Long Lasting Effects of Daily Theta Burst rTMS Sessions in the Human Amblyopic Cortex

BackgroundIt has been reported that a single session of 1 Hz or 10 Hz repetitive transcranial magnetic stimulation (rTMS) of the visual cortex can temporarily improve contrast sensitivity in adults with amblyopia. More recently, continuous theta burst stimulation (cTBS) of the visual cortex has been found to improve contrast sensitivity in observers with normal vision.Objective/HypothesisThe aims of this study were to assess whether cTBS of the visual cortex could improve contrast sensitivity in adults with amblyopia and whether repeated sessions of cTBS would lead to more pronounced and/or longer lasting effects.MethodscTBS was delivered to the visual cortex while patients viewed a high contrast stimulus with their non-amblyopic eye. This manipulation was designed to bias the effects of cTBS toward inputs from the amblyopic eye. Contrast sensitivity was measured before and after stimulation. The effects of one cTBS session were measured in five patients and the effects of five consecutive daily sessions were measured in four patients. Three patients were available for follow-up at varying intervals after the final session.ResultscTBS improved amblyopic eye contrast sensitivity to high spatial frequencies (P < 0.05) and there was a cumulative improvement across sessions with asymptotic improvement occurring after 2 daily sessions of stimulation. The contrast sensitivity improvements were stable over a period of up to 78 days.ConclusionsThese initial results in a small number of patients indicate the cTBS may allow for enduring visual function improvements in adults with amblyopia.