Abstract
Purpose :
Amblyopia is a neurodevelopmental disorder causing deficits in spatial and temporal vision, resulting from abnormal early-life visual experiences. Because of reduced neuroplasticity in adults, traditional methods of amblyopia treatment often do not work. Our previous study showed that multiday sessions of transcranial random noise stimulation (tRNS), a type of non-invasive brain stimulation, in binocular adults boost cortical excitability. In this double-blinded study, we investigated whether such multiday stimulation on the visual cortex imparts cumulative and lasting effects on cortical excitability and clinical measures of vision in adults with amblyopia.
Methods :
23 adults (27±7 years) with amblyopia were enrolled. In a baseline session, phosphene thresholds (the minimum intensity of visual cortex transcranial magnetic stimulation required to induce a phosphene percept) were measured. 16 of 23 adults could reliably detect phosphenes and continued with the study. The participants were then randomly assigned to the treatment (tRNS) or control (sham stimulation) group and completed five consecutive daily tRNS/sham sessions. tRNS (1mA, 100-640Hz) or sham stimulation was applied to the primary visual cortex for 40 mins. Outcome variables included phosphene thresholds (PT), crowded visual acuity (CVA), contrast sensitivity (CS), and stereoacuity sensitivity (SS), which were measured pre- and post-tRNS/sham stimulation on each stimulation day, and then 24h, 72h, and 10-day post-treatment.
Results :
tRNS induced a cumulative, daily reduction in PT (pre-day1 vs. post-day5: 21 ± 9%) indicating improved cortical excitability. Such improvement was also observed in the clinical measures of vision between the pre-day 1 and post-day 5 (CVA: 0.3 logMAR ± 0.04, CS: 0.4 logCS ± 0.08, SS: 0.004 ± 0.006 arc s-1). These effects on PT and visual functions were still significant 24h (p values < 0.001) and 72h (p values 0.001 to 0.005) later. However, that effect waned when remeasured 10-day post-stimulation in 5 of 8 participants. There was no change in outcome variables following sham stimulation.
Conclusions :
Our results provide the first evidence of a sustained increase in cortical excitability and visual functions in adult amblyopia, using multi-day non-invasive brain stimulation, alone. Future research should explore the long-term efficacy of tRNS to treat adult amblyopia.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.