Washington National Primate Research Center, University of Washington, Seattle, Washington, United States.
Department of Ophthalmology, University of Washington, Seattle, Washington, United States.
Invest Ophthalmol Vis Sci. 2019 Apr 1;60(5):1670-1676. doi: 10.1167/iovs.18-26440.
Convergence insufficiency is a very common disorder that can have significant adverse effects on school performance. When reading, children with this disorder often experience diplopia and headaches. We have recently obtained a rhesus monkey with a naturally occurring impairment of vergence eye movements. In the companion paper, we report behavioral testing that shows a pattern of impairments similar to what clinicians observe in human children with convergence insufficiency, including a receded near point, an exophoria that increases as target distance decreases, and difficulty maintaining an appropriate vergence angle when presented with a large field stimulus at near. For the present case report, we wondered whether these behavioral deficits would be associated with abnormal discharge patterns in brainstem neurons related to vergence eye movements.
Single unit activity was recorded from near and far response cells in the supraoculomotor area in the vergence-impaired monkey, while he performed a smooth vergence tracking task or fixated visual targets at different distances.
We found an abnormally weak sensitivity to both vergence angle and vergence velocity. Nonetheless, these neurons modulated in association with contextually inappropriate slow vergence movements that occurred in the absence of saccades but not for slow divergence drifts that immediately followed converging saccades. Modulation of activity was more robust when additional depth cues were available.
These data suggest that disorders affecting vergence eye movements may be associated with impoverished sensory input to the near and far response cells and, perhaps, aberrant tuning in vergence-related neurons.
集合不足是一种非常常见的障碍，它会对学校表现产生重大的负面影响。当阅读时，患有这种障碍的孩子经常会出现复视和头痛。我们最近得到了一只恒河猴，它有一种自然发生的会聚眼动障碍。在相关论文中，我们报告了行为测试的结果，表明存在一种类似于临床医生在患有集合不足的人类儿童中观察到的模式的障碍，包括近点退缩、随着目标距离减小而增加的外斜视以及在近点处呈现大视野刺激时难以维持适当的会聚角度。对于本病例报告，我们想知道这些行为缺陷是否与与会聚眼动相关的脑干神经元的异常放电模式有关。
在会聚障碍的猴子进行平滑会聚跟踪任务或在不同距离固定视觉目标时，从上眼球运动区的近点和远点反应细胞中记录单个神经元的活动。
我们发现对会聚角度和会聚速度的敏感性异常弱。尽管如此，这些神经元在没有扫视的情况下与上下文不适当的缓慢会聚运动相关联地调节，但不会与紧随会聚扫视的缓慢发散漂移相关联地调节。当有额外的深度线索时，活动的调节更加稳健。
这些数据表明，影响会聚眼动的障碍可能与近点和远点反应细胞的感觉输入不足有关，并且在会聚相关神经元中可能存在异常调谐。
