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PURPOSE: An orientation-specific visual evoked potential (osVEP) protocol was developed to probe meridional anisotropies in children with refractive amblyopia. The aim was to characterise the osVEP response in children with bilateral refractive amblyopia, evaluate the intra-session repeatability of the main osVEP components (C1, C2 and C3), coefficient of repeatability (CoR) of the response to gratings in different meridians and determine if refractive amblyopes have poorer repeatability as compared with non-amblyopic controls.\ud \ud METHODS: Children aged 4-7 years with newly diagnosed and untreated bilateral refractive amblyopia and non-amblyopic controls were recruited. Orientation-specific pattern-onset VEPs were recorded in response to an achromatic sinewave grating stimulus of 4 cycles per degree under monocular and binocular stimulation. The grating lines used for monocular stimulation were parallel with the subjects' most positive and negative astigmatic meridians when considered in sphero-minus cylinder form (Meridians 1 and 2, respectively). In subjects without astigmatism, meridians 1 and 2 were designated horizontal and vertical gratings, respectively. Binocular stimuli were presented with grating lines parallel to meridians 45, 90, 135 and 180°. The repeatability of latencies of the main osVEP components (C1, C2 and C3) were investigated using two successive osVEPs recordings for each stimulus meridian and the CoR for each component's latencies were assessed.\ud \ud RESULTS: Seven amblyopic children (Visual acuity (VA) ranging from 0.08 to 0.40 LogMAR in the less amblyopic eye and 0.26-0.52 LogMAR in the more amblyopic eye) and 7 non-amblyopic controls (VA ranging from 0.00 to 0.02 LogMAR in either eye), with a median age of 4.6 and 7.0 years, respectively, completed the study. C1 had the highest CoR for most conditions assessed. Ratio of CoRs C1:C2 was > 2 for all binocular meridians in controls and the 90 and 180 meridians in the amblyopes; C1:C3 was > 2 for the binocularly assessed 45, 90 and 135 meridians in the controls and the 90 and 180 meridians in the amblyopes; C2:C3 were all

Transient chromatic pattern visual evoked potentials (VEPs) have been found to be less repeatable in morphology in children than in adults at low to moderate chromatic contrasts. The purpose of this study is to investigate whether low repeatability of VEP components can be associated with high alpha power, in a comparison of alpha activity in children and adults. Transient chromatic contrast and achromatic resolution VEPs were recorded in children (n = 14, mean 9.6 years) and adults (n = 12, mean 21.8 years) with normal vision and assessed for repeatability. Isoluminant chromatic (magenta-cyan) and luminance-modulated achromatic grating stimuli were presented at and above psychophysical threshold levels, in pattern onset-offset at 2 Hz temporal frequency. EEGs (eyes closed and open) were recorded as single sweeps (1 s long) over three 30 s periods while facing a uniform computer display. An index of VEP detectability by observation was developed based on VEP component repeatability. The index was examined for correlations with alpha-wave parameters. Alpha power was calculated as the sum of the powers of 8-13 Hz frequencies of the EEG sweeps (using the discrete Fourier transform). Alpha power variability was calculated using the standard deviation of the powers of each sweep in a 30 s time period. The children had significantly higher alpha powers than the adults for both the eyes-open and eyes-closed conditions. Alpha power variability was significantly higher for the eyes-open condition only. There was no relationship between alpha power parameters and index of VEP detectability by observation for both the chromatic and achromatic grating stimuli. Poor repeatability of transient pattern VEPs is not associated with high alpha power or its variability in EEG measurements in older children or young adults at Oz.