Tuesday, 7 April 2015

Optic neuritis - a collaboration of eyes and brain

Invest Ophthalmol Vis Sci. 2015 Mar 26. [Epub ahead of print]

An Eye on Brain Integrity: Acute Optic Neuritis Affects Resting State Functional Connectivity.

Abstract

PURPOSE:

Currently, the ability for imaging to capture brain adaptations to injury that occurs in multiple sclerosis (MS) is limited. In particular, how the brain initially contends with the earliest clinical manifestations of white matter injury has yet to be defined. The purpose of this study is to determine the impact of acute optic neuritis (ON) on resting state functional connectivity magnetic resonance imaging (rs-fcMRI).

METHODS:

Fifteen patients with a clinically isolated syndrome of acute ON were evaluated at an academic center in a prospective study. Subjects were assessed with structural and functional vision measures, including optical coherence tomography (OCT), high and low contrast letter acuity testing, visual fields and the quality of life measures (VFQ-25). rs-fcMRI was compared to age and gender matched healthy controls.

RESULTS:

We observed reduced functional connectivity within the visual system and a loss of anti-correlations between the visual system and non-visual networks. Stronger functional connectivity between visual regions correlated with better quality of life, as measured by the VFQ-25, and better acuity scores for both high and low contrast testing in the affected eye.

CONCLUSIONS:

rs-fcMRI functional connectivity changes within (intra-network) and between (inter-network) resting state networks occur after acute ON indicating immediate cortical responses to focal inflammatory demyelination. Thus, focal white matter injury in the central nervous system acutely results in widespread network alterations that may lead to functional neurologic changes seen in MS.

We already know that optic neuritis is the result of focal inflammation affecting the optic nerves. So how does as these researcher suggest, does focal white matter injury lead to a dysfunction in the perception of vision (i.e. a higher order cortical dysfunction)? 

It seems that disruption of the anterior visual pathways also leads to similar structural changes in the rest of the brain with wider network effects that reach beyond the visual center of the brain (see figure below). Moreover, there appears to be a reduction in brain connectivity even at the earliest stages of MS.