Gall R, Wick B, Bedell H
College of Optometry, University of Houston, Texas.
Optom Vis Sci. 1998 Oct;75(10):731-42. doi: 10.1097/00006324-199810000-00018.
Vergence facility testing attempts to assess the ability of the fusional vergence system to respond rapidly and accurately to changing vergence demands over time [defined as the number of cycles per minute (cpm) that a stimulus can be fused through, alternating base-in (BI) and base-out (BO) prisms]. Decisions to use vergence facility as a clinical test are hampered by a lack of systematically gathered normative data.
Twenty symptomatic and 20 control subjects with ages between 18 to 35 years of either sex and any race were pooled, based on vision-symptom level determined by a self-report questionnaire. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye and normal phorias. Vergence facility response was tested over a 1-min period, using 16 combinations of BI/BO flip prisms at 4.0 and 0.4 m, based on Morgan's norms and pilot data.
Horizontal vergence facility responses were not the same among those with and without symptoms, and not all magnitudes of BI/BO flip prisms produced the same response difference. A single flip prism, 3 delta BI/12 delta BO, was found to differentiate optimally between groups at distance and near. Repeatability of test results (with the 3 delta BI/12 delta BO prism) was poor at distance and good at near.
In addition to providing valuable normative data, this study indicates that the vergence system nearly resets its "zero point" at any distance and sheds further light on the results of dynamic convergence and divergence stimulation on the accommodative-vergence system. From a clinical standpoint, the results improve the diagnosis of binocular vision abnormalities. The recommended near vergence facility test is easily implemented, using a commonly available flip prism (3 delta BI/12 delta BO) and having a clinical failure criterion that is easily recalled (15 cpm, sum of the BI and BO magnitudes).
聚散功能测试旨在评估融合性聚散系统随时间对变化的聚散需求做出快速准确反应的能力[定义为通过交替进行内聚（BI）和外聚（BO）棱镜融合刺激的每分钟周期数（cpm）]。由于缺乏系统收集的正常数据，使得将聚散功能用作临床测试的决策受到阻碍。
根据自我报告问卷确定的视觉症状水平，汇集了20名有症状和20名对照受试者，年龄在18至35岁之间，性别和种族不限。纳入/排除标准包括每只眼睛视力可矫正至6/6（20/20）Snellen视力或更好且隐斜正常。根据摩根的标准和预试验数据，使用4.0米和0.4米处的16种BI/BO翻转棱镜组合，在1分钟内测试聚散功能反应。
有症状和无症状者的水平聚散功能反应不同，并非所有大小的BI/BO翻转棱镜都产生相同的反应差异。发现单个翻转棱镜，即3棱镜度BI/12棱镜度BO，在远近距离下能最佳地区分不同组。测试结果（使用3棱镜度BI/12棱镜度BO棱镜）在远距离时重复性差，在近距离时重复性好。
除了提供有价值的正常数据外，本研究表明聚散系统在任何距离几乎都会重置其“零点”，并进一步阐明了动态聚散刺激对调节性聚散系统的结果。从临床角度来看，这些结果改善了双眼视觉异常的诊断。推荐的近距离聚散功能测试易于实施，使用常用的翻转棱镜（3棱镜度BI/12棱镜度BO），且具有易于记忆的临床失败标准（15 cpm，BI和BO量值之和）。
