Purpose

Ideally, the multifocal electroretinogram (mfERG) is recorded without noticeable intrusion of mains interference. However, sometimes contamination is difficult to avoid. A post-processing digital notch filter can help to recover the retinal response even in severe cases of mains interference. While a digital filter can be designed to have little to no impact on peak times, filtering out mains interference also removes the retinal signal content of the same frequency, which may result in a change of amplitude. The present study addressed this issue in the standard first order kernel mfERG.

Methods

In 24 recordings from routine exams with no perceivable mains interference, the effects of 50-Hz and 60-Hz non-causal digital notch filters on amplitude and peak time were assessed. Furthermore, the effect of filtering on contaminated traces was demonstrated and simulated mains interference was used to provide an example of nonlinear superposition of retinal signal and mains interference.

Results

mfERG amplitudes were reduced by 0%–15% (median 6%) with the 50-Hz filter and remained virtually unaffected with the 60-Hz filter. Simulations illustrate that spurious high-frequency components can occur in the filtered signal if a strongly contaminated signal is clipped due to a limited input range of the analog-to-digital converter.

Conclusion

The application of a 50-Hz digital notch filter to mfERG traces causes a mild amplitude reduction which will not normally affect the clinical interpretation of the data. The situation is even more favorable with a 60-Hz digital notch filter. Caution is necessary if the assumption of linear additivity of retinal signal and mains interference is violated.

中文翻译：

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通过应用后处理数字陷波滤波器消除 mfERG 的电源干扰：好还是坏？

目的

理想情况下，记录多焦视网膜电图 (mfERG) 时不会有明显的电源干扰侵入。然而，有时污染是难以避免的。即使在电源干扰严重的情况下，后处理数字陷波滤波器也可以帮助恢复视网膜响应。虽然数字滤波器可以设计为对峰值时间几乎没有影响，但滤除主电源干扰也会去除相同频率的视网膜信号内容，这可能会导致幅度变化。本研究在标准一阶内核 mfERG 中解决了这个问题。

方法

在 24 个没有可感知电源干扰的常规检查记录中，评估了 50-Hz 和 60-Hz 非因果数字陷波滤波器对幅度和峰值时间的影响。此外，还展示了过滤对受污染痕迹的影响，并使用模拟电源干扰提供了视网膜信号和电源干扰非线性叠加的示例。

结果

使用 50-Hz 滤波器时，mfERG 幅度降低了 0%–15%（中值为 6%），而使用 60-Hz 滤波器时几乎不受影响。仿真表明，如果由于模数转换器的输入范围有限而对严重污染的信号进行削波，则滤波后的信号中可能会出现寄生高频分量。

结论

将 50 Hz 数字陷波滤波器应用于 mfERG 迹线会导致幅度轻微降低，这通常不会影响数据的临床解释。使用 60Hz 数字陷波滤波器时，情况更加有利。如果违反了视网膜信号和电源干扰的线性可加性假设，则必须小心。