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Takeshi Kumagami, Bin Zhang, Earl L. Smith, Yuzo M. Chino; Effect of Onset Age of Strabismus on the Binocular Responses of Neurons in the Monkey Visual Cortex. Invest. Ophthalmol. Vis. Sci. 2000;41(3):948-954.
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purpose. By 6 weeks of age, neurons in the monkey’s primary visual cortex
acquire qualitatively adult-like binocular response properties and
behaviorally stereopsis emerges. In this study, it was
determined whether the onset of strabismus has a more severe impact on
cortical binocularity before or after this critical developmental age.
methods. Infant monkeys were fit with a light-weight helmet which held a total
of 27 diopters of base-in prisms in front of their two eyes for a fixed
period of two weeks. For one group of infant monkeys, prism-rearing
began at 2 weeks of age and for a second group, the onset was at 6
weeks of age. Immediately after the rearing period, i.e., at 4 weeks
and 8 weeks of age, respectively, extracellular single-unit recording
methods were used to determine the nature and severity of alterations
in the binocular response properties of V1 neurons. Dichoptic
sinewave gratings were used as visual stimuli.
results. In comparison to normal age-matched infants, V1 neurons in both
strabismic groups exhibited reductions in sensitivity to interocular
spatial phase disparities (disparity sensitivity) and a higher
prevalence of binocular inhibitory interactions (binocular
suppression). However, the reduction in disparity sensitivity and the
magnitude of binocular suppression were much greater in the late (6–8
weeks) than the early (2–4 weeks) onset group.
conclusions. Discordant binocular signals due to brief periods of early strabismus
have more serious effects on the development of binocular properties of
V1 neurons if they occur shortly after rather than before the emergence
of stereopsis (i.e., when the binocular connections are relatively more
mature but the visual cortex still shows a high degree of
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