Electrophysiology and psychophysics of children with newly-diagnosed refractive (non-strabismic) amblyopia and the effect of optical treatment

Optical treatment is the primary treatment of all types of amblyopia that has a refractive component. However, it is unclear how optical treatment impacts cortical processing in amblyopic children as some of them may readily improve letter recognition visual acuity (treatment responders) but others may not (treatment non-responders). The main aim was to investigate the electrophysiological and psychophysical effects of optical treatment in children who have been newly-diagnosed with amblyopia in comparison with normal maturation in non-amblyopic children. The secondary aim was to explore whether pattern onset-offset visual evoked potentials (POVEPs) and psychophysical grating acuities (GA) may be predictive of clinically significant improvements in letter recognition visual acuity (VA) after four months of optical treatment. The primary outcome measures were POVEP C3 amplitude and C3 latency and GA which were assessed in response to orientation-specific stimuli. The testing protocol was designed to optimize the assessment of meridional anisotropies and was able to identify children with refractive amblyopia and to monitor treatment outcomes. The study presented evidence that four months of optical treatment improved POVEP C3 amplitude on average, although within the amblyopic group, a subset of refractive amblyopes were not found to significantly improve in letter visual acuity. A comparison control group, comprised of non-amblyopic children, were also monitored over two visits four months apart, which represented age-normal characteristics and maturation. Meridional anisotropies were found to be a potentially useful indicator of normality, as there was evidence that orientation-specific neural mechanisms differed for the responders and non-responders to optical treatment, with the responders showing anisotropies more consistent with the control data. An onset of horizontal effect may indicate that the amblyopic visual systems are improving. Consequently, lower POVEP C3 amplitude in response to horizontally oriented grating stimuli at baseline was found to be a potential predictor of responder status after four months of optical treatment. The findings added new knowledge into the understanding of the electrophysiological and psychophysical effects of optical treatment in refractive amblyopia.