LOW-NOISE ELECTRORETINOGRAM RECORDING TECHNIQUES IN RETINITIS-PIGMENTOSA

The achievement of a sharp retinal signal depends on many factors, par ticularly the stability of the electrodes on the corneal surface, the maximal reduction of electrical and electromagnetic disturbances and t he avoidance of the noise caused by events that are synchronous with t he stimulation. The availability of a low-noise recording system becom es critical in the detection of the electroretinogram in patients with retinitis pigmentosa. We studied an electroretinographic recording te chnique specifically designed to enhance the signal-to-noise ratio in patients with retinitis pigmentosa. The main features of the method ar e a membrane suction pump connected to the corneal electrodes to impro ve contact lens stability on the corneal surface, and a differential d erivation system to record the signal. One corneal electrode is used a s the recording electrode, while the other, acting as the reference el ectrode, is covered during full-field ganzfeld stimulation. In additio n, computerized averaging and signal postrecording analyses were perfo rmed on 100 iterations. The methods described here resulted in a sharp reduction in the number of undetectable electroretinograms in our cas e material (28.8%). This investigation demonstrates that some of the u ndetectable signals reported in the Literature may be due to noisy rec ording methods rather than to actually extinguished retinal responses.