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J. Wang, S. R. Bharadwaj, T. R. Candy; The Monocular Threshold Stimulus for Accommodation in Human Infants. Invest. Ophthalmol. Vis. Sci. 2007;48(13):964.
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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. Wang & Candy (2006 ARVO) reported that infants of 2-4 months of age are able to generate accommodative responses to binocular sinusoidal stimuli of 0.5D amplitude. The goal of this study was to determine infants’ monocular stimulus threshold for an accommodative response.
Full-term infants from 2-4 months of age and pre-presbyopic adults were presented with a high contrast cartoon stimulus moving sinusoidally in diopters 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 of each amplitude were presented at 0.1 Hz, with unpredictable stimulus motion during each amplitude change. Eccentric photorefraction (Multichannel PowerRefractor) was used to record accommodative responses binocularly at 25Hz. The stimulus was made monocular by placing an IR filter over the right eye. This filter blocked visible light but passed the near IR wavelength of the PowerRefractor to allow responses to be recorded.
Fourier analysis was used to determine the response at the frequency of the stimulus. The response at 0.1Hz was compared with the amplitude at adjacent frequencies, as an estimate of the background noise. The signal to noise ratios indicated that, on average, the infants were able to generate an accommodative response to the 0.75D amplitude monocular stimulus and 0.50D binocular stimulus. Adults responded to the 0.25D amplitude both binocularly and monocularly.
Using Green, Powers and Banks’ analysis, the monocular results are consistent with a DOF prediction of ±0.6D based on three-month-old monocular FPL acuity data (Mayer, et al. 1995), while the binocular results are consistent with the binocular DOF prediction of ±0.44D, based on binocular FPL acuity data (Atkinson et al. 1977; Allen, 1979; Bank and Salapatek, 1978).
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