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Richard Donkor, Caroline Teske, Margaret Wallis-Duffy, Michael Barnett-Cowan, Ben Thompson; Primary visual cortex transcranial random noise stimulation improves contrast sensitivity in adults with amblyopia. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6458.
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© ARVO (1962-2015); The Authors (2016-present)
Non-invasive anodal transcranial direct current stimulation (tDCS) of the primary visual cortex increases neural excitability and transiently improves contrast sensitivity in adults with amblyopia. Recently a new transcranial electrical stimulation paradigm called transcranial random noise stimulation (tRNS) has been developed. tRNS involves a randomly oscillating alternating current and increases cortical excitability while avoiding the polarity dependence of tDCS. We tested the hypothesis that a single session of visual cortex tRNS would improve contrast sensitivity in adults with amblyopia and that the effects would extend to crowded and uncrowded visual acuity.
Using a between-subjects design, 19 healthy adults with amblyopia (44.2 ± 14.9yrs, 10 female) underwent active or sham tRNS of the visual cortex (active n = 9, sham n = 10). tRNS was delivered for 25 minutes in a single session using a DC-STIMULATOR MC (Eldith, NeuroConn GmbH, Germany) through a pair of saline-soaked surface sponge electrodes (5 cm x 7 cm, 35 cm2) placed at electrode positions Cz (reference) and Oz (stimulating electrode). Monocular contrast sensitivity, uncrowded and crowded visual acuity were measured before, during, 5 minutes and 30 minutes post stimulation. All measurements were made using Landolt-C optotypes presented using the Freiburg Vision Test (‘FrACT’) software package.
A between subjects ANOVA revealed a significant interaction between Group (active vs. sham) and time (baseline, during, 5 mins post, 30 mins post) for amblyopic eye contrast sensitivity, whereby active tRNS significantly improved contrast sensitivity during, 5 and 30 mins post tRNS relative to baseline (t > 2.5, p < 0.04 for all comparisons) whereas sham tRNS had no effect at any time point (p > 0.05). There were no differences between active and sham tRNS groups for measures of amblyopic eye crowded or uncrowded visual acuity (p > 0.05).
Amblyopic eye contrast sensitivity improved for at least 30 minutes following a single session of tRNS, however this effect did not occur for measures of high contrast visual acuity. Future studies will reveal whether visual acuity changes occur after repeated sessions of visual cortex tRNS.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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