—I appreciate Dr Kooijman's detailed comments. I fully agree with him that you get different responses with a ganzfeld stimulator than with a focal stimulator. However, the crucial point is that the same light stimulus is used with each electrode. Of course, as Dr Kooijman suggests, it would be interesting to perform another study with the use of a ganzfeld stimulator and compare the results. As Dr Kooijman has shown, other problems may arise when a ganzfeld stimulator is used because of the vignetting caused by some electrodes.The other point made in the comment is that of the coating agent. I must admit that it cannot be ruled out that even 0.5% hydroxypropyl methylcellulose might lower the amplitude in comparison with saline as a coating agent. As the aim of my study was to compare the registrations of different electrodes used in clinical practice, I just used
Gjötterberg M. Comparison of Electrodes for Electroretinography-Reply. Arch Ophthalmol. 1987;105(1):23. doi:10.1001/archopht.1987.01060010025011
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