[A comprehensive detection and psocessing system of visual electrophysiological information based on interconnected computers]

This paper introduce a novel comprehensive system of visual electrophysiological information processing. The weak-light stimulator and surface-electrode are used to overcome the subject's unfitted sense led by Ganzifield stimulator and the cornea-touch electrode. Based on two computers which are interconnected, this system can work on pan-character picture stimulating mode. While working on line, it can dynamically display the process of test in real-time. It also offers a clear interface and integrated modules of information processing and analysis.

Precision LED-based stimulator for focal electroretinography

The authors discuss the technical problems commonly encountered in the design of devices used in the functional analysis of the central retina (macula) and its neuronal elements. They present a simple effective solution for introducing some of the most recent and interesting results of neurophysiological and psychophysical research into the eye clinic.

[Reproducibility of the pattern electroretinogram]

The pattern ERG (PERG) is used as an indicator of retinal ganglion cell function. Up to now, reports on the reproducibility of the PERG have been contradictory. We investigated the reproducibility under the conditions of the forthcoming ISCEV guidelines for the PERG. We simultaneously recorded the PERG and VEP in 42 eyes of 21 subjects to phase-reversing checkerboard stimuli with DTL electrodes. Both transient (2 rps) and steady-state (16 rps) stimulation was employed. 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. Measurements were repeated at the same time of day after 1 week. In addition, we compared two different electrode positions in 16 eyes: (1) across the cornea along the lower lid; and deep in the conjunctival sac. With position (1) the amplitudes were found to be higher by 20% than (2). We calculated the coefficient of variation (CV) of amplitude as a measure of reproducibility. CV was 7 +/- 1% for the steady-state PERG, 9 +/- 1% for the transient PERG, 12 +/- 2% for the steady-state VEP and 14 +/- 3% for the transient VEP. For the latency of the PERG, the intersession CV was found to be 1.5%. Amplitude reproducibility was somewhat higher under steady-state as compared to transient stimulation; we attribute this to the high noise rejection of the Fourier analysis. Altogether, the amplitude reproducibility of the PERG is somewhat higher than that of the VEP.

The inverse problem in electroretinography: a study based on skin potentials and a realistic geometry model

The problem of obtaining the retinal source distribution that generates the electroretinogram (ERG) from measured skin potentials is addressed. A realistic three-dimensional (3-D) volume conductor model of the head is constructed from magnetic resonance image (MRI) data sets. The skin potential distribution generated in this model by a dipole layer source at the retina is computed by using the boundary element method (BEM). The influence of the various compartments of the complete model on the results was investigated, and a simplified model was defined. An inverse procedure for estimating the source distribution at the retina from ERG's obtained from skin electrodes was developed. The procedure was tested on simulated potentials. A fair correspondence between the original and estimated source distribution was found. Furthermore, the ERG's measured at seven skin electrodes were used to estimate the source distribution at the retina. The ERG potential waveform at an additional skin electrode was computed from this source distribution and compared to the measured potential at this electrode. Again a fair correspondence was obtained. It is concluded that the methods may become a useful tool for clinical applications, i.e., for the assessment of localized defects in retinal function.

[Chronic open angle glaucoma: correlation of pattern electroretinography and visual field indices]

The pattern electroretinogram has already proven to be useful in detecting early stages of chronic open-angle glaucoma. We were interested in the degree of correlation between pattern ERG amplitudes and definite visual field defects. Fifteen glaucoma patients with a wide range of visual field defects were examined with pattern electroretinogram (stimulus with reversal rate of 8/s, checksizes of 0.9 degree and 6.9 degrees, covering a visual field of up to 9 degrees eccentricity). The patients' visual fields obtained with the Octopus 1-2-3 perimeter were analyzed with the perimetric analysis system PERIDATA using the indices of conformity for localized defects and the regional indices created from the mean deviation in certain parts of the 30 degrees field. In our results we were only able to find a significant correlation within the 5% level between the pattern ERG amplitudes and the sector index (large checksize, correlation coefficient r = -0.58, p = 0.03) and with the mean deviation in the region between 10 degrees and 20 degrees (small checksize, r = -0.538, p = 0.044). In summary, a marginal correlation between electrophysiological data and perimetric parameters was demonstrated. We try to explain the remarkable correlation between the amplitudes (small pattern) that were recorded from the central 9 degrees with the mean defects from the visual field peripheral of 10 degrees with the frequent combination of diffuse and localized field defects in glaucoma. Examination with the pattern ERG alone does not seem to be appropriate for grading the focal glaucomatous damage.

[Effect of cataracts on contrast pattern reversal stimuli exemplified by the pattern electroretinogram]

A cataract changes pattern-evoked contrast responses to a mostly unknown extent by a blurred retinal image. Pattern electroretinograms (P-ERG), evoked by a reversing checkerboard pattern, were measured (a) in 12 healthy volunteers with a cataract simulated by Bangerter foils; (b) pre- and postoperatively in 44 cataract eyes without retinal damage; and (c) in 13 healthy contralateral eyes. Slight media opacities (visual acuity 1.0 to 0.8) already diminished the amplitudes of the pattern ERG significantly, whereas the latencies did not react significantly. This can be explained by a decrease more in contrast than in luminance. Postoperatively, the amplitudes continued to increase during the first 10 weeks, when the visual acuity remained stable. The postoperative amplitudes did not reach the amplitudes of comparable healthy contralateral eyes. It is recommended that eyes be checked for cataracts before an interpretation is made.

[Changes in the electroretinogram of Campbell rats with the development of hereditary retinal degeneration]

We studied the dependence of amplitudes of a- and b-waves of electroretinogram on intensity of light stimulus in Campbell rats with inherited retinal degeneration. On 20-th-29-th day after birth the amplitude of these waves in Campbell rats is smaller than in Wistar rats. On 30-th-40-th day response significantly decreases, down to complete disappearance of reaction. Weak response appears only to stimulus with the maximal luminance. According to decrease of amplitude of the a- and b-waves of the ERG, Campbell rats are practically blind at 40th day of postnatal life. The analysis of the form of whole ERG curve using the Fourier transformation allowed us to establish, that in Campbell rats on 20-th day after birth the amplitude of the first and second harmonics grows with increasing of stimulus luminance. At 30-th day the amplitude of the second harmonic in Campbell rats is much smaller than in Wistar rats and does not vary with increasing of stimulus luminance.

[Skin electrodes for electroretinography in unsedated children]

Contact lens electrode ERG is not well tolerated by children. So far, skin electrode ERG has suffered from a weakly defined geometrical relationship to the sources of ERG potentials. Because of the cuplike electric ocular field distribution, skin electrodes were placed: (1) in the middle of the lower eyelid (in order to be positioned in close proximity to the anterior apex of the cornea, which belongs to the electropositive inner surface of the cup); (2) 20 mm laterally to the temporal canthus (in proximity to the cup's electronegative outer surface). (3) Grounding was achieved by attaching a third skin electrode in the forehead midline. Instead of complete dark adaptation, adaptive illumination of 0.1 cd.m-2 was used to avoid frightening the children. After 10 min of adaptation, the examination started. Feeling safe on mother's lap, the little patient looked into a frosted glass screen (about 75 degrees of visual angle, depicting Mickey Mouse) on which a series of strobe flashes was delivered along the lines of the ISCEV ERG Standard: (1) blue flashes: filter no. 625 (Röhm and Haas); repetition rate 0.1 Hz; stimulus strength of white flashes 1.5 cd.m-2 s; (2) red flashes: filter no. S502 (Röhm and Haas); repetition rate 1 Hz; stimulus strength of white flashes 21.75 cd.m-2.s; (3) weak white flashes: stimulus strength 1.5 cd.m-2.s; repetition rate 0.3 Hz; (4) strong white flashes: stimulus strength 11.25 cd.m-2.s; repetition rate 0.3 Hz; (5) white flicker flashes: stimulus strength 1.5 cd.m-2.s; frequency 10, 30, 60 Hz. Recording of single stimulus responses turned out to be feasible; however, to achieve the best results, between 8 and 32 ERG responses were averaged. To illustrate the benefits of skin electrode ERGs in practice, the results of some cases are presented and discussed with respect to clinical findings.

[Pattern electroretinography in routine clinical diagnosis of open angle glaucoma]

According to current opinion, the pattern electroretinogram (ERG) is generated in the retinal ganglion cells. Therefore, the amplitude is expected to be reduced in diseases of the optic nerve. This leads to the conclusion that the pattern ERG might be applied in detecting ganglion cell loss in the routine clinical diagnosis of chronic open-angle glaucoma. Pattern ERGs were recorded in 15 patients with defined chronic open-angle glaucoma and 21 control individuals using a DTL fiber electrode at two different check sizes. A Fourier analysis of the ERG results reduces the subjectivity when analysing the amplitudes on screen and implies the possibility of multicentric comparability. The reliability of coordinating a value of a future patient to the correct group was estimated to 82% for the Fourier data by the bivariate discriminant analysis, based on the amplitudes of both check sizes. In this way, the relatively high interindividual variability will be partly overcome. The ability of the ERG amplitudes to separate glaucoma patients from healthy persons was determined by the AUC value, using a combination of sensitivity and specificity extracted from the ROC curves. The AUC value has its maximum at 1.0. We found an AUC value of 0.8, which confirmed the information given by the pattern ERG amplitudes. Healthy individuals and glaucoma patients cannot be separated completely by the procedure but, combined with additional clinical parameters, further validation can be achieved.

Inter-hospital comparison of Ganzfeld ERG photostimulators

The periodic calibration and control of electroretinographic (ERG) stimulators is often neglected due to the difficulties in accurate measurements of the stimuli. Comparison of measurements carried out in different laboratories has been very difficult, as the accurate parameters of the stimuli used usually are not known. In some cases it is assumed that if the stimulator type is known, comparisons can be carried out. We have tested the Ganzfeld flash stimulators used in the departments of clinical neurophysiology of 3 major hospitals in Finland, namely Kuopio University Hospital, Turku Central University Hospital, and Tampere University Hospital, Measurements, performed with a new type of photometer, show that the intensities varied by 42% between the highest and lowest intensity stimulators at nominally identical settings. The measurements underline the findings that identical stimulators will not necessarily produce identical stimuli. These observations also indicate that the stability of the stimuli can be improved by the proper choice of stimulator output settings.

Contrast and luminance as parameters defining the output of the VERIS topographical ERG

The Visual Evoked Response Imaging System (VERIS I) topographical electroretinogram system (EDI Associates, San Francisco, CA) allows measurement of the response of large numbers of retinal areas simultaneously. This paper examines ERG responses derived with the VERIS system to changes in target contrast and to local reductions in luminance. There is a linear reduction of response with reductions of target contrast. Neutral density filters were placed over part of the display, to mimic the localised reductions in response which occur in glaucoma, age-related maculopathy or diabetic retinopathy. There is a definite reduction in response seen with a 0.4 ND filter, indicating that the system should have similar sensitivity in detection of retinal lesions to the commonly used visual field analysis systems.

Reproducibility of electroretinograms recorded with DTL electrodes

The purpose of this study was to examine whether the use of the DTL fiber electrode yields stable and reproducible electroretinographic recordings. To do so, luminance response function, derived from dark-adapted electroretinograms, was obtained from both eyes of 10 normal subjects at two recording sessions spaced by 7-14 days. The data thus generated was used to calculate Naka-Rushton Vmax and k parameters and values obtained at the two recording sessions were compared. Our results showed that there was no significant difference in the values of Vmax and k calculated from the data generated at the two recording sessions. The above clearly demonstrate that the use of the DTL fiber electrode does not jeopardize, in any way, the stability and reproducibility of ERG responses.

Guidelines for basic pattern electroretinography. Recommendations by the International Society for Clinical Electrophysiology of Vision

The pattern electroretinogram is a retinal response that can be evoked by viewing an alternating grating or checkerboard. It is receiving increasing clinical and research attention because it can provide information about inner retinal cells and the macula. However, clinicians may have trouble choosing between different techniques for recording the Pattern electroretinogram that have been described in the literature. The International Society for Clinical Electrophysiology of Vision has prepared guidelines for a basic pattern electroretinogram recording procedure to aid new users in obtaining reliable responses and to encourage more uniformity among existing users.

Effect of repeat use and coating defects of gold foil electrodes on electroretinogram recording

Qualitative defects and resistances in 94 used gold foil electrodes were examined. The electrodes were divided into four groups of varying resistances and gold coating defects. Ten were randomly selected from each group to measure standard photopic electroretinograms (ERGs) in a normal subject. Ten new electrodes were used as controls. There was no significant difference among the electrode groups for ERG peak implicit times or amplitudes, although a slightly greater amplitude variability was observed for the groups with more defects. Provided the resistance of the electrode is low ( < 5 omega), its reuse at least for ganzfeld ERGs appears warranted regardless of apparent coating defects.

Simultaneously recorded retinal and cerebral potentials to windmill stimulation

Visual evoked retinal and cerebral potentials were recorded to onset rotation of an isoluminant sectored disc. While the retinal potentials recorded to onset rotation closely resembled the electroretinogram to a checkerboard or stripe pattern of fixed element size, the visual evoked potential changed interindividually and intraindividually from a fast positive wave at high contrasts, velocities and number of windmill segments to a later negative component at low contrasts, velocities and windmill segments. With change in luminance, contrast, speed and extent of rotation field size and number of disc segments, the visual evoked potential was generally less affected than the electroretinogram.

Amplitude scaling relationships of Burian-Allen, gold foil and Dawson, Trick and Litzkow electrodes

The bipolar Burian-Allen electrode represents the International Society for Clinical Electrophysiology of Vision standard for recording the electroretinogram. With prolonged recording there is a high risk of corneal abrasion from the electrode, while alternatives such as gold foil electrodes or fibers represent less risk. The standards require that alternative electrodes be demonstrated to give equivalent waveform and amplitudes. Electroretinograms were recorded with the bipolar Burian-Allen electrode and four alternative electrode configurations: a unipolar Burian-Allen electrode, a bipolar and monopolar gold foil electrode and a Dawson, Trick and Litzkow fiber electrode with all other recording conditions identical. The results represent a guide for comparisons of electroretinograms between studies using these electrodes. Recordings were made from two subjects for all five electrode configurations and six additional subjects with unipolar gold foil and bipolar gold foil electrodes alone. Flash stimuli over a range of intensities from full intensity to -1.5 log units were used. Recordings were repeated in the one session and on a subsequent session to provide test-retest reliabilities. Significant (p < 0.0001) differences in b-wave amplitude resulting from electrode type and intensity were demonstrated. The unipolar Burian-Allen and unipolar gold foil electrodes produced the greatest amplitude responses. The alternatives to the bipolar Burian-Allen electrode were equally or more reliable. The Dawson, Trick and Litzkow electrode produced lower-amplitude response than the bipolar Burian-Allen electrode but was the only one with significantly greater between-session reliability.

Blue light-emitting diode built-in contact lens electrode can record human S-cone electroretinogram

PURPOSE

To develop a contact lens electrode with a built-in blue light-emitting diode (LED) to record the electroretinogram from short-wave sensitive-cone (S-cone) electroretinogram (ERG) in humans.

METHODS

The ERG was recorded using the blue LED (450 nm) built-in electrode under a yellow background illumination from a slide projector in five normal subjects, a patient with blue cone monochromatism, and a patient with fundus albipunctatus. For comparison, the ERG was also recorded using a yellow LED (566 nm) built-in electrode under the same background illumination in the normal subjects.

RESULTS

The amplitude and the peak time of the b-wave recorded with 3-Hz blue stimuli were 5.1 to 12.4 microV and 63 to 68 msec, respectively in normal subjects, 7.3 microV and 65 msec in the patient with blue cone monochromatism, and 11.4 microV and 65 msec in the patient with fundus albipunctatus. Normal subjects responded to neither 30-Hz blue stimuli nor 3-Hz yellow stimuli.

CONCLUSIONS

Results indicate that the b-wave recorded with 3-Hz blue stimuli is elicited from the S-cone system. This simple technique is useful for testing the human blue cone system.

An electrode to record the mouse cornea electroretinogram

The mouse has become a popular model for the study of retinal degeneration, but an electrode suitable for recording electroretinograms from the mouse cornea is not available commercially. I developed a simple electrode suitable for the relatively small mouse eye by attaching a thin stainless-steel wire through the barrel of a 1-cc syringe. The end of the wire is formed into a coil by wrapping it around a 0.5- or 1.0-mm pin. The syringe barrel serves as a convenient way to hold the electrode in a goose-neck holder. This electrode has been used successfully to obtain electroretinograms from hundreds of mice as young as 14 days.

[A PC program for evaluating electrophysiologic signals of mammalian eyes]

BACKGROUND

Electrophysiological measurements in the mammalian eye in vivo or in vitro, i.e. in the arterially perfused cat eye, require storage and analysis of a large amount of data: light-evoked signals, including the electroretinogram (ERG) and the optic nerve response (ONR) are stimulus-related and have to be measured in a triggered mode, whereas the DC-standing potential and flow rate of perfusion medium should be measured continuously.

METHOD AND RESULT

In order to facilitate the analysis of these various signals, we developed a computer program, that allows an on-line data analysis and a trend indication for pharmacologically induced changes in signal size as well as efficient storage. The flexible system is based on a "labview" program, the application and efficiency of which are discussed.

Design of a new disposable ERG electrode

A new electrode for electroretinography (ERG) has been produced. The new device made of gold filament was applied as corneal and noncorneal electrod. Flash ERG and pattern ERG were recorded in normal subjects using this new electrode and compared with those made by available electrodes. There were so significant differences in amplitude and latency between the new electrode placed on the cornea and the JET-type electrode. For pattern ERG there were no significant differences between the new electrode placed in the lower fornix and a gold-foil-type electrode. As this new electrode is less expensive and more comfortable than the available electrodes, it is clinically useful.

[The electroretinogram of the dark-adapted intact carp Carpio cyprinus L. to color substitution]

Electroretinogram b-wave was studied in intact carp using instantaneous substitution of monochromatic stimulus for another one in the range of 404-681 nm. It was shown that the amplitude of the b-wave as a function of the wavelength was good approximated by the spectrum of a scotopic pigment (porphiropsin) with the absorbtion maximum near 530 nm. The amplitude of the b-wave recorded during alternation of different monochromatic stimuli was determined only by their intensity differences and the level of previous light adaptation.

[15 years automated perimetry--where does the path lead?]

15 years ago the first fully automated perimeter became available, the Octopus 201, developed by Fankhauser in Bern. Some of the objections which were raised in those days against automated perimeters have turned out true, many, however, not. From todays perspective automated perimetry has brought tremendous advantages for clinical routine diagnosis. The essential power of automated perimetry is its ability to obtain quantitative data which can be processed statistically. The examination of the central visual field may be performed in a much more sophisticated way than by manual kinetic testing. Automated perimetry, however, also has its draw-backs, which are mostly due to mistakes or errors by the examiner, not so much to the method itself. For routine light-sense perimetry the upcoming years will give us faster and optimized testing strategies. Procedures for automated interpretation of visual field data will be developed. The interest in more complex perimetric test criteria goes on one hand into the direction of independence of disturbancies of the optical media (e.g. temporal criteria), on the other hand into the differentiation of various cell populations in the visual system (Blue/Yellow-Perimetry; Motion-Defined-Form etc.). For objective perimetry a powerful system for pattern-ERG and pattern-VECP with a spatial resolution comparable to standard perimetric tests is available. Also in these fields of perimetry the coming years will bring interesting and revolutionary new developments which will open new diagnostic dimensions.

[A procedure for recording electroretinogram (ERG) with a contact lens-type electrode, and effect of sodium iodate on ERG in rats]

A procedure for recording the electroretinogram (ERG) in rats with a contact lens-type electrode was developed in order to examine visual toxicity overtime. Rats received a single intravenous injection of sodium iodate (SI), a retinotoxic compound, via the tail vein at a dose of 12.5, 20, 25 or 50 mg/kg, and the ERG was recorded for 10 days after dosing. Histopathologic examination of the retinas was then conducted. 1. The rats were anesthetized with ketamine hydrochloride (50 mg/kg, i.m.) after 90 to 120 min of dark-adaptation. Thirty-two responses to repetitive 1.2 joule light stimuli at 0.5 Hz interstimulus intervals were averaged by a microcomputer. Under these conditions, stable ERG a-wave, b-wave and oscillatory potentials could be recorded for 10 days. 2. At 12.5 mg/kg of SI, no treatment-related abnormalities were observed on the ERG. Doses of 20 mg/kg or more of SI caused depression of the amplitudes of the ERG a-wave and oscillatory potentials 2 hrs or 1 day after dosing. Following these changes, the amplitude of the ERG b-wave decreased 1 or 2 days after dosing. 3. Upon histopathologic examination of the retina, folding of the outer nuclear layer, disarrangement of the rods and cones and swelling and decrease of the pigment epithelial cells were observed at 20 mg/kg or more. The severity of the retinal lesions correlated well with the changes in the ERG. 4. Using this recording technique, it was confirmed that a stable ERG could be recorded repeatedly in rats, and the effects of SI on the ERG could be detected. Furthermore, histopathologic examination revealed that the severity of the retinal lesions correlated well with the changes in the ERG. These results indicate that the ERG recording technique employed in this study is useful for evaluating retinal toxicity in rats.