Gold foil electrodes: a two-center study of electrode reliability

The effect of topical anesthesia on the rat electroretinogram

Topical anesthetics are recommended when electroretinograms (ERGs) are recorded using contact lens electrodes. However, these drugs act by blocking voltage-gated Na+ channels. Since such channels have been located in both the inner and outer retina of many species, topical anesthesia could affect the ERG recordings in these subjects. The purpose of this study was to evaluate the effects of oxybuprocaine, a commonly used ester local anesthetic, on the rat ERG. Full-field scotopic and pattern ERGs (PERGs) were recorded successively from both eyes of seven rats. One eye was randomly treated with oxybuprocaine 15 min prior to recording. In 10 rats unilateral full-field photopic ERG recordings were conducted prior to, and 15 min after, treatment. B-wave amplitude ratios of the experimental/control eyes were 1.13, 1.30, and 1.35 for the three intensities used to record scotopic ERG responses, and 1.04 for the photopic ERG responses. PERG amplitude ratios of the experimental/control eyes were 1.10, 1.21, 1.21, 1.24, and 1.26 for the five patterns used. Treatment had no significant negative effect on signal amplitude or implicit time of the full-field ERG or PERG. In fact, amplitudes of signals from treated eyes tended to be (insignificantly) higher, though this might reflect better position of the active electrode rather than a biological effect. We conclude that oxybuprocaine has no negative effect on the rat ERG.

A comparison of two patient-friendly ERG electrodes

The ideal electroretinography (ERG) electrode does not exist. In deciding which electrode should be used in clinical practice the capacity to provide reproducible waveforms, maximal amplitudes and minimal irritation to the patient's eyes are the most important characteristics. This study tested two patient friendly electrodes, the gold foil (CH Electrodes, UK) and the H-K loop (Avanta, Slovenia). Seventeen normal volunteers were subjected to three standard measurements namely flash ERGs under photopic and scotopic conditions and the transient pattern ERG (PERG). Each test followed the guidelines set by the International Society for Clinical Electrophysiology of Vision (ISCEV). It was found that the mean values of the flash ERG a and b wave amplitudes and the PERG P50 and N95 amplitudes from the gold foil electrodes were approximately a factor of two larger than those from the H-K loop. In addition most of the subjects (13/17) felt less discomfort with the gold foil electrodes. We reached the conclusion that gold foil electrodes are the electrode of choice because they provide good patient comfort, reasonably high amplitudes and relatively reproducible results.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Electrophysiological findings in dominant optic atrophy (DOA) linking to the OPA1 locus on chromosome 3q 28-qter

Pattern and flash visual evoked cortical potentials (PVEP, FVEP), and pattern electroretinograms, (PERG) were recorded in 13 affected individuals from 8 families with DOA. These were selected as representative from 87 affected members of 21 pedigrees with DOA who were examined, and who underwent genetic linkage analysis. Linkage to the OPA1 locus on chromosome 3q 28-qter was demonstrated in all families. VA ranged from 6/9 to HM: visual fields showed a variable centro-caecal defect; SLO (when performed) showed diffuse nerve fibre loss; MRI (when performed) showed small intra-orbital optic nerves. In 9/13 patients the PVEP was absent in one or both eyes. Most recordable PVEPs were of abnormal latency, but the delays were not marked (peak times 116-135 msec); amplitudes were low or subnormal. PERG fell within the normal range in 9 eyes of 7 patients. 14 eyes showed an abnormal N95:P50 ratio in keeping with ganglion cell dysfunction. Some severely affected eyes showed P50 component involvement, but in no eye was the PERG extinguished. Significant interocular asymmetries in at least one electrophysiological measure were present in 6/13 patients. Colour contrast thresholds were significantly elevated for all three colour confusion axes, with tritan being most affected.

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.

The pattern electroretinogram in anterior visual pathway dysfunction and its relationship to the pattern visual evoked potential: a personal clinical review of 743 eyes

The pattern electroretinogram (PERG) has now been in routine clinical use for sufficiently long to allow a personal clinical review of its relationship to the cortically generated pattern visual evoked potential (PVEP). The PERG and PVEP findings are presented from 520 eyes with optic nerve demyelination (382 eyes), optic nerve compression (90 eyes) or heredofamilial optic atrophy (48 eyes), and these are compared with the findings obtained in 223 eyes with dysfunction anterior to the retinal ganglion cells. Dysfunction anterior to the retinal ganglion cells gives a reduction in the P50 component of the PERG, but this component is usually spared in optic nerve disease where selective loss of the N95 component is by far the most frequently occurring abnormality. A diagnostic strategy is presented.

Retest variability and diurnal effects in the pattern electroretinogram

Pattern electroretinograms were recorded to phase-reversing checkerboard stimuli with DTL electrodes under conditions close to those of the ISCEV pattern electroretinogram guidelines. Both transient (2 reversals/s) and steady-state (16 reversals/s) stimulation was used. The check sizes were 0.4 degree, 0.8 degree and 16 degrees; the mean luminance 45 cd/m2, the contrast 98%, and the field size 32 degrees x 27 degrees. In 42 eyes of 21 subjects, measurements were repeated at the same time of day after 1 week. For each eye, the intersession coefficient of variation was calculated as a measure of reproducibility. We found a coefficient of variation (+/- standard deviation) of 7% +/- 5% for the amplitude of the steady-state pattern electroretinogram, 9.5% +/- 7% for the transient pattern electroretinogram and 1.5% +/- 2% for the latency of the transient pattern electroretinogram. To assess the diurnal variability, during a 15-h period, three pattern electroretinograms were recorded in 10 subjects. No relationship was found between the P50 latency and the time of day. However, the mean amplitude showed a maximum in the morning (9:30 am) and a minimum in the afternoon (2:30 pm). This small effect (about 7%, p < 0.001) was more pronounced for N95 and steady-state amplitudes than for P50 amplitudes (p < 0.01). Diurnal contributions to the pattern electroretinogram ranged between 3% and 10%. We conclude that pattern electroretinogram amplitude reproduces within +/- 10% with a probability of 70%. The effect size of the diurnal variation is similar and might be relevant for longitudinal studies.