THE GOLD FOIL ELECTRODE IN PATTERN ELECTRORETINOGRAPHY

A recent study found that the gold foil electrode produces large patte rn electroretinogram amplitudes, but the test-retest reliability was l ow. In a three-center study, we observed that 90% of 29 patients who w ere tested with gold foil electrodes used three times appeared to have markedly lower amplitudes than when tested with new electrodes during the same session. Across study centers, the mean of the new electrode recordings was 3.78 mu V (standard deviation, 1.13 mu V), versus 2.93 mu V (1.29 mu V) for used electrodes. This 0.85-mu V reduction (22%) was statistically significant (F = 7.10 p = 0.01). Electrodes used thr ee times demonstrated an average change in the coefficient of variatio n of 14% (standard deviation/mean = coefficient of variation; new, 1.1 3/3.78 = 30%; used, 1.29/2.93 = 44%). Two of the study sites (Houston/ Indianapolis) conducted test-retest pattern electroretinograms on a to tal of 18 patients and found the mean evoked potential to be 3.55 mu V with new electrodes and 2.82 mu V with used electrodes. The coefficie nt of variation for the test-retest data was 30% and 47% for new and u sed electrodes, respectively. Light microscopy showed small cracks on the surface of the electrode, with the number and configuration of the cracks varying in each electrode. The presence of cracks is further c omplicated by their proximity to the tear film. These sources of varia tion can result in significantly different impedances. We propose that constant flexion, as a result of patient blinking, causes cracks in t he thin gold surface of the electrode. Used electrodes will produce lo wer pattern electroretinogram amplitudes and poor test-retest reliabil ity. To minimize these problems, the gold foil electrode should only b e used a single time.