To the Editor.
—A comparison of electrodes for electroretinography, as described by Gjötterberg,1 can be useful. However, it would have been preferable if the author had used a ganzfeld luminance source as a stimulator instead of a light source with a diameter of 12° or 15° (a photostimulator [Grass PS 22] at 75 cm distance). The retinal area that corresponds with this small field is 10 to 15 mm2, while the light-sensitive retina has a total area of about 1000 mm2. With such a focal stimulator, the electroretinogram mainly measures the response of an indirectly illuminated retina. This response is smaller than the response to a ganzfeld stimulus. Moreover, the differences between responses obtained in eyes with clear media and eyes with opaque media (cataracts, corneal edema) are larger as a result of differences in retinal light distribution.It cannot be assumed that electroretinographic responses with the use
Kooijman AC. Comparison of Electrodes for Electroretinography. Arch Ophthalmol. 1987;105(1):23. doi:10.1001/archopht.1987.01060010025010