Bach M
Elektrophysiologisches Labor, Universitäts-Augenklinik, Freiburg, Germany.
Optom Vis Sci. 1996 Jan;73(1):49-53. doi: 10.1097/00006324-199601000-00008.
The Freiburg Visual Acuity test is an automated procedure for self-administered measurement of visual acuity. Landolt-Cs are presented on a monitor in one of eight orientations. The subject presses one of eight buttons, which are spatially arranged on a response box according to the eight possible positions of the Landolt-Cs' gap. To estimate the acuity threshold, a best PEST (best Parameter Estimation by Sequential Testing) procedure is used in which a psychometric function having a constant slope on a logarithmic acuity scale is assumed. Measurement terminates after a fixed number of trials. With computer monitors, pixel-discreteness artifacts limit the presentation of small stimuli. By using anti-aliasing, i.e., smoothing of contours by multiple gray levels, the spatial resolution was improved by a factor of four. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m.
弗莱堡视力测试是一种用于自我测量视力的自动化程序。兰多尔特环（Landolt-C）以八种方向之一呈现在显示器上。受试者按下八个按钮中的一个，这些按钮根据兰多尔特环缺口的八个可能位置在反应盒上按空间排列。为了估计视力阈值，使用了最佳PEST（通过顺序测试进行最佳参数估计）程序，其中假设在对数视力尺度上具有恒定斜率的心理测量函数。在固定次数的试验后测量终止。对于计算机显示器，像素离散伪像限制了小刺激的呈现。通过使用抗锯齿，即通过多个灰度级对轮廓进行平滑处理，空间分辨率提高了四倍。因此，即使是带有倾斜缺口的小兰多尔特环的形状也足够了，并且可以在5米的距离测试从5/80（0.06）到5/1.4（3.6）的视力。
