Novel brain imaging approaches to understand acquired and congenital neuro-ophthalmological conditions

Abstract

Purpose of review: The arrival of large datasets and the on-going refinement of neuroimaging technology have led to a number of recent advances in our understanding of visual pathway disorders. This work can broadly be classified into two areas, both of which are important when considering the optimal management strategies. The first looks at the delineation of damage, teasing out subtle changes to (specific components of) the visual pathway, which may help evaluate the severity and extent of disease. The second uses neuroimaging to investigate neuroplasticity, via changes in connectivity, cortical thickness, and retinotopic maps within the visual cortex.

Recent findings: Here, we give consideration to both acquired and congenital patients with damage to the visual pathway, and how they differ. Congenital disorders of the peripheral visual system can provide insight into the large-scale reorganization of the visual cortex: these are investigated with reference to disorders of the optic chiasm and anophthalmia (absence of the eyes). In acquired conditions, we consider the recent work describing patterns of degeneration, both following single insult and in neurodegenerative conditions. We also discuss the developments in functional neuroimaging, with particular reference to work on hemianopia and the controversial suggestion of cortical reorganization following acquired retinal injury.

Summary: Techniques for comparing neuro-ophthalmological conditions with healthy visual systems provide sensitive metrics to uncover subtle differences in grey and white matter structure of the brain. It is now possible to compare the massive reorganization present in congenital conditions with the apparent lack of plasticity following acquired damage.

Figure 1. Neuroimaging can be applied to investigate neuro-ophthalmological disorders at multiple points in the visual pathway.

A indicates the normal visual pathway where input from the eyes is reorganised at the optic chiasm such that one cortical hemisphere represents one side of visual space. B is the extreme condition where damage to the eyes prevents any visual input reaching the brain. C and D illustrate disorders of the chiasm in which cortical organization is abnormal (C Achiasma; D Albinism). E shows the effects of cortical visual damage resulting in homonymous hemianopia, a loss of vision on one side of visual space.