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Editors Selection IGR 15-3

High-Speed MRI as Biomarker for Axonal Loss

Comment by Yeni Yucel on:

24162 Retrobulbar optic nerve diameter measured by high-speed magnetic resonance imaging as a biomarker for axonal loss in glaucomatous optic atrophy, Lagrèze WA; Gaggl M; Weigel M et al., Investigative Ophthalmology and Visual Science, 2009; 50: 4223-4228

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Lagrèze et al. (1124) discuss a novel magnetic resonance imaging protocol for quantifying the optic nerve diameter (OND) as a measure of axonal loss in the optic nerve. The study shows significant correlation between optic nerve diameter at the orbital apex (15 mm behind the eye) and RNFL parameters measured using GDx, OCT and HRT. In fact, the relationship between OND and optic nerve fiber number in human glaucoma and in experimental monkey model of glaucoma is well established. The study included nine normal patients, and 38 glaucoma patients (16 with preperimetric glaucoma, 11 with MD of < 0 dB and 11 with MD > 10 dB). OND measurements were performed at five, ten and 15 mm behind the eye measured with HASTE protocol. Interestingly, only OND measurements performed at 15 mm from the eye showed significant correlation with RNFL parameters. It would be important to know whether this difference in OND at various distances from the eye is due to difference in axon number or difference in glial reaction. I believe that in this emerging area of neuroimaging research in glaucoma, an adequate description of the technique including total scanning time patients' characteristics including the gender, age and IOP should be provided in detail. Age can be confounding factor for neuroimaging parameters since optic nerve fiber loss with age has been previously described. In this study, glaucoma patients with glaucoma appear older than normal patients. Statistical comparison of neuroimaging parameters between normal and glaucoma groups should be disclosed. Correlation analysis should be also performed in the group of glaucoma patients. This article contributes to the potential use of noninvasive neuroimaging in the assessment anterior visual pathways. More studies are needed to develop a normative database based on patients with varying ages in both genders. Structural neuroimaging shows great potential to be specific biomarkers for neural degeneration in the optic nerve1 and in the lateral geniculate nucleus² in glaucoma.

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