Pattern electroretinogram: use of noncorneal skin electrodes

Bayley Mental Scale of Infant Development and Visually Impaired Children

Twenty infants and toddlers were determined to be visually impaired based on an ophthalmological examination and electrophysiological testing (Visual Evoked Response). To assess changes in visual-motor function with age, the 20 visually impaired infants and toddlers were followed, longitudinally, with the Bayley Mental Scale of Infant Development (BMSID). Based on the longitudinal BMSID data the study revealed the infants and toddlers obtained a range of scores. The results of the BMSID are discussed within the context of its role as a comprehensive assessment tool that charts changes in the visual-motor function of visually impaired children.

Clinical Trial to Evaluate Safety and Efficacy of Transdermal Electrical Stimulation on Visual Functions of Patients with Retinitis Pigmentosa

To evaluate the safety and efficacy of transdermal electrical stimulation (TdES) with skin electrodes on improving the visual functions of patients with retinitis pigmentosa (RP), twenty eyes of 10 patients with RP underwent TdES (10-ms biphasic pulses, 20 Hz, 30 min) 6 times at 2 week intervals. All patients were stimulated bilaterally with 1.0 mA pulses. The primary endpoint was safety, and the secondary endpoints were the changes in the best-corrected visual acuity (BCVA), visual fields determined by the Humphrey field analyzer (HFA) 10-2 and Goldmann perimetry, and answers to the Visual Function Questionnaire-25. All of the 10 enrolled patients completed the study according to the protocol. No adverse events related to the treatments were reported during the follow-up examinations. The mean BCVA and Early Treatment Diabetic Retinopathy Study visual acuity were significantly improved after the TdES (P = 0.0078 and P = 0.001, respectively). The mean deviation of the HFA 10-2 was also significantly improved (P = 0.0076). We conclude that TdES with skin electrode is a safe therapeutic option and should be considered as a treatment option for patients with RP.

Evaluation of light- and dark-adapted ERGs using a mydriasis-free, portable system: clinical classifications and normative data

PURPOSE

The full-field electroretinogram (ff-ERG) is a widely used clinical tool to evaluate generalized retinal function by recording electrical potentials generated by the cells in the retina in response to flash stimuli and requires mydriasis. The purpose of this study was to determine the intra-visit reliability and diagnostic capability of a handheld, mydriasis-free ERG, RETeval (LKC Technologies, Gaithersburg, MD, USA), in comparison with the standard clinical ff-ERG by measuring responses recommended by the International Society for Clinical Electrophysiology of Vision (ISCEV).

METHODS

This prospective, cross-sectional study included 35 patients recruited at the Hospital for Sick Children (median age = 17, range 11 months-69 years) who had undergone a clinical ff-ERG according to ISCEV standards. For RETeval (n = 35), pupils were undilated in most (n = 29) and sensor strip electrodes were placed under the inferior orbital rim. Stimulus settings on RETeval were equivalent to those used in the clinical ERG. Fifty-seven control participants (median age = 22, range 8-65 years) underwent undilated RETeval ERG to establish standard values for comparison. Patient waveform components with amplitudes < 5th percentile, or implicit times > 95th percentile of normal relative to control data were classified as abnormal for the RETeval system.

RESULTS

The RETeval system demonstrated a high degree of within-visit reliability for amplitudes (ICC = 0.82) and moderate reliability for implicit times (ICC = 0.53). Cohen's Kappa analysis revealed a substantial level of agreement between the diagnostic capability of RETeval in comparison with clinical ff-ERG (k = 0.82), with a sensitivity and specificity of 1.00 and 0.82, respectively. Pearson's correlations for clinical ERG versus RETeval demonstrated a positive correlation for amplitudes across the rod (r = 0.65) and cone (r = 0.74) ERG waveforms. Bland-Altman plots showed no bias between the mean differences across all amplitude and implicit time parameters of the two systems.

CONCLUSIONS

The present study demonstrated that RETeval is a reliable tool with reasonable accuracy in comparison with the clinical ERG. The portable nature of RETeval system enables its incorporation at resource-limited centers where the ff-ERG is not readily available. The avoidance of sedation and pupillary dilation are added advantages of RETeval ERG.

Reproducibility of pattern electroretinogram in glaucoma patients with a range of severity of disease with the new glaucoma paradigm

PURPOSE

To determine the reproducibility of the pattern electroretinogram with the new Pattern Electroretinogram for Glaucoma (PERGLA) recording paradigm in glaucoma patients with a range of severity.

DESIGN

Experimental study.

PARTICIPANTS

Fifty-three glaucoma patients were recruited for the study (mean age +/- standard deviation [SD], 69+/-11 years). Their mean deviation (MD) global indices on static automatic perimetry ranged from 2.16 to -31.36 decibels (mean MD, -9.05).

INTERVENTION

All patients had pattern electroretinogram recordings done 5 times by the same operator, on 5 different days with the standardized PERGLA paradigm.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microvolts), phase (pi radians), response variability (coefficient of variation [CV] = SD/mean x 100) of amplitude and phase of 2 partial averages that build up the pattern electroretinogram waveform, interocular asymmetry in amplitude and phase (in terms of the CV generated by the pattern electroretinogram software), signal-to-noise (S/N) ratio, SDs, CV, and intraclass correlation coefficient (ICC). All analyses were done on one eye of each subject, except when interocular asymmetry was studied.

RESULTS

The CVs of intrasession variabilities in amplitude and phase were 12.08% and 2.20%, respectively, and those of intersession variabilities were 20.82% and 4.17%. The pattern electroretinogram produced intersession ICCs in amplitude and phase of 0.791 and 0.765, respectively. These ICCs were significantly higher than the ICCs for pattern electroretinogram interocular asymmetry in amplitude and phase (0.659 [P<0.05] and 0.571 [P<0.05], respectively). On average, the pattern electroretinogram S/N ratio in glaucomatous patients was about 5:1.

CONCLUSIONS

The reproducibility of PERGLA in glaucomatous patients is sufficiently good for it to be considered a useful complementary clinical tool. Being more reproducible, direct measures of amplitude and phase should be more useful in monitoring progression than interocular asymmetry comparisons.

Reflections on visual evoked cortical potentials and selective attention: methodological and historical

Details of research in which Russ Harter participated in his formative years are reviewed. Harter's participation in the early work on Visual Selective Attention (Eason, Harter & White, 1969) probably contributed most importantly to his career. While reviewing Russ's early experience with basic vision research and pioneer visual evoked potentials (VEPs), there is reference to extensive information regarding stimulus effects on VEPs (exogenous components of the ERP). There can be complex early and late waveforms and waveform changes with changes in certain stimulus conditions. There are critical peripheral vision effects at various loci over the visual field on VEP and reaction time. Special emphasis is given to effects of individual differences in training and skill of experienced subjects, as well differences in ability. These observations may suggest methods for optimizing sensitivity of ERPs and possibly some clues toward further understanding of ERPs.

Dark-adapted luminance-response functions with skin and corneal electrodes

Normative dark-adapted electroretinograms were recorded simultaneously with a skin electrode and corneal electrode for varying stimulus intensities. The electroretinogram b-wave amplitudes for each electrode were fitted by the Naka-Rushton equation, and the parameters Vmax, K and n were evaluated. A comparison of parameters between the two electrodes showed a significant difference for Vmax and K but not for n. Vmax was approximately eight times smaller and K was 0.3 log unit smaller for the skin electrode than for the corneal electrode. B-wave amplitude and implicit time were also compared between the two electrodes. The b-wave amplitude ratio of the corneal electrode to that of the skin electrode increased with luminance and ranged from 1.83 to 7.68. Overall, b-wave implicit time for the skin electrode was approximately 10 ms shorter than that of the corneal electrode.

Pattern ERG: effects of reference electrode site, stimulus mode and check size

We studied monocular pattern ERG (PERG) in 10 normal subjects and a patient with optic neuritis. No clinically significant PERG could be recorded from the occluded eye with any reference (ipsilateral ear or temple, or midfrontal), indicating that cross-contamination is not present with binocular testing. Ipsilateral temple reference minimized VEP (P100/N100) contribution to the PERG N95 which occurred with ipsilateral ear or midfrontal reference. The conclusions were confirmed by results from the patient, who had marked monocular delay of a normal amplitude P100. Twenty-four subjects were tested with monocular and binocular stimulation using an ipsilateral temple reference. There were differences in PERG latencies and amplitudes although the interside amplitude ratio showed smaller differences with binocular stimulation. Increasing check size (17, 35 and 70 min) decreased P50 and N95 latencies and increased P50 amplitude.

Screening of school-aged hearing impaired children

Three hundred sixty hearing-impaired students were screened for visual problems, including Usher's syndrome, with a complete ophthalmologic exam and electroretinography (ERG). Over 25% were found to have a significant refractive error, and approximately 32% had one or more pathologic findings. Overall, 43% either had a significant refractive error or pathologic finding. The incidence of Usher's syndrome was estimated to be between 1.1% and 1.9% in the hearing impaired student population. The results emphasize the need for a complete ophthalmologic examination, and possible ERG testing, in the hearing impaired student population.

Pattern electroretinogram: effects of reference electrode position

The pattern electroretinogram has assumed greater clinical and experimental significance because of its inner retinal origins. However, clinical tests may be confounded by an artifact. We tested subjects varying reference electrode position and eye stimulated while employing the Dawson-Trick-Litzkow (DTL) fiber electrode as the active electrode. The presence of a statistically significant artifactual response could not be confirmed. However, the variability of responses elicited with the outer canthus was less and the signal-to-noise ratio greater than with other reference positions.

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.