Imaging the eye as a window to the brain. Better correlation with white matter damage

Epub: Young et al. Loss of retinal nerve fibre layer axons indicates white but not grey matter damage in early multiple sclerosis. Eur J Neurol. 2013 Jan 31. doi: 10.1111/ene.12070. 

BACKGROUND AND PURPOSE: Optical coherence tomography (OCT) has shown thinning of the retinal nerve fibre layer (RNFL) and total macular volume (TMV) in multiple sclerosis (MS) patients. Measures of retinal atrophy are associated with the brain parenchymal fraction (BPF) assessed by magnetic resonance imaging (MRI). However, in MS, data on the relation of OCT measures and grey and white matter volumes are contradictory. We performed a prospective cross-sectional study with a statistically pre-defined endpoint to test our hypothesis that OCT measures of neuro-axonal degeneration are related to global and partial brain atrophy in early forms of MS.

METHODS AND RESULTS: Forty-four patients with clinically isolated syndrome (n = 10) or relapsing-remitting MS (n = 34; mean disease duration = 3.2 years, median EDSS = 1.5) were enrolled in the study. Peripapillary- and volumetric OCT scans of the macula were performed using latest spectral-domain OCT technology. BPF as well as white and grey matter fractions (WMF/GMF) were assessed by 1.5 Tesla MRI scans. Generalized estimating equation models adjusted for age and linear regression statistics were used to assess the association between OCT and MRI measures. RNFL thickness, TMV and age were significantly associated with BPF. RNFL thickness and TMV independently predicted WMF (P = 0.003 and P = 0.032) but not GMF (P = 0.717 and P = 0.357) when corrected for age. In contrast, age was strongly associated with GMF (P < 0.001) but not WMF.

CONCLUSION: Our study suggests that, in early MS, OCT measures of retinal atrophy are related to volumetric changes in the white but not grey matter compartment as assessed by MRI. It further substantiates the association of retinal thinning and brain tissue loss in MS.

There has been a lot of interest about whether monitoring retinal thinning can provide a surrogate marker of brain disease. Retinal thinning can be see using scans taking a few seconds and machines are geared that serial monitoring would be cheap. The machines cost about £50-70,000 and compared to a few million for an MRI scan that takes much longer and takes a lot more computing power to detect change and alot more infrastructure to house and use. This study shows there is a better correlation with white matter changes rather than the grey matter. This is only a lose correlation and whilst useful I doubt it will replace brain imaging as the influence in the eye will be influenced what occurs in the optic nerve.

Dr Toosey presented details of this approach at the Research Day.

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