Distribution of pattern-evoked potentials in the facial area

Comparisons of contact lens, foil, fiber and skin electrodes for patterns electroretinograms

Pattern electroretinograms are small physiologic signals that require good patient cooperation and long recording times, particularly when conditions are not optimal. Six electrodes were compared to evaluate their efficacy. Pattern electroretinograms were recorded in eight healthy volunteers to high-contrast, pattern-reversal checks (40' width) with Burian-Allen, DTL fiber, C-glide, gold foil, HK loop and skin electrodes. Raw data for 320 reversals were analyzed off-line to evaluate signal amplitude, quality, P50 and N95 peak times, artifact rate and electrical noise. Insertion time, impedance and subjective comfort were also assessed. The Burian-Allen contact lens electrode gave the largest signal and lowest impedance but was the least comfortable and had the highest artifact rate (p < 0.01). A skin electrode on the lower eyelid produced the smallest pattern electroretinogram with the poorest quality (p < 0.05). The four other electrodes were foil or fiber electrodes in contact with the tear film, conjunctiva and/or the inferior cornea. The signal from these showed only minor differences. When electrodes are compared for pattern electroretinograms recording, the foil and fiber electrodes do not differ substantially but contact lens and skin electrodes show substantial disadvantages.

Electrodes and the recording of the human electroretinogram (ERG)

The development of electrodes for recording the human electroretinogram is reviewed. The salient features of the different types in use are described and evaluated. The relation performance of different types is used as a basis for examining the dipole model of the origin of electroretinographic signals and suggestions are made for imposing it.

Variability of the pattern electroretinogram

Conflicting results have been obtained concerning the parametric properties of the pattern electroretinogram. These discrepancies may be due to the large amount of variability inherent in recording amplitudes. We have found the variability within a single stimulus condition to be so large (ranging from 30% to 67% of the mean value) that it could mask any underlying spatial frequency tuning. Changing the stimulus conditions failed to significantly reduce the observed variability, although changing recording conditions produced some reduction. The use of a narrower rejection band, a greater number of sweeps, and placement of the reference electrode on the ipsilateral ear (as opposed to the ipsilateral temple) combined to decrease variability of the pattern electroretinogram within a single recording session; however, intersession variability remained high. Therefore one must be careful in evaluating data from this technique, and caution is advised in its clinical use.

Pre- and postoperative findings of pattern VECPs and ERGs in patients of orbital tumors

Two cases of orbital tumors were studied pre- and postoperatively by means of the pattern VECP and -ERG together with MRI-CT recordings. The visual functions in one patient deteriorated but those in the other recovered after operation. In both cases a relation was found between the VECPs and the subjective visual data.

Pattern electroretinogram and visual evoked cortical potential in ethambutol optic neuropathy

Forty-one eyes in 21 cases of ethambutol optic neuropathy were investigated for the pattern visual evoked cortical potential (VECP) and the pattern electroretinogram (ERG). In 21 of the eyes the disappearance VECP responses were not detectable. In the other 20 eyes the peak latency and amplitude of the disappearance VECP were delayed and decreased significantly compared with normal eyes. The recovery of the peak latency of the disappearance VECP in ethambutol optic neuropathy was faster than that of the amplitude. Twelve eyes in six patients were studied by pattern reversal ERG. Though the mean peak latency of the pattern ERG was within normal limits, the mean amplitude was decreased significantly. Our investigations indicated that ethambutol optic neuropathy disturbed not only the optic nerve but also the retina.

Facially distributed pattern-evoked potentials in multiple sclerosis

Among 56 established cases of multiple sclerosis in our clinic from April 1978 to March 1985, optic neuritis was found in 38; 21 cases were bilateral. We studied pattern-evoked potentials detected with 16 electrodes placed on both the scalp and the facial area. Pattern-evoked potentials (PERGs) were obtainable at the facial area in multiple sclerosis patients with optic neuritis, except in long-standing cases. However, a significant reduction of amplitude was found even in cases without optic neuritis. No correlation was found between visual acuity and amplitude or peak latency of PERGs in MS patients.

Check size and defocusing effects on equipotential maps of pattern-evoked electroretinograms

The spatial distribution of the pattern-evoked potentials on the face was studied with a simultaneous 16-channel recording system. The potentials had the first positive component at a peak latency of approximately 55 msec, which was much earlier than the latency of the response picked up from the scalp. The maximal potential value in the maps was found at the region around the stimulated eye. This configuration of the equipotential map was not influenced by defocusing and check size of the pattern, but was altered by changing the contrast. Our results of equipotential maps constructed at around 55 msec after pattern reversal proved that the responses recorded in the facial region originated in the retina and were not a reflection of the scalp potentials.

Clinical application of the pattern electroretinogram with lid skin electrode

Pattern evoked potentials were recorded simultaneously with an electrode placed on the skin of the lower eyelid, gold foil electrodes hooked on the right and left eyelids, and a skin electrode at Oz in normal subjects and in patients with optic nerve and macular diseases. Peak latencies and amplitudes of the pattern electroretinogram (PERG) were compared between the two electrodes. In both records, the peak latency showed no difference at 56.7 +/- 2.9 ms (mean +/- S.D.), while the amplitude of the PERG with the lid skin electrode was at 1.2 +/- 0.3 microV, approximately one-third of that obtained with the gold foil electrode. Although the skin electrode did not always record responses as well as the gold foil, its advantages recommend its use in clinical cases.

Pattern electroretinograms recorded with a skin electrode in pigmentary retinal degeneration

In 24 patients suffering from pigmentary retinal degeneration the electroretinograms to pattern stimulation (PERG) were recorded with a silver-cup electrode placed on the center of the lower eyelid skin referred to an electrode on the earlobe. The results were compared with the responses to flash stimulation (FERG) and pattern visual evoked cortical potentials. None of patients showed normal FERGs. Nineteen of 48 eyes showed subnormal FERGs. The PERG was recorded from those 19 eyes. In the remaining 29 eyes with flat FERG, 8 eyes showed clear PERGs. The peak latency of the first positive component of PERGs was found to be prolonged in these patients. PERGs seemed to be recordable in the patients whose visual acuity and central visual field were relatively well preserved.