3T Magnetic Resonance Imaging of the Posterior Visual Pathway in Early and Advanced Human Primary Open Angle Glaucoma

Abstract

Purpose: To determine the impact of primary open angle glaucoma (POAG) on structures of the posterior visual pathway using 3T Magnetic Resonance Imaging (MRI)

Methods: 57 normal controls (NC: mean age 58 (standard deviation) ± 12y, range 40 - 82y) and 37 POAG patients (mean age 66 ± 10y, range 44 - 87y) were included. Patients had repeatable visual field loss (Humphrey 24-2) or optic disc features consistent with the diagnosis of glaucoma. POAG patients were grouped as early (GLe) or advanced (GLa) using the AGIS grading system. MRI (3T Siemens Trio) T1, T2 and diffusion-weighted images were acquired and used to determine retrobulbar optic nerve diameter (ROND), optic radiations volume (ORV), fractional anisotropy (FA) mean diffusion (MD), radial diffusion (RD) (MRTrix software) and grey matter visual cortex volume (VCV: SPM8 software). ANCoVA was used to determine differences between groups using age and gender as covariants (SPSS20).

Results: Mean ROND 15mm behind the globe was significantly thinner in both GLe and GLa groups (NC 2.23mm ± 0.3; GLe 1.91mm ± 0.24: p=0.001; GLa 1.68 ± 0.45: p<0.001). ORV was reduced in GLa (3017.4 mm³ ± 517.9) compared to both NC (3426.1 mm³ ± 370.7: p=0.001) and GLe (3306.7 mm³ ± 301.7: p=0.048). FA was reduced in GLa (0.410 ± 0.023) compared to NC (0.448 ± 0.023: p<0.001) and GLe (0.439 ± 0.021: p<0.01) while RD was increased in GLa (459.34µm²/sec ± 45.72) compared to NC (417.78 µm²/sec ± 28.87: p<0.01) and GLe (528.20µm²/sec ± 22.54: p=0.05). There was no difference in VCV between groups.

Conclusions: Advanced glaucoma patients show reduced FA and increased RD in the optic radiations suggesting a loss of axonal integrity associated with glaucoma. ROND was thinner in early and advanced glaucoma patients although ORV was reduced only in the advanced group and there was no difference in VCV between any of the groups suggesting that changes in the posterior visual pathway associated with glaucoma lag anterior change.

Keywords: 550 imaging/image analysis: clinical • 629 optic nerve • 755 visual cortex