Infants’ Accommodative and Vergence Responses to Ramp Stimuli Under Binocular and Monocular Viewing Conditions

Abstract

Abstract: : Purpose: Clear, single vision depends on a dynamic balance between accommodation and vergence. Imbalance between theses two mechanisms is known to create binocular anomalies (e.g. esotropia). The goal of this study was to investigate dynamic accommodative and vergence responses of infants in both closed and open loop vergence conditions. Methods: An eccentric videorefractor (PowerRefractor – Multichannel Systems) recorded binocular refraction and gaze position of infants younger than 5 months and young adults. Vergence open loop conditions were created using a longpass filter, which permitted monocular viewing conditions during binocular data collection. Data were collected at 25Hz while targets were smoothly ramped at a velocity of 0.05m/s between 0.5m and 0.2 m. Results: Infants were able to generate accommodative and vergence responses to the ramped binocular stimulus. The vergence open loop data suggest that most infants were able to generate accommodative responses to the monocular stimulus. Vergence responses were not always detected to the monocular stimulus in younger infants but became more frequent with age. The infants exhibited longer accommodative and vergence latencies than adults both binocularly and monocularly, although the relationship between accommodation and vergence latency was similar in the two groups. In addition monocular responses had longer latencies than binocular in both age groups. Conclusions: The results confirm that infants are able to generate both accommodative and vergence responses under binocular and monocular viewing conditions. The shorter latencies recorded here under closed loop conditions indicate that binocular cues are helpful for both accommodation and vergence mechanisms in infancy. The presence of vergence responses under open loop conditions shows that the vergence mechanism is able to be triggered by monocular cues (proximity or the AC/A link). Acknowledgements: Help with data collection from Diane Goss, Heather McGill and Jingyun Wang and equipment development by William Monette.

Keywords: infant vision • visual development