Rodríguez-Vallejo Manuel, Monsoriu Juan A, Furlan Walter D
*MS †PhD Qvision, Unidad de Oftalmología, Vithas Hospital Virgen del Mar, Almería, Spain (MR-V); Centro de Tecnologías Físicas, Universitat Politècnica de València, Valencia, Spain (JAM); and Departamento de Óptica, Universitat de València, Burjassot, Spain (WDF).
Optom Vis Sci. 2016 Dec;93(12):1532-1536. doi: 10.1097/OPX.0000000000000972.
To evaluate the reliability of measuring CS with uncalibrated iPads.
Six random iPads with retina display were calibrated with a colorimeter and the correlation between Luminance (L) and pixel level (y) was computed according to an exponential function. The mean and confidence interval (±2SD) obtained from the six iPads were calculated and the bit-stealing technique was applied for expanding y from 256 to 2540 possible values. The L of the optotype was computed for the selected contrast values (logC) represented in log units, using 0.1 log and 0.05 log steps. At each particular y, the contrast was considered reliable when the mean L plus 2SD was less than half the difference of luminance between two consecutive levels of contrast. Differences between the iPads for the Experimental logC were evaluated with the Friedman test.
Luminance properties vary between devices, which were reflected in the computed Experimental logC (p < 0.0005). The contrast was found to be reliable for 0.1 log steps in the range from 0 to -2.2 log. On the other hand, for steps of 0.05 log, the contrast was only reliable for values ranging from 0 to -1.7 log.
Both luminance and contrast steps differed between iPads with the same retina display, making it necessary to calibrate each display to achieve accurate luminance and contrast steps of 0.05 log units or less. However, for screening purposes utilizing contrast steps of 0.1 log unit or greater for a validated psychophysical test, calibration is not required to achieve accurate results across the displays described herein.
评估使用未经校准的iPad测量对比度敏感度（CS）的可靠性。
用色度计对六台随机选取的配备视网膜显示屏的iPad进行校准，并根据指数函数计算亮度（L）与像素水平（y）之间的相关性。计算从这六台iPad获得的平均值和置信区间（±2SD），并应用位窃取技术将y从256扩展到2540个可能值。对于以对数单位表示的选定对比度值（logC），使用0.1 log和0.05 log步长计算视标（optotype）的L。在每个特定的y值处，当平均L加上2SD小于两个连续对比度水平之间亮度差异的一半时，对比度被认为是可靠的。使用Friedman检验评估实验logC在各iPad之间的差异。
不同设备之间的亮度特性有所不同，这在计算出的实验logC中得到了体现（p < 0.0005）。发现在0至 -2.2 log范围内，0.1 log步长的对比度是可靠的。另一方面，对于0.05 log步长，对比度仅在0至 -1.7 log范围内是可靠的。
具有相同视网膜显示屏的iPad之间，亮度和对比度步长均存在差异，因此有必要对每个显示屏进行校准，以实现0.05 log单位或更小的准确亮度和对比度步长。然而，对于使用0.1 log单位或更大对比度步长进行经过验证的心理物理学测试的筛查目的，无需校准即可在此处所述的各显示屏上获得准确结果。
