Reorganisation in the visual system of patients with macular degeneration
Final Report Abstract
Macular degenerations (MDs) have a great impact on the visual performance and the quality of life of the affected persons. Specifically, age-related MD is of major clinical interest as it is the leading cause of legal blindness in Western nations. In our investigations of the relationship of multifocal electrophysiology and visual function in MD and simulated visual impairment we obtained the following main results and conclusions: • MfERGs, mfPERGs, and mfVEPs are differentially effected by image degradations mimicking optic media opacities such as cataract. We conclude that combined recordings of mfERGs, mfPERGs, and mfVEPs give a very comprehensive account of the function of the retinal bipolar and ganglion cells and of the visual cortex, respectively. They thus allow for the assessment of the signal progression in the visual pathway and therefore for the identification of the effects of retinal damage on subsequent processing stages. Importantly, however, it must be noted that, as demonstrated by our results, the signal progression is highly non-linear and that incongruencies of the visual field topographies between retinal and cortical signals do not necessarily reflect compensatory processes of neural plasticity. • MfERGs recorded in patients with macular degeneration and eccentric fixation correlate with visual function, i.e. visual acuity and fixation instability. The high correlation of mfERG recordings in advanced MD with visual function highlights the significance of the mfERG-based objective assessment of retinal function even in MD with absolute central scotomas and its relevance for ophthalmological questions. • No specific changes of mfERGs at the preferred locus of fixation in MD with eccentric fixation were detected. We conclude that the location of the PRL, which is often located in the left lower visual field, might not be primarily due to retinal factors, but might also be influenced by a strong additional cortical determinant, potentially a generalized left hemifield dominance of visual processing. • Central mfERGs are the sole predictor of visual learning impairment in agerelated MD. The impairment of high-level visual function as assessed by incidental visual learning, specifically contextual cueing, is reflected by parafoveal mfERGs. This corroborates the prevalent notion that a parafoveal memory snapshot upon target fixation is relevant for contextual cueing effects. • Central mfVEPs are more strongly correlated with visual acuity than mfERGs. Likely due to differences in stimulation patterns/modes, mfVEPs are more sensitive to visual acuity differences than mfERGs. These findings indicate that visual function and multifocal electrophysiology are highly related and therefore demonstrate the high potential of electrophysiology to assess the consequences of retinal damage on visual function. Given that the impact of the state of the optical system is carefully taken into account, the recordings provide an objective account of the impact of macular degeneration on visual function. In fact, they allow for the assessment of the mechanisms of compensatory fixation strategies and of high-level visual function and their impairment.
Publications
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(2013) Contextual cueing impairment in patients with age-related macular degeneration. Journal of Vision 13(3) 28:1-18
Geringswald F, Herbik A, Hoffmann MB, Pollmann S
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(2013) Differential effects of optic media opacities on mfERGs and mfVEPs. Clinical Neurophysiology 124:1225-31
Herbik A, Hölzl GC, Reupsch J, Hoffmann MB
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(2014) Differential effects of optic media opacities on simultaneous multifocal pattern electroretinograms and multifocal visual evoked potentials. Clinical Neurophysiology 125:2418-2426
Herbik A, Thieme H, Reupsch J, Hoffmann MB
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(2014) Prediction of higher visual function in macular degeneration with mfERG and mfVEP. Ophthalmic and Physiological Optics 34:540-551
Herbik A, Geringswald F, Thieme H, Pollmann S, Hoffmann MB
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(2015) Visual memory for objects following foveal vision loss. Journal of Experimental Psychology Learning, Memory, and Cognition, 41(5), 1471-1484
Geringswald F, Herbik A, Hofmüller W, Hoffmann MB, Pollmann S
