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B. Thompson, B. Mansouri, L. Koski, R. F. Hess; rTMS: A New Treatment Possibility for Amblyopia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2834.
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The purpose of this study was to test the potential of repetitive transcranial magnetic stimulation as a treatment for visual loss in amblyopia. rTMS is a non-invasive technique for modulating excitability and inhibition in the cortex. Given the cortical basis of the visual loss in amblyopia and the link between intracortical inhibition and recovery of vision in amblyopia animals, we hypothesized that rTMS may have a therapeutic effect in amblyopic humans.
Seven adult strabismic amblyopes participated in the study. Contrast sensitivity for the amblyopic and fellow fixing eyes was tested for one high and one low spatial frequency before and after delivery of 600 pulses of 1Hz rTMS over visual cortex. The fellow fixing eye acted as a control measurement as no change in visual function was anticipated for this eye. A further control was the delivery of rTMS over motor cortex to test for non-specific effects of rTMS administration. Two participants who did not respond to the 1hz rTMS were tested with 900 pulses of 10hz rTMS (5 second trains, 45 second inter-train-interval) over visual cortex.
Five out of seven participants showed a high spatial frequency specific improvement in their amblyopic eye contrast sensitivity directly after 1hz rTMS over visual cortex and a further improvement 30 mins after rTMS administration. The remaining two participants who did not respond to 1hz rTMS did respond to 10hz rTMS administration over visual cortex with a high spatial frequency specific improvement in contrast sensitivity. No reliable changes in contrast sensitivity were found for the fellow fixing eyes and rTMS over the motor cortex had no effect on contrast sensitivity for either eye.
Our initial results suggest that rTMS may be a promising treatment intervention in amblyopia. We hypothesize that the therapeutic effect is modulated by changes in cortical inhibition, however other explanations including changes in neural excitability and neural synchrony cannot currently be ruled out. The reported effects of a single dose of rTMS are transient, however repeated doses may lead to more sustained improvement. Another potentially effective application would be to combine rTMS with behavioral training régimes to optimize the therapeutic effects of perceptual training paradigms.
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