Vergence Adaptation to Short-Duration Stimuli in Early Childhood

PURPOSE To investigate whether nonstrabismic typically developing young children are capable of exhibiting vergence adaptation. METHODS Fifteen adults (19.5-35.8 years) and 34 children (2.5-7.3 years) provided usable data. None wore habitual refractive correction. Eye position and accommodation were recorded using Purkinje image eye tracking and eccentric photorefraction (MCS PowerRefractor). Vergence was measured in three conditions while the participant viewed naturalistic targets at 33 cm. Viewing was monocular for at least 60 seconds and then binocular for either 5 seconds (5-second condition), 60 seconds (60-second), or 60 seconds through a 10-pd base-out prism (prism 60-second). The right eye was then occluded again for 60 seconds and an exponential function was fit to these data to assess the impact of adaptation on alignment. RESULTS The 63% time constant was significantly longer for the prism 60-second condition (mean = 11.5 seconds) compared to both the 5-second (5.3 seconds; P = 0.015) and the 60-second conditions (7.1 seconds; P = 0.035), with no significant difference between children and adults (P > 0.4). Correlations between the 63% time constant (prism 60-second condition) and age, refractive error, interpupillary distance (IPD), or baseline heterophoria were not significant (P > 0.4). The final stable monocular alignment, measured after binocular viewing, was similar to the baseline initial alignment across all conditions and ages. CONCLUSIONS For a limited-duration near task, 2- to 7-year-old children showed comparable levels of vergence adaptation to adults. In a typically developing visual system, where IPD and refractive error are maturing, this adaptation could help maintain eye alignment.