Nagy Balázs Vince, Gémesi Szabolcs, Heller Dávid, Magyar András, Farkas Agnes, Abrahám György, Varsányi Balázs
Department of Mechatronics, Optics and Engineering Informatics, Budapest University of Technology and Economics, Hungary.
Doc Ophthalmol. 2011 Jun;122(3):157-62. doi: 10.1007/s10633-011-9270-5. Epub 2011 Apr 8.
There are several electrophysiological systems available commercially. Usually, control groups are required to compare their results, due to the differences between display types. Our aim was to examine the differences between CRT and LCD/TFT stimulators used in pattern VEP responses performed according to the ISCEV standards. We also aimed to check different contrast values toward thresholds. In order to obtain more precise results, we intended to measure the intensity and temporal response characteristics of the monitors with photometric methods. To record VEP signals, a Roland RetiPort electrophysiological system was used. The pattern VEP tests were carried out according to ISCEV protocols on a CRT and a TFT monitor consecutively. Achromatic checkerboard pattern was used at three different contrast levels (maximal, 75, 25%) using 1° and 15' check sizes. Both CRT and TFT displays were luminance and contrast matched, according to the gamma functions based on measurements at several DAC values. Monitor-specific luminance parameters were measured by means of spectroradiometric instruments. Temporal differences between the displays' electronic and radiometric signals were measured with a device specifically built for the purpose. We tested six healthy control subjects with visual acuity of at least 20/20. The tests were performed on each subject three times on different days. We found significant temporal differences between the CRT and the LCD monitors at all contrast levels and spatial frequencies. In average, the latency times were 9.0 ms (±3.3 ms) longer with the TFT stimulator. This value is in accordance with the average of the measured TFT input-output temporal difference values (10.1 ± 2.2 ms). According to our findings, measuring the temporal parameters of the TFT monitor with an adequately calibrated measurement setup and correcting the VEP data with the resulting values, the VEP signals obtained with different display types can be transformed to be comparable.
市面上有几种商用的电生理系统。由于显示类型之间存在差异，通常需要对照组来比较结果。我们的目的是研究根据国际临床视觉电生理学会（ISCEV）标准进行的图形视觉诱发电位（VEP）反应中，阴极射线管（CRT）和液晶显示器/薄膜晶体管（LCD/TFT）刺激器之间的差异。我们还旨在检查不同对比度值与阈值的关系。为了获得更精确的结果，我们打算用光度学方法测量显示器的亮度和时间响应特性。为了记录VEP信号，使用了罗兰RetiPort电生理系统。图形VEP测试按照ISCEV协议在CRT和TFT显示器上依次进行。使用1°和15'的方格尺寸，在三种不同对比度水平（最大、75%、25%）下采用消色差棋盘格图案。根据基于几个数模转换器（DAC）值测量的伽马函数，CRT和TFT显示器的亮度和对比度都进行了匹配。通过光谱辐射测量仪器测量显示器特定的亮度参数。用专门为此目的制造的设备测量显示器电子信号和辐射信号之间的时间差异。我们测试了六名视力至少为20/20的健康对照受试者。测试在不同日期对每个受试者进行了三次。我们发现在所有对比度水平和空间频率下，CRT和液晶显示器之间存在显著的时间差异。平均而言，使用TFT刺激器时潜伏期长9.0毫秒（±3.3毫秒）。这个值与测量的TFT输入-输出时间差异值的平均值（10.1±2.2毫秒）一致。根据我们的研究结果，使用经过充分校准的测量装置测量TFT显示器的时间参数，并用所得值校正VEP数据，可以使不同显示类型获得的VEP信号具有可比性。
