Reorganisation in the visual system of patients with macular degeneration

• Applicant: Professor Dr. Michael Hoffmann, from 2/2009 until 1/2012
• Subject Area: Ophthalmology
• Term: from 2009 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 141192029

Macular degeneration (MD) deprives the cortical representation of the fovea from input, leaving an extensive part of the visual cortex unused. It is unresolved and currently very controversially discussed, whether mechanisms of cortical reorganisation make this cortical resource available for visual processing. Thus MD is, beyond its clinical relevance, a powerful model to study plasticity in the human visual cortex. In the current project the impact of foveal dysfunction and the establishment of an eccentric preferred locus of fixation (PRL) on the retinotopic organisation of the visual cortex, on top-down modulation, and on temporal aspects of visual processing shall be investigated with a multimodal approach of psychophysics, electrophysiology, and fMRI. Specifically, we are planning (i) a comparison of retinal and cortical visual field maps obtained with non-invasive electrophysiology in 40 patients with different types of MD to uncover to date unknown damage mechanisms and changes to the timing of cortical processing at the PRL; (ii) fMRI-based retinotopic mapping of the visual cortex in 24 MD patients, to specify course and mechanisms of the cortical reorganisation induced by foveal dysfunction and the establishment of a PRL; (iii) fMRI and VEP assessment of attention-related modulations in the visual cortex of 16 MD patients, to detail the reorganisation of top-down modulation. The fMRI investigations will be conducted at a magnetic field strength of 7 Tesla, as this allows for a high-resolution analysis of the cortical visual field representation. All patient data will be compared to matched controls. This multimodal imaging approach will detail mechanisms underlying pathophysiology and plasticity of the human visual system and allow us to assess, whether visually induced activity patterns are predictive for the position of the PRL. We expect to further the understanding of reorganisation in the human visual cortex and to contribute to resolving the ongoing controversy on plasticity in MD. Further, the results are likely to be of value for future therapeutic interventions and might open novel routes for visual rehabilitation in MD patients.

• DFG Programme: Research Grants