|Title||THE EFFECT OF ONSET AGE OF OPTICAL STRABISMUS ON THE BINOCULAR RESPONSE PROPERTIES OF NEURONS IN THE MONKEY VISUAL CORTEX|
|Author, Co-Author||Bin Zhang, Kazuki Matssuura, Earl SmithÊIII, Yuzo Chino|
|Abstract|| PURPOSE. One of the most commonly debated issues concerning the management of infantile strabismus is at what age does proper alignment need to be restored to preserve stereoscopic vision. To gain insight into this critical issue in vision development, we have been investigating the normal and abnormal development of the monkey visual cortex. By 6 weeks of age, neurons in the primary visual cortex acquire qualitatively adult-like response properties and behaviorally stereopsis emerges. In this study, we 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, 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, single-unit recording methods were employed to determine the nature and severity of alterations in the binocular response properties of V1 neurons.
RESULTS. In comparisons to normal age-matched infants, V1 neurons in both strabismic groups exhibited reductions in sensitivity to interocular image disparities and the higher prevalence of binocular suppression. However, the reduction in disparity sensitivity and the magnitude of binocular suppression were much greater in the late versus the early onset group.
CONCLUSION. Discordant binocular signals have more serious effects on the development 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 plasticity.
|Affiliation of Co-Authors||University of Houston, Department of Ophthalmology Tottori University Faculty of Medicine Yonago, University of Houston|