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Heather R. Connor, David F. Abbott, Sarah L. Hosking; Inter-eye Determination Of Visual Loss Associated With Reduced Retrobulbar Optic Nerve Diameter In Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5088.
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To determine the relationship between retrobulbar optic nerve diameter (ROND) and visual field pattern standard deviation (PSD) changes in primary open angle glaucoma (POAG) by between-eye analysis.
66 eyes of 33 normal controls (NC; mean age 56 ± 9y; range 40 - 71y) and 44 eyes of 22 POAG patients (mean age 65 ± 11y; range 44 - 87y) were included. Patients had a confirmed diagnosis of glaucoma and repeatable Humphrey 24-2 visual field defects. Optic disc and retinal nerve fibre layer analysis were performed by scanning laser tomography, optical coherence tomography and scanning laser polarimetry. 3T MRI was used to obtain T2 orbital scans; ROND was measured 5mm behind the globe (Siemens DICOM software). ROND difference between eyes was calculated as largest minus smallest for each patient, the corresponding PSD difference was then determined. ANCoVA was used to establish group differences with age as a covariate. Pearson’s product moment correlation was used to determine the relationship between parameters.
As expected, in NC there was no difference between eyes for PSD or ROND (p>0.05), and no correlation between PSD and ROND (p>0.05). Supporting the diagnosis, PSD was greater in the POAG group (p<0.01) and ROND was lower (p=0.03). For the POAG group, mean ROND was 2.5mm ± 0.5 in right eyes and 2.6mm ± 0.7 in left eyes; PSD was 7.1 ± 5.6 in the RE and 7.0 ± 5 in the LE. There was a significant trend for increasing PSD with reducing ROND (p=0.025; r =-0.48) suggesting that for each 0.1mm reduction in ROND, PSD increases by in by 4.15dB. There was no correlation between intraocular parameters and ROND.
In this study, an inter-eye reduction in ROND of 0.1mm (4%) determined by 3T MRI was associated with around a 4dB loss of visual function as measured by Humphrey 24-2 perimetry.
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