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G.M. Tondel, J. Wang, T.R. Candy; Dynamic Aspects of Infants' Responses to Ramp Accommodative Stimuli . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1995.
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Purpose: Infants older than 3 months of age are able to detect and smoothly track a ramp accommodative target over a 3 D demand. The purpose for this study was to investigate the dynamics of infants' ramp responses. Methods: An eccentric videorefractor (PowerRefractor- Multichannel System) was used to sample accommodative responses of 7 to 19 week-olds and pre-presbiopic adults (as a comparison group). Measurements were taken at a frequency of 25Hz while targets were smoothly ramped back and forth between viewing distances of 1m and 25cm. Results: Infants, over the full age-range, were able to detect and change their accommodation in response to the 3 D demand. The latency and duration of the responses varied from infant to infant and also across age. Most infant responses were of shorter duration for negative than positive accommodation. This pattern was not found in the adults. The amplitude of accommodation was either matched or larger than the stimulus demand, and some infants initially accommodated in the incorrect direction. Conclusions: Young infants have the motor and sensory capacities to make positive and negative accommodative responses to ramp stimuli moving at 1D/sec. The variability in responses latency and duration could reflect the role of attention. The asymmetry in duration of positive and negative responses will be discussed in the context of depth of focus predictions.
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