Andre J T, Owens D A
Franklin & Marshall College, Lancaster, Pennsylvania 17604-3003, USA.
Hum Factors. 1999 Mar;41(1):139-45. doi: 10.1518/001872099779577309.
Leibowitz and his colleagues found that accommodation rests at an intermediate distance that shows wide interindividual variation. They proposed that this intermediate dark focus is useful for correcting anomalous refractive errors, but this proposal was later questioned when different measurement techniques yielded discrepant dark focus values. The present study measured dark focus under two levels of visual attentiveness: (a) when performing an open-loop, active viewing task (aDF); and (b) when looking passively into darkness (pDF). These dark focus measures were then compared with an optimal accommodation distance that was derived from accommodative response functions in bright and dim luminance. The aDF measures were found to be more myopic (nearer) than the pDF measures and highly correlated with the optical accommodation distance. No significant relationship was found between pDF and optical accommodation distance. These findings confirm that measures of dark focus are affected by nonoptical aspects of the measurement technique; they also suggest that techniques that demand visual attention (aDF) yield dark focus values that are more useful for optimizing accommodation and potentially reducing fatigue in difficult situations.
莱博维茨及其同事发现，调节在一个中间距离处静止，该距离存在较大的个体间差异。他们提出，这个中间暗焦点有助于矫正异常屈光不正，但后来当不同的测量技术得出不一致的暗焦点值时，这一观点受到了质疑。本研究在两种视觉注意力水平下测量暗焦点：（a）执行开环主动观看任务时（aDF）；（b）被动看向黑暗中时（pDF）。然后将这些暗焦点测量值与从明、暗亮度下的调节反应函数得出的最佳调节距离进行比较。发现aDF测量值比pDF测量值更近视（更近），且与光学调节距离高度相关。未发现pDF与光学调节距离之间存在显著关系。这些发现证实，暗焦点测量受测量技术非光学方面的影响；它们还表明，需要视觉注意力的技术（aDF）产生的暗焦点值对于优化调节以及在困难情况下潜在地减轻疲劳更有用。
