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Sarah L. Hosking, Heather R. Connor, David F. Abbott; Retrobulbar Optic Nerve Diameter in Glaucoma: Association With Brain Matter Volume. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5092.
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Reduced retrobulbar optic nerve diameter (ROND) in primary open angle glaucoma (POAG) may result from nerve fibre loss, be the consequence of greater susceptibility of thinner nerves to glaucomatous vision loss, or both. This study will determine whether POAG patients with thinner ROND also have reduced white or grey matter volume in the brain.
The sample comprised 66 eyes of 33 normal controls (NC; age 56 ± 9y) and a total of 46 eyes of 23 POAG patients (age 66 ± 11y) with repeatable Humphrey 24-2 visual field defects. Imaging of optic discs and retinal nerve fibre layer by scanning laser tomography, optical coherence tomography and scanning laser polarimetry was performed. 3T MRI provided T1 brain and T2 orbital scans. Statistical Parametric Mapping (SPM)8 software of T1 scans was used to derive total gray matter volume (GMV) and white matter volume (WMV). Localised differences between NC and POAG were also tested via Voxel Based Morphology (VBM) using SPM8. ROND was measured on T2 scans 5mm and 10mm behind the globe (Siemens DICOM software). ANCoVA was used to test for group differences with age as a covariate.
ROND 5mm behind the globe was 2.8 ± 0.4mm for NC, and 2.5 ±0.5mm for POAG (p=0.03). ROND 10mm behind the globe was 2.4 ± 0.3 mm for NC and 2.1 ± 0.4 mm for POAG (p=0.003). Mean GMV was 678.2 ± 54.3 ml3 in NC and 699.1 ± 60.3 ml3 in POAG (p>0.05). Mean WMV was 503.9 ± 54.3 ml3 for NC and 528.2 ± 52.2ml3 for POAG (p>0.05). No significant change in any localised area was found by VBM (p>0.05). No correlation was found between the other ocular parameters and ROND.
Despite reduced ROND in glaucoma, no reduction in total brain white or grey matter volume and no localised changes were observed. This finding may suggest that changes in the brain arise later in the disease process.
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