Abstract
Amblyopia is a visual developmental condition that usually occurs when the brain receives abnormal input from one eye, but where and how neural problems arise is still unclear. Neuroimaging techniques like electroencephalography (EEG) are ideally suited for objectively measuring visual improvements following treatment for amblyopia, due to the good signal-to-noise ratio (SNR) in steady-state responses and avoiding issues of practice and response bias. Therefore, this study used a dry-electrode EEG system to objectively measure visual improvements in children (4-6 years old) following occlusion therapy (N=32). Neural responses to different contrasts presented monocularly, were measured before, during and after treatment using steady-state visual evoked potentials (SSVEPs). Stimuli were sinusoidal gratings with a spatial frequency of 3c/deg, flickering at 4 Hz. SSVEPs revealed better SNRs for the fellow eye compared to the amblyopic eye. Although the patterns of responses appear to show a reduction in the deficit from the amblyopic eye, the improvements in visual function between testing sessions fell outside of significance. However, significant improvements in the visual acuity of the amblyopic eye were measured after 6-8 weeks of treatment. This suggests that the treatment was effective in improving vision between the sessions but any neural changes between the eyes were not reflected in the SSVEPs measured using the dry-electrode EEG system. It is likely that the low sample size caused by high attrition rate (N=11 at the final session), combined with highly variable measurements, reduced the statistical power. Various improvements to the protocol to eliminate noise, such as ensuring the children fixate centrally, might enable more accurate data to be collected in the future. Overall, this study provides a first step in designing a paradigm where neural responses can be measured quickly and effectively, demonstrating the wider potential to apply dry-electrode EEG as an objective measure within mainstream clinical settings.