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K. H. Gray, T. R. Candy, J. Wang, S. R. Bharadwaj; The Threshold Stimulus for Accommodation in 2 and 3 Year Olds Under Binocular Viewing Conditions. Invest. Ophthalmol. Vis. Sci. 2007;48(13):965.
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The most common age of onset of refractive esotropia is at 2 or 3 years of age (e.g. Parks 1958). The esotropia is typically attributed to excessive convergence driven by accommodative effort. While the binocular accommodative thresholds of 3-month-old infants and adults have been described earlier, little is known about the accommodative thresholds of young children. The goal of this study was to determine the baseline binocular accommodative thresholds of a group of 2 and 3 year olds with levels of hyperopia that are rarely associated with refractive esotropia (e.g. Parks 1958).
2 and 3 year olds with no optical correction, and pre-presbyopic adults (comparison population) were presented with high contrast cartoon images 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 at the transition from one amplitude to the next. Eccentric photorefraction (Multi Channel PowerRefractor) was used to record accommodative responses binocularly at 25Hz. Each child also underwent a full eye exam including cycloplegic refraction.
Cycloplegic refractive errors of the 2 and 3 year old subjects were consistent with those noted at these ages in the literature (Mayer et al., 2001). The range of spherical equivalents was from plano to +2.50. None of the subjects had evidence of strabismus. These subjects were able to robustly track the sinusoidal accommodative stimulus. Frequency domain analysis of their responses indicated that they were able to generate phase-locked responses at the temporal frequency of the stimulus at all of the amplitudes tested (the range of signal to noise ratios was from 5 to 9). The adults were also able to generate phase-locked responses to all stimulus amplitudes (SNR range from 5 to 17).
The threshold stimulus for accommodation under binocular viewing conditions for 2 and 3 year olds is close to that of adults (both generate responses to stimuli of 0.25D). Thus a group of subjects with low hyperopia and no strabismus are capable of performing at almost adult levels in naturalistic conditions.
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