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This study suggests a model by which we try to explain why coating agents habitually applied in electroretinography can change the amplitude of electroretinographic responses. The model is based on the results of experiments described in this paper. The accuracy of measurement in clinical and experimental electroretinography can be enhanced by applying this model.
Rapid developments in human electroretinography during recent decades have greatly increased its value for investigating psychophysical problems. This review of the current status of electroretinography considers the response waveform, recording techniques, and data analysis. Several examples of electroretinal data that have psychophysical significance are presented.
Conventional electroretinography requires the application of a ring or contact electrode to the anaesthetized cornea. A simplified method for routine clinical electroretinography is described. Skin electrodes are used, signals are appropriately filtered, amplified, passed to a signal averager and displayed on an oscilloscope. Sixteen sweeps are employed and a wave form similar in appearance and frequency content to that obtained by the corneal electrode method, is obtained. Values for the light and dark adapted eye in normal subjects (pupils undilated), are provided and the findings in the stages of retinitis pigmentosa and in other disease states, are noted.
Twenty-four patients with proliferative or preproliferative diabetic retinopathy underwent extensive argon laser photocoagulation in one eye. Detailed central and peripheral visual-field examinations and electroretinography were performed before treatment, and at intervals after treatment. Visual field changes were as follows: (1) eight patients had only mild to moderate constriction of all isopters, (2) 11 had discrete scotomata in addition, (3) two had prominent nerve-fiber-bundle defects, (4) three had severe constriction of all isopters, save (in two) that to the largest peripheral test object. Electroretinographic b-wave amplitudes were reduced an average of 40% to white test flashes. Blue test flashes showed an even larger reduction of the rod response. This suggests the receptors in approximately 40% of the retinal area are destroyed by such extensive photocoagulation, covering predominantly that part of the retina that has the highest concentration of rods.
The design of a ganzfeld stimulator for electroretinography affects both clinical results and ease of operation. Several advantageous design differences from a recently described ganzfeld stimulator are (1) close proximity of the flash electrode to the surface of the sphere to increase the intensity and uniformity of the stimulus; (2) provision for interposing color filters in the background light; (3) use of a diffusing filter in the background light; and (4) placement of the stimulus flash anteriorly to avoid uneven illumination of the retina. Details of construction are proveded for two models and the specific advantages of each design are noted.
The developement of chalcosis bulbi in rabbits' eyes is investigated by ophthalmoscopy, electroretinography, and diagnostic x-ray spectrometry (DXS), a new method for in vivo analysis and quantitation of metals. The DXS is shown to provide an effective method for the early detection of intraocular foreign bodies (IOFB) dissolution. The ophthalmoscopic changes observed in chalcosis are discussed in relation to dissolution of IOFB and electroretinographic findings.
A new noncorneal electrode for clinical electroretinography was developed. It consists of a thin wire forming a loop modeled to fit into the lower conjunctival sac. Electrical contact is made with the scleral conjunctiva through an exposed portion of otherwise insulated wire. The recorded pattern electroretinograms are in the same amplitude range as if recorded by the gold foil electrode, while the flash electroretinograms with the new electrode are of about two-thirds the amplitude of corneal electrodes. The new electrode is more durable and hence less expensive than gold foil electrodes and can likewise be used without topical anesthetic. Cleaning is easy and effective. The electrode rarely causes discomfort and produces stable responses for at least 2 hours. The electrode aims to match stability of skin electrodes with sensitivity of fragile foil and fiber electrodes.
Clinical evaluation of the function of the human retina by subjective, psychophysical tests can be complemented by objective, electrophysiological methods such as electroretinography. The electroretinogram (ERG) is a transient action potential generated by the vertebrate retina in response to light. Using standardized stimulation, after assessing the normal range of the ERG the investigator can establish early diagnosis, improve prognostic statements and document the course of retinal diseases. A method to selectively stimulate the rod- and cone-system, developed by Gouras and co-workers, has proved to allow further differentiation of heredodegenerative diseases of the retina. The ERG monitors objectively the function of the retina in infants uncapable of cooperating in psychophysical tests and in patients suffering from opacities of the optic media. ERG results should be evaluated synoptically with psychophysical data, ophthalmoscopy, fluoresceinangiography and possibly with EOG and VER recordings. Under experimental conditions the ERG serves to monitor the sensitivity of the retina in vivo as well as in vitro in physiological, pharmacological and toxicological studies.
In electroretinography, coating agents are usually applied to improve the contact between the contact-lens electrode and the eye. These agents influence electroretinographic responses. In this experimental study we show that the characteristic properties of the electrode circuit are not influenced by the coating agent. Thus we conclude that these coating agents influence the eye itself. The mechanism of this interaction may be physical, or may be an unknown pharmacologic drug side effect.
Retinal mechanisms have been hypothesized in the pathophysiology of seasonal affective disorder (SAD). Electroretinography (ERG) is a noninvasive electrophysiologic test that provides an objective measure of photoreceptor and retinal function. We conducted dark-adapted ERG examinations with a bright white light stimulus in a group of depressed, drug-free patients with seasonal affective disorder (6 men, 18 women) diagnosed by DSM-III-R criteria, and a group of sex- and age-matched control subjects (6 men, 16 women) during the winter. A significant difference was found between SAD patients and controls, but female SAD patients had lower ERG b-wave amplitudes than female controls, while male SAD patients had higher amplitudes than the matched controls. The ERG b-wave implicit times (times from onset of stimulus to peak of b-wave) were significantly longer in the left eyes of the male control subjects. These data may indicate subtle retinal changes in patients with SAD, but the results must be considered preliminary because of the small number of subjects studied and the large intersubject variability in the ERG procedure.
An electrode for electroretinography was developed that fits over the patient's lower lid. The electrode incorporates a platinum strip embedded in a piece of shaped plexiglass. The electrode was standardized for clinical use by comparing ERG recordings from this platinum lid electrode with those recorded from a Burian-Allen electrode. The a- and b-wave implicit times and amplitudes were measured in four subjects, using both electrodes under varying luminance conditions, to provide a measure of the validity of the platinum lid electrode. The same experimental procedure was repeated five times on two individuals to provide a measure of the reliability of both electrodes. Results indicate amplitudes approximately 65% of those recorded with a Burian-Allen electrode but which are otherwise in good agreement.
In view of the finding that dopamine is the principle neurotransmitter in the retina, an attempt was made to demonstrate dopaminergic receptor blockade by means of electroretinography. In an open experimental setting, the effect of 50 mg thioridazine was compared with that of placebo in 2 groups of 10 normal volunteers. In the placebo group, the post-drug scotopic electroretinogram (ERG) was not significantly different from the pre-drug ERG, while in the thioridazine group, the post-drug scotopic ERG showed prolongation of 'a' wave latency time, prolongation of 'b' wave evolution time, and diminution of 'b' wave amplitude.
Clinical electroretinography is an uncomfortable, disquieting experience for a patient because of the contact lens electrodes used. Such electrodes are either expensive to buy or difficult to make. An aluminized Mylar electrode performs satisfactorily, elicits minimal patient apprehension or discomfort without topical anesthesia, is simple to make, and is disposable.
A new procedure is described for cone electroretinography using a cross-correlation method of signal processing to give the response to flash stimuli which occur at randomly timed intervals. The output waveform is different than the usual repetitive flicker response, and can be presented on any desired time base. An unfamiliar aspect of this process is that most of the random time intervals between consecutive stimuli are shorter in duration than the output waveform. For the parameters described, the output waveform gives the response to approximately 1,640 stimuli in 65.5 sec., with a signal-to-noise ratio which is higher than that obtained when conventional averaging techniques are used over similar time periods. This allows more precise and statistically significant estimates to be made of the time and amplitude parameters of the cone response. Normal values are given for implicit (delay) time and amplitude, and examples are provided for comparison of the random flash response and conventional average electroretinograms (ERG's) in normal subjects and patients with retinal degeneration.
In this paper, further investigation by fluorescein angiography and electroretinography (ERG) was undertaken to substantiate the possible toxic maculopathy due to quinine usage. Again, positive Amsler chart tests were found in 3 of 14 (21%) of the drug addicts with blurred vision, a common complaint among these patients. The results of 5 fluorescein angiography examinations demonstrated no leakage of dye, especially in the macula. Twenty-four ERG examinations revealed no statistical differences between the test group patients and the control subjects. It was concluded that there is a definite need to carefully examine the eyes of any person who has used quinine for a long time since positive Amsler chart tests were found in 37% of the drug addicts.
The authors report 20 cases of a syndrome named nephronophtisis and probably the same as the syndrome of medullar cystic disease. In all cases systematic electroretinography is performed. Nine cases show important deterioration of the outline. These cases can be included in the syndrome of Senior-Loken. The pathogenesis and familial character of this disease are discussed. The disturbances that appeared between the ocular and renal lesions suggest that there are probably two genes rather than a single pleiotropic gene.
Corneal electrodes useful for clinical electroretinography require topical anesthesia, interfere with vision, can abrade, and are not well accepted by most children and many adults. A low mass conductive thread, corneal (DTL) electrode is described and comparatively tested against the Burian-Allen electrode. The DTL electrode was found to have few of the limitations of the hard contact lens electrode. Furthermore, the DTL electrode signal quality was comparable to that of the Burian-Allen electrode and provided less between-patient variability.
Electroretinography revealed unsuspected night blindness in a patient who had suffered unilateral trauma. This case illustrates the importance of testing both eyes, even when one appears normal.