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J. Wang, T.R. Candy; The Threshold Stimulus for Accommodation in Human Infants . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5887.
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© ARVO (1962-2015); The Authors (2016-present)
Green, Powers & Banks (1980) performed a theoretical analysis to predict that human infants have a larger depth of focus than adults. This prediction was based on behavioral estimates of acuity. There are no empirical estimates of infants’ sensitivity to targets moving in depth. The goal of this study was to record infants’ accommodative responses to targets moving over a range of dioptric distances.
Full–term infants from 2–4 months of age and pre–presbyopic adults were presented with a high contrast cartoon stimulus moving sinusoidally in dioptres around a mean position of 2D (50cm). Three stimulus amplitudes were used: 0.25, 0.50 & 0.75D (corresponding to 0.5, 1 & 1.5D peak to trough). Three cycles, at 0.13 Hz, were presented at each amplitude with unpredictable stimulus movements between each of them. Eccentric photorefraction (Multichannel PowerRefractor) was used to record accommodative responses binocularly at 25Hz to the binocular stimulus presentation.
Analysis in the time domain demonstrated that the infants were able to track the stimuli well over time. An fft of the accommodative responses indicated that, on average, infants in this age range are able to generate an accommodative response to the 0.75 and 0.5D amplitude stimuli. Some responded significantly to the 0.25D stimulus.
Infants of 2–4 months of age are able to generate accommodative responses to binocular sinusoidal stimuli of at least 0.5D amplitude. This result suggests that the developing visual system is able to compensate for small amounts of defocus relative to the typical amounts of refractive error found at that age.
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