Direction-of-motion detection and motion VEP asymmetries in normal children and children with infantile esotropia

PURPOSE. To investigate nasal-temporal asymmetries in the detection of horizontal motion and in cortical motion visual evoked potential (mVEP) responses in normal infants and children and in patients with infantile esotropia. METHODS. Monocular motion-detection thresholds were obtained separately for nasalward- and temporalward-moving random-dot patterns in a forced-choice, preferential-looking paradigm. Monocular mVEP responses were obtained while subjects viewed a 6-Hz oscillating, 1 cyc/deg vertical sine-wave grating. Nasal-temporal mVEP asymmetry was investigated with two measures from each subject: asymmetric indices (AIs) and interocular phase differences. Performance was compared in 33 visits of 28 normal subjects and 73 visits of 54 patients with infantile esotropia, ranging in age from 2 months to 5 years. RESULTS. At 3 to 5 months of age, both normal infants and patients with infantile esotropia had robust nasal-temporal asymmetries in motion-detection and mVEP measures. By 2 years of age, measures in all normal subjects were symmetric, as they were in patients successfully treated with glasses or alignment surgery, whereas patients who had not yet undergone alignment surgery, regardless of surgery status, had highly asymmetric mVEP responses and motion-detection thresholds. CONCLUSIONS. Young normal and esotropic infants exhibited nasal-temporal asymmetries in both motion detection and mVEP. These asymmetries similarly disappeared over time in normal infants and in patients with esotropia who had received successful, timely correction of misalignment. Although the initial capacity for motion processing is normal in the youngest patients with untreated esotropia at 5 months, cumulative abnormal binocular experience in these patients may disrupt motion mechanisms.