Abstract
Purpose :
This study explores the impact of transcranial direct-current stimulation (tDCS) on fixation stability in visually normal adults, focusing on the cerebellum's role in maintaining saccades, vergence, and steady fixation, crucial for comfortable binocular vision.
Methods :
Five healthy adults with normal vision with no history of neurological or psychiatric conditions underwent sham and anodal tDCS (a-tDCS) in a randomized, single-blind crossover design. Stimulation parameters included a 20-sec fade in, 20-sec fade out, and 25 mins of 0 Amp current for sham, and 2000µAmp current for a-tDCS over 25cm2. Stimulation targeted the posterior cerebellum, utilizing Eyelink 1000plus tower at 1000Hz for eye movement recordings. Fixation data were collected monocularly and binocularly, along with saccadic adaptation and stereopsis tests. One-degree disc shaped visual target presented for 30 seconds monocularly and binocularly for fixation task. The adaptation test included 50 trials visually guided saccades, 150 trials of inward double-step saccadic adaptation paradigm, and 50 trials of visually guided saccades. Stereopsis was tested with a random dot stereogram.
Results :
No significant difference in saccadic gain pre and post-neuromodulation was found in the anodal tDCS (Kruskal-Wallis, H=4.1, df = 2, p=0.128) as well as sham groups. Peak velocity increased significantly after 10 minutes of anodal stimulation (Mann-Whitney, U=50645.00, p=0.034), but no differences were observed after 30 minutes (p=0.96). The double-step saccadic adaptation program showed a decrease in saccadic gain after adaptation in both sham and anodal tDCS groups (Mann-Whitney, T=63271, p<0.001). Fixation stability exhibited no significant difference after anodal or sham stimulation. Vergence stability during sham neuromodulation showed no significant difference (F=1.73, df = 2, p=0.19), but a significant improvement was noted after anodal neuromodulation (Kruskal-Wallis, H=11.94, df = 2, p=0.003). No significant difference in fine stereopsis was found before and after stimulation in both groups.
Conclusions :
The transient peak velocity increase post-a-tDCS, without altering saccadic gain, implies an intricacy in temporal and spatial aspects of oculomotor control. Improved vergence stability underscores tDCS's modulatory influence on binocular coordination, warranting further exploration for clinical applications.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.