performed by Hodapp’s classification. Fifteen healthy individuals served as control subjects. DT-MR imaging was performed with a 3-Tesla-MR unit. Regions of interest (ROIs) analysis was performed on each intraorbital optic nerve at 4 mm (proximal) and 20 mm (distal) from the optic nerve head. The ROIs were electronically superimposed on the DTI maps to obtain Mean Diffusivity (MD) and Fractional Anisotropy (FA) values.
At early glaucoma stages, MD and FA values of the proximal segment were significantly different from those observed in controls (MD: 1550±180 vs 860±150, p=0.0035; FA: 515±50 vs 390±43, p=0.011), whereas the distal part showed a slight but not statistically significant increase in the MD and a statistically significant decrease in the FA (562±60 vs 400±53, p=0.025). At severe glaucoma stages both the proximal and the distal portions of the optic nerve showed altered MD values with respect to control subjects (860±150 vs 1900±220, p=0.003 and 900±170 vs 1850±280, p=0.002), and even more a statistically significant decrease of FA with respect to controls (515±50 vs 260±34, p=0.001 and 562±60 vs 290±58, p=0.001).
Our results indicate that according to DT-MRI intraorbital optic nerve degeneration is a complex biological process that affects differently the proximal and the distal segments of the intraorbital optic nerve at early disease stages.
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