Abstract
Purpose: :
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.
Methods: :
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.
Results: :
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).
Conclusions: :
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.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic nerve